Review Article B Lymphocytes: Development, Tolerance, and...

Hindawi Publishing CorporationAutoimmune DiseasesVolume 2013 Article ID 827254 17 pageshttpdxdoiorg1011552013827254

Review ArticleB Lymphocytes Development Tolerance and Their Role inAutoimmunitymdashFocus on Systemic Lupus Erythematosus

Gabriel J Toboacuten Jorge H Izquierdo and Carlos A Cantildeas

Department of Internal Medicine Division of Rheumatology Fundacion Valle del Lili ICESI University School of MedicineCra 98 No 18-49 Cali Colombia

Correspondence should be addressed to Gabriel J Tobon gtobon1yahoocom

Received 30 June 2013 Accepted 6 August 2013

Academic Editor Juan-Manuel Anaya

Copyright copy 2013 Gabriel J Tobon et alThis is an open access article distributed under theCreativeCommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

B lymphocytes are the effectors of humoral immunity providing defense against pathogens through different functions includingantibody production B cells constitute approximately 15 of peripheral blood leukocytes and arise from hemopoietic stem cellsin the bone marrow It is here that their antigen receptors (surface immunoglobulin) are assembled In the context of autoimmunediseases defined by B andor T cell autoreactive that upon activation lead to chronic tissue inflammation and often irreversiblestructural and functional damage B lymphocytes play an essential role by not only producing autoantibodies but also functioningas antigen-presenting cells (APC) and as a source of cytokines In this paper we describe B lymphocyte functions in autoimmunityand autoimmune diseases with a special focus on their abnormalities in systemic lupus erythematosus

1 Introduction

Systemic lupus erythematosus (SLE) is the prototype of thesystemic autoimmune diseases characterized by multiorganinvolvement This systemic compromise is mediated by aglobal loss of self-tolerance The loss of tolerance is aconsequence of genetic factors in the context of specificenvironmental triggers with the subsequent developmentof an altered immune response Both innate and acquiredimmunemechanisms are implicated in the disease pathogen-esis Recently special attention has been focused on the Bcell abnormalities In this paper we will describe the B celldevelopment tolerancemechanism and their implications inautoimmune diseases with emphasis on SLE

2 B Cell Development and the B CellReceptor Formation

Different populations of B cells result in preimmune poolswhere each cell in these quiescent populations expressesa B cell antigen receptor (BCR) with a unique specificityWhen the BCRs come in contact with their specific antigenseveral intracellular signals are generated leading to acti-vation differentiation and formation of plasma cells and

memoryB cellsThis last subset of B cellsmaintains protectiveantibody levels and mediates the response to subsequentantigen challenges As the mechanisms leading to maturingand antibody production are complex the alterations of someof these populations or critical steps have been associatedwith immunodeficiency and autoimmune diseases Table 1summarizes the most important features of each of thesubpopulations (lineages) of B lymphocytes [1]

21 B Cell Development This process begins from stem cellspresent in the bone marrow (BM) which depending on thedifferent stimuli received will generate B lymphocytes Theyare derived from the early lymphoid progenitor which passesto the common lymphoid progenitor This produces firstof all the natural killer (NK) cells and dendritic cells andsecondly the common lymphoid-2 progenitor (LCA-2) thatis responsible for the B cell lineage which is considered thefirst stage of immature B lymphocytes Development of the Bcell lineage depends on BM stromal cells that producemainlyinterleukin (IL)-7 but also the Fms-like tyrosine kinase 3(Flt3-L) and on the action of several transcription factors suchas PU1 IKAROS (IKAROS family zinc finger 1) E2A EBF(early B cell factor 1) PAX5 (paired box gene 5) and IRF8(interferon regulatory factor 8) [2ndash5] In the BM B cells pass

2 Autoimmune Diseases

Table 1 Characteristics of primary B cell subsets and their progenitors

Differentiation Subset Surface phenotypeProgenitor subsets (bone marrow) Pro-B B220loCD43+

AA41+Pre-B B220loCD43minus AA41+preBcR+Immature (23minus) B220lo sIgM+ sIgDminus CD23minusImmature (23+) CD19+ B220+ sIgM+ sIgDminus CD23+

Transitional subsets (spleen) T1 IgMhiCD23minus B220intAA41+T2 IgMhiCD23+ B220+AA41+T3 IgMloCD23+ B220+AA41+

Mature primary subsets Follicular zone IgMloCD23+ B220hiAA41minusMarginal zone CD19+IgMhiIgDlo CD23+ CD21+B1 CD43+ CD23minus CD5+

T-independent responses Early antibody-forming cellsshort-lived plasma cells B220loCD19+slg+iclghiT-dependent responses Early antibody-forming cellsshort-lived plasma cells B220loCD19+slg+iclghi

Germinal center B220+CD19+GL7+Long-lived plasma cells B220loslgminusiclg+Memory B220+slg+IgDminus

Natural antibodies Peritoneal B1a and B1b CD43+ CD23minus CD5+

through several distinct developmental stages During thisthey acquire their antigen specificity follow a program of dif-ferential surface antigen expression and sequential heavy andlight chain gene rearrangement forming the BCR (initiallyIgM) that determines the cell maturation stage Reachingthe immature stage B cells exit the BM and complete theirdevelopment to the mature or naıve stage which is signaledby the appearance of IgD in addition to IgM on the cellsurface This development sequence occurs in the absenceof any contact with exogenous antigen a stage known asantigen-independent B cell development [2ndash5]

22 B Cell Receptor Development Immunoglobulin mol-ecules are composed of 2 identical 50 kd heavy chainsand 2 identical 25 kd light chains [6] The genes encodingimmunoglobulins are assembled from segments in a mannerthat is entirely analogous to the process of T cell receptorgenes The light and heavy chain loci are each composed ofa series of V (variable) gene elements followed by severalD (diversity) segments (for the heavy chain gene only)some J (joining) segments and C (constant region) exonsHeavy chains (H) are assembled from 4 segments (VHD JH and CH) Light chains (L) are assembled from 3segments (VL JL andCL) (Figure 1)The genes for 9 differentheavy chain types (IgM IgD IgG1ndash4 IgA1-2 and IgE) arelocated on chromosome 14 and those for 2 light chaintypes (120581 or 120582) are on chromosome 2 and 22 respectivelyThe variable portions (V) of the H and L chains are injuxtaposition and this creates the antigen-binding portionof the immunoglobulin molecule These V regions contain3 highly variable subregions or hypervariable sequenceswhich produce the antigen-binding domain of the moleculeThe amino-terminal portions of the chains vary in aminoacid sequence from one antibody molecule to another Thecarboxyl terminal portions are constant in each subclass ofantibody The H chain constant regions form the Fc domain

of the molecule and are responsible for most of the effectorfunctions of the immunoglobulin molecule

The development process of different subsets of B cells hasbeen extensively reviewed elsewhere [4ndash7] and summarizedin Figure 1 Once a functional IgM and IgD are synthesizedthe pre-B cell evolves into an immature B cell The fullymature BCR includes additional transmembrane proteinsdesignated as Ig120572 and Ig120573 that activate intracellular signalsafter receptor binding to antigen [8 9] At that point thematureB cell passes to peripheral lymphoid tissues (Figure 2)

23 B Cell Classification according to Their Ontogenic StateAs soon as B cells have productively rearranged theirimmunoglobulin genes pro-B cells proceed to the pre-B cellstage On their arrival in the spleen immature B cells give riseto type-1 (BT1) type-2 (BT2) and possibly type-3 transitionalB cells [11] As transitional B cells they are pushed intomigrating from the BM to secondary lymphoid organs (SLO)Although T1 cells undergo apoptosis in response to BCRengagement they require signaling via the B cell activatingfactor belonging to the tumor necrosis factor (TNF) familyreceptor (BAFF-R TNFRSF13) to mature to the T2 stage[12] T2 cells are only present in the spleen and reside in thefollicles whereas T1 cells are found in the red pulp and outerperiarterial lymphatic sheath (PALS) [13]

There they continue maturing and are furtherselected by antigens As BT1 they present asCD20+CD5+CD10+minusCD21+minusCD23+minusIgM+IgD+minus andCD38+ but once they have evolved to type 2 (BT2) theybecome CD20+CD5+minusCD21++CD23+minusIgM++IgD++ andCD38+minus T2 B cells differentiate into either circulatinglymphocytes that get organized as germinal centers (GCs)or noncirculating lymphocytes that populate the marginalzone (MZ) Progression of T2 B cells towards MZ or GCsmay be determined by the quality of BCR-evoked signalsand the subsequent expression of the Notch proteins [14]

Autoimmune Diseases 3

V V D D J J C C

Heavy chain gene

Heavy chain

V V J J C

Light chain gene

Light chain

COOH

COOHTMCIT

Immunoglobulinmolecule

NH2

NH2 VL CLJL

VH DH JH CH1 CH2 CH3 CH4

Figure 1 Schematic representation of the components of the H andL chains of immunoglobulins The light and heavy chain loci areeach made up of a series of V (variable) gene elements followedby several D (diversity) segments (for the heavy chain gene only)some J (joining) segments and C (constant region) exons Heavychains (H) are assembled from 4 segments (VH D JH and CH)light chains (L) are assembled from 3 segments (VL JL and CL)The development of the BCR begins when the recombinase enzymecomplex catalyzes the fusion of one DH region gene to a JH regiongene with the deletion of the intermediate DNA sequences Nextthe recombinase joins one VH region gene to the rearranged DHJHgene The enzyme terminal deoxynucleotidyl transferase (TdT) isexpressed adding random nucleotides to the sites of VHDHJHjoining and enhancing the diversity of amino acid sequences Therearranged VHDHJH element forms the most 51015840 exon of the Hchain gene and is followed downstream by exons encoding theconstant (C) region (initially 120583 chain) that pairs with an L chain andproduces IgMWhen theVHDHJHelement is followed downstreamby exons encoding the C region for the 120575 chain it produces IgDThese events occur as a result of alternative RNA splicing Finallyif the rearrangement of VH DH and JH elements yields an Hchain transcript and encodes a functional H chain protein thisheavy chain is synthesized and pairs in with 2 proteins (called1205825 and VpreB) which act as a surrogate light chain and resultsin the expression of a pre-BCR Once a functional heavy chainis produced the cell downregulates the TdT gene and initiates anL chain rearrangement It begins first with a 120581 element and ifthis rearrangement is unsuccessful continues with a 120582 elementA V120581 element rearranges to a J120581 element and produces a lightchain which if it is functional pairs with the H chain to make animmunoglobulin protein

Alternatively MZ B cells with mutated immunoglobulingenes but without activation-induced cytidine deaminase(AICDA) may have passed a germinal center (GC) response[15] Finally the expression of sphingosine 1-phosphatereceptor 1 on the B cells may overcome the recruiting activityof the B cell-attracting chemokine (BCA)-1 to the GCs [16]and thereby retain B cells within the MZ [17] (Figure 3) Themain CD molecules expressed by B cells are summarized inTable 2

24 Migration of B Cell into the Germinal Centers Organi-zation of the B cell follicles and surrounding T cell zones is

Table 2 Cell surface CDmolecules that are preferentially expressedby B cells

Name Cellular reactivity StructureCD19 Pan-B cell FDCs Ig superfamilyCD20 Mature B cells MS4A family

CD21 Mature B cells FDCs Complement receptorfamily

CD22 Mature B cells Ig superfamily

CD23 Activated B cells FDCsothers C-type lectin

CD24 Pan-B cell granulocytesepithelial cells GPI anchored

CD40 B cells epithelial cellsFDCs others TNF receptor

CD72 Pan-B cell C-type lectinCD79ab Surface Ig+ B cells Ig superfamilyFDCs follicular dendritic cells Ig immunoglobulin

achieved by the secretion of chemokines by distinct stromalcell subsets Of these subsets follicular dendritic cells (FDCs)are essential to retain immune complexes and produce B-lymphocyte chemoattractants (BLCCXCL13) FDC mainte-nance requires continual membrane expression of lympho-toxin 12057211205732 (LT12057211205732) trimer as well as TNF secretion byB cells and LT120573R and TNF-R1 expression on FDCs [18]The MZ demarcates the perimeter of the white pulp of thespleen and contains a subset of B cells that likely arises fromthe transitional B cell compartment [19] MZ B cells arestrategically located to respond to blood-borne antigens andcan rapidly differentiate into antibody-producing cells in thered pulp Upon an encounter with antigens follicular B cellsmigrate to the border regions of the PALScortex to presentbound peptide and costimulate T cells Reciprocal B cellactivation is mediated by engagement of CD40 and provisionof cytokine support CD40-dependent B cell activation isrequired to undergo proliferative expansion and differentia-tion in the GC where somatic hypermutation and enhancedimmunoglobulin class switch recombination (CSR) occurThe architecture of the GC is divided into distinct regionsrapidly dividing B cells or centroblasts in the ldquodark zonerdquo ofthe GC give rise to centrocytes which occupy the ldquolight zonerdquoThe light zone is thought to be the site of B cell selection byFDC-bound antigens that are processed and presented by Bcells to primed T cells of the follicular helper CD4+ (Tfh)subtype

B cell maturation in the GC is accompanied by somatichypermutation of antibody variable region (V) genes whichprovides the molecular basis for the production of B cellsbearing high-affinity antigen receptors These B cells arethought to have a competitive advantage when antigenbecomes limiting and GC structures present atrophy B cellsunable to bind antigen or receive sufficient T cell helpdie in situ by apoptosis and are cleared by macrophageswhereas antigen-selected B cells that leave the GC becomememory B cells or plasmablasts by a process that is not fullyunderstood Long-lived plasma cells are actively retained


Bone marrow-depelopment antigen-independent

Depelopment antigen-dependent

Plasma cell

MZ

Clonalexpansion

Clonalexpansion

Mem

LN

LN

Spleen

Lymphnode

Germinalcenter

SC Pre-pro Pro-B Lg-pre Sm-pre Imm

Mat

MZ

PreBCR IgM

TdTRAG1RAG2

MHCIICD19CD20CD21CD23CD40

IgM + IgD

Figure 2 B cell receptor development and differentiation

Germinalcenter

MZ B cell

High BCRsignal

Low BCRsignal

Sphingosine IP

BCA-1

Mutationswithout AID

T1 T2

Figure 3 B cell classification based on their ontogenic state Fromthe transitional type 1 (T1) and T2 B cells two options depend onthe B cell receptor (BCR) evoked signal and the downstreamNotch 2proteins germinal center (GC) B cells driven by the B cell-attracting(BCA)-1 chemokine (or CXCL13) andMZB cells withmutations butwithout activation-induced cytidine deaminase (AID) (Modifiedfrom [10])

in the BM responding to stromal derived factorCXCL12as well as survival factors such as IL-6 B cell activatingfactor (BAFF) and a proliferation-inducing ligand (APRIL)The trafficking of B cells in the lymphoid organs and target

tissues is a regulation mechanism of B cell activation anddifferentiation [20ndash22]

B cells can act as an antigen delivery system that trans-ports blood-borne antigens into the FDC network region ofthe spleen [17] This regulates the GC formation where highaffinity antibody-forming B cell differentiation occurs Thesemigratory responses are extremely dynamic and involveongoing shuttling of the B cells between the differentanatomic sites and theGCs Chemotactic responses play a keyrole in orchestrating the cell-cell interactions in the GCsThisprocess involves ongoing shuttling of the antigen-carryingB cells between the MZ and the GCs In animal modelsof autoimmunity the migration of MZ precursor B cells ispromoted by high levels of interferon (IFN)-120572 produced byplasmacytoid dendritic cells (pDC) in themarginal sinus thatantagonize the activity of the S1P1 chemokine receptor Incontrast within the GCs IL-17A upregulates the expressionof regulators of G protein signaling (RGS) in B cells todesensitize the G protein-coupled receptor (GPCR) signalingpathway of CXCL12 and CXCL13 chemokines [23ndash25] Thisprovides a prolonged stable interaction of B and T cells in theGC that induces high levels of AICDA and as a result enablesthe development of pathogenic autoantibody-producing Bcells (Figure 4)

25 Mature B Cells Peripheral B cell maturation home-ostasis and antigen-dependent differentiation are complexprocesses occurring in distinct anatomic locations As B cellsegress from the BM further maturation into follicular or MZB cells is dependent upon the effects of the cytokine BAFFB cell compartmentalization and cell-cell interactions in theSLO require expression of membrane-bound LT120572120573 trimers


BB

FDC

ShuttlingpDC

S1P in MZ

Marginal zone

Germinal center light zone

High affinityantibody-producing

B cell selectionCD4

DC69+DC86+Ag+

IFN120572 IL17

RgsCXCR5+

CXCR5+CXCL13

TH17

Figure 4 Chemotactic responses play a key role in orchestrating the cell-cell interactions in the germinal centers

Plasma cell

Plasma cell

Bm2

Mantle zone

Dark zone

Bm3

Bm4

Bm4

Bm5Bm4

T-cell zoneBm1

Follicle

Bm2998400

Figure 5 Germinal center (GC) changing a primary lymphoid follicle (LF) into a secondary LF The GC is surrounded by the mantle zonewhich is comprised of the light and dark zone and populated by mature B (Bm) cells evolving from Bm1 in the T cell area through plasmacells that come back to the bone marrow

and TNF whereas T cell-dependent B cell differentiationrequires engagement of CD40 (TNFRSF5) by CD40L onactivated CD4+ T cells CD30 (TNFRSF8) is expressed onactivated B cells and has been found to be required forefficient memory B cell generation CD27 is also implicatedin B cell memory

The development stages of GC B cells are based on therelative expression of IgD and CD38 on mature B (Bm)lymphocytes [26] from naıve cells leaving the BM (Bm1) tomemory B cells activated and differentiated by their specificantigen (Bm5) The development starts with CD38minusIgD+naıve Bm1 that progresses into CD38+IgD+ antigen activatedBm2 of which some becomeCD38++IgD+Bm21015840 GC foundercells These differentiate into CD38++IgDminusBm3 centroblastsand Bm4 centrocytes (Figure 5) Two types of B cells arise

from GC reactions CD38+IgDminus early memory B cells thatmature locally into CD38minusIgDminusBm5 memory B cells andCD38++IgDminus plasmablasts which were first described byOdendahl et al [27] The latter return to the BM where theydifferentiate into long-lived plasma cells A few cells of eachsubset escape into the circulation from GCs

26 B Cell Distribution Abnormalities in Systemic LupusErythematosus Several studies show differences of certainperipheral B cell subsets in SLE patients compared tohealthy controls Populations such as transitional B cells(CD24++CD38++) prenaıve and naıve B cells are expandedin the peripheral blood of patients [28] indicating a popula-tion shift within the preimmune B cell compartment towardthe more immature B cells Whether these abnormalities


reflect an intrinsic B cell defect or are secondary to inflam-mation or immune deregulation is unclear but the excess ofsome cytokines such as BAFFmay explain part of these differ-ences In peripheral blood of healthy controls transitional Bcells account for only 2 to 3 of all B cells [29 30] In contrastSLE patients have an increased frequency of approximately6-7 This high proportion does not correlate with diseaseactivity and titres of autoantibodies Due to the lymphopeniaseen in SLE patients the absolute number of transitional Bcells is not different to that of controls The most importantcheck point in SLE seems to be at the transitional stageHigh number of self-reactive mature naıve B cells whichsubsequently originate autoantibody producing plasma cellsThis is the most reported characteristic of the abnormal Bcell homeostasis in SLE characterized by the expansion ofperipheral CD27++ plasmablasts [31] which also correlateswith disease activity and the titre of autoantibodies [32] Onthe other hand the frequency of CD19+CD27+ memory Bcells seems to be unaffected in SLE patients with active andinactive disease although the total number ofmemory B cellsis decreased in SLE patients compared to healthy controls[27]

27 B Cell Derived Cytokines IL-7 is important in B cellfunctioning This cytokine plays several important roles dur-ing B cell development including aiding in the specificationand commitment of cells to the B lineage the proliferationand survival of B cell progenitors and maturation duringthe pro-B to pre-B cell transition [33] Regulation andmodulation of IL-7 receptor (IL-7R) signaling is criticalduring B lymphopoiesis because excessive or deficient IL-7Rsignaling leads to abnormal or inhibited B cell development[34] IL-7 works together with E2A EBF Pax-5 and othertranscription factors to regulate B cell commitment whileit also works to regulate immunoglobulin rearrangementby modulating FoxO protein activation and Rag enhanceractivity Suppressors of cytokine signaling (SOCS) proteinsare inhibitors of cytokine activation and in B cells functionto fine-tune IL-7R signaling This ensures that appropriateIL-7 signals are transmitted to allow for efficient B cellcommitment and development [35]

Recent discoveries have unveiled new insights into B cellderived cytokines including IFN-120574 and IL-4 that modulatethe response [36] They are likely to serve as effectors ofsome B cell functions Given the kinetics of B cell generationand the cytokine profile of B lymphocytes T helper (Th)1 phenotype may be imprinted by B effector (Be) 1 cellsthrough the expression of IL-2 and IFN-120574 by B cells Thisis sustained by an IFN-120574IFN-120574 receptor autocrine loopConversely Th2 cells induced naıve B cell polarization intoBe2 which produces IL-4 and IL-6 in the absence of GATA-3 In fact the Th1Th2 cytokine balance changes with theprogress of the immunopathological lesions on autoimmunediseases such as SLE and primary Sjogrenrsquos syndrome [37]Distinct populations of serum cytokines have also beenfound to differentiate autoimmune disease patients fromcontrols and one patient from another depending on thepresence or absence of different organ involvement [38] Bcell produced cytokinesmay be classified as proinflammatory

(IL-1 IL-6 TNF-120572 and LT-120572) immunosuppressive cytokines(TGF-120572 and IL-10) or as hematopoietic growth factors(granulocytemonocytes-colony stimulating factor and IL-17)

28 B Cell Transcription Factors B cell development dependson several transcription factors One of the most importanttranscription factors isPax5Pax5 restricts the developmentalpotential of lymphoid progenitors to the B cell pathway byrepressing B-lineage-inappropriate genes while it simultane-ously promotes B cell development by activating B-lymphoid-specific genes Therefore Pax5 controls gene transcriptionby recruiting chromatin-remodeling histonemodifying andbasal transcription factor complexes to their target genes[39] Moreover Pax5 contributes to the diversity of theantibody repertoire by controlling VH-DJH recombinationIt does this by inducing contraction of the immunoglobulinheavy-chain locus in pro-B cells which is likely mediatedby PAIR elements in the 50 region of the VH gene clusterImportantly all mature B cell types depend on Pax5 fortheir differentiation and function Pax5 thus controls theidentity of B lymphocytes throughout B cell developmentConsequently conditional loss of Pax5 allows mature B cellsfrom peripheral lymphoid organs to develop into functionalT cells in the thymus via differentiation to uncommittedprogenitors in the BM Pax5 has also been implicated in somediseases including human B cell malignancies

3 B Cell Tolerance Mechanisms andTheir Role in Autoimmunity

31 B cell Tolerance This mechanism is essential for main-taining nonresponsiveness to thymus-independent self-anti-gens such as lipids and polysaccharides B cell tolerance isalso important in preventing the development of antibodyresponses to protein antigens Both central and peripheralmechanisms are implicated in B cell tolerance In the centraltolerance the immature B lymphocytes that recognize self-antigens in the BM with high affinity are deleted or activatemechanisms to change their specificity by receptor editingThis fate is defined by the strength of BCR signaling a strongBCR signal by binding with high affinity to an autoantigenwill lead to deletion or receptor editing (see below) while anintermediate binding affinitywill permit B cells to survive andcontinue to the periphery [40]

If a mature B cell recognizes autoantigens in peripheraltissues without specific helper T cell response this cell maybe functionally inactivated by anergy mechanisms or dieby apoptosis The AICDA is required for B cell tolerancein humans This enzyme is required for CSR and somatichypermutation Patients withAICDAdeficit develop primaryimmunodeficiencies and autoimmune complications SingleB cells from AICDA-deficient patients show an abnormalimmunoglobulin (Ig) repertoire and high frequencies ofautoreactive antibodies [41]

32 B Cell Receptor Editing When the B cell differentiationis ongoing its receptor presents a phenomenon known as


receptor editing which is the process of antibody generearrangement to have a functional BCR and inhibit furtherrearrangement (allelic exclusion) The receptor editing isa major mechanism of central tolerance in B cells If aT lymphocyte produces a self-reactive receptor differentmechanisms are initiated to induce the apoptosis of thisself-reactive cell (negative regulation) However B cells havea second chance at escaping this negative regulation byldquoeditingrdquo the specificities of their receptors with additionalantibody gene rearrangements Immature B cells in theBM that encounter multivalent self-antigens revert to pre-Bstage and continue to rearrange 120581 and if necessary 120582 lightchain genes and generate newly generated B cells that havea novel light chain that is no longer self-reactive In thiscase immature B cells with novel light chains that are nolonger part of a self-reactive BCR migrate to the peripheryas BT1 cells where they mature into newly generated IgMand IgD expressing recirculating BT2 cells and then intomature recirculating B cells Furthermore edited B cells arenot simply endowed for life with a single invariant antigenreceptor because an edited B cell whose initial Ig gene isnot inactivated during the editing process may exhibit twospecificities [42]

The BCR editing process initiates with the allelic exclu-sion This is the phenomenon in which B cells usuallyexpress a single kind of antibody H chain and L chain andit is typically enforced at the genetic level with only oneallele being productively rearranged A series of epigeneticmechanisms including replication timing DNA methyla-tion histone modification nucleosome positioning andheterochromatization appear to control H and L chain locusaccessibility and which allele is first rearranged [43] Thesemechanisms regulate accessibility to recombination machin-ery and activate feedback inhibition of the rearrangementbetween H chain and L chains Once the H chain proteinis completed L chain rearrangements initiate This processis regulated by isotypic exclusion a phenomenon in whichB cells usually express a single L chain isotype (either 120581 or120582 not both) and is explained by two properties of L chainrearrangement first the 120581 or 120582 rearrange at different timesduring B cell development and second the B cells whichexpress 120582 often have both 120581 alleles deleted Based on theanalysis of cell lines in mouse and human it was clear that120581 chain nearly always rearranges before 120582 chain [44 45]

Another process identified is the secondary rearrange-ment of H and L chains In heavy chain the mechanismis mediated by DH-JH rearrangement DH-DH fusion andVH replacement all of which contribute to the elongation ofthe third complementarity determining region (CDR3) andpromote autoreactivity During DH-JH rearrangement a DHgene upstream of the existing DH-JH rearrangement recom-bines with a JH gene downstream of the DH-JH rearrange-ment and replaces it by a leapfrogging deletion rearrange-ment In a DH-DH fusion the recombination process links a51015840 DH segment to a preceding DH-JH rearrangement ratherthan to a 31015840 JH gene DH-DH fusion occurs more frequentlyin murine lupus than in nonautoimmune strains of mice[46 47] Finally during VH replacement the conventional 23recombination signal sequence (RSS) of an upstreammurine

VH undergoes RAG-dependent deletional rearrangementwith the cryptic RSS of an existing downstream VH genewhich is part of an existing VDJ rearrangement on the sameallele This rearrangement results in replacement of all butthe very 31015840 end of the previously rearranged VH with a newVH Secondary rearrangement which would consist of eitherdeletion or inversion of the chromosomal DNA between therecombining gene segments can also occur at the 120581 locusThese rearrangements are apparently part of an importantphysiological process underlying failed allelic exclusion andmight occur to edit the specificity of a self-reactive BCR(Figure 6)

33 Control of Receptor Editing Receptor editing has agenetic control and has been studied in several models Pre-B cells expressing I120581B show evidence of receptor editingwhich is consistent with a role for NF120581B [48] PLC1205742 ispresent in higher quantities in immature B cells showingincreased phosphorylation in response to BCR crosslinkingand probably induces the expression of Rag2 in these cellsHowever other data show downregulation of rag inducedby PLC1205742 and thus terminate receptor editing ImmatureB cells can be induced to edit by BCR crosslinking whiletransitional B cells cannot This may be due to an alteredsignaling pathway through PLC1205742 [49 50]

Themechanisms that suppress editing and their potentialrole in autoimmune diseases are under research

34 BCell andAutoimmunity Classically the immunemech-anisms implicated in the development of autoimmune dis-eases have been categorized into two broad sets of diseasesone set in which the pathological process is driven by T cellsand the other in which the humoral B response mediates thedisorder by producing autoantibodies that are able to bind tis-sue self-antigens or by forming immune complexes In recentyears with the new knowledge about the immune responsethis approachmdashdividing autoimmune diseases into T cell andB cell mediated diseasesmdashhas dramatically changed It is nowrecognized that T lymphocytes facilitate adaptive immune Bresponses and B cells play a reciprocal role during CD4 T cellactivation in autoimmune diseases

For instance most disease-related autoantibodies areIgGs that are somatically mutated and this suggests thathelper T cells drive the autoimmune B cell response [51] Inaddition B cells have been shown to be important mediatorsof some autoimmune diseasesThese are classically describedas T cell mediated and include rheumatoid arthritis (RA)multiple sclerosis (MS) and type 1 diabetes mellitus (T1D)In diseases in which specific autoimmune T cell clones drivethe process of inflammation autoantibody synthesis mayrepresent a marker for the expansion of autoantigen specificB cells that capture and present autoantigen peptides to Tcells As mentioned before the central tolerance mechanismsare crucial in preventing B cell mediated autoimmune dis-eases For instance the strong BCR signal from bindingwith high affinity to an autoantigen will lead to deletionor receptor editing of the high affinity This concept hasbeen demonstrated in several autoimmune animal modelsincluding a double-transgenic mouse model carrying not


Bone marrow Spleen

Small pre-B Immature B T1 T2 Mature B

IgMIgDPeriphericalcheckpoint

Centralcheckpoint

Multivalent self-antigen

Figure 6 Receptor editing as a major mechanism of central tolerance in B cells Receptor editing is a major mechanism of central tolerancein B cells Immature B cells in the bone marrow that encounter multivalent self-antigens revert to the small pre-B stage continue to rearrangek and if necessary l light chain genes and generate newly B cells that have a novel light chain that is no longer self-reactive Immature B cellswith novel light chains that are no longer part of a self-reactive B cell receptor then migrate to the periphery as T1 B cells where they matureinto newly generated IgM and IgD expressing recirculating T2 B cells and then into mature recirculating B cells

only the heavy chain against the myelin oligodendrocyteglycoprotein (MOG) autoantigen but also the light chainTheauthors demonstrated that B cells expressing solely theMOG-specific Ig H chain differentiate without tolerance On theother hand double-transgenic B cells expressing transgenicIg H and L chains are subjected to receptor editing [52 53]

If the signaling potential of the BCR is affected for exam-ple by overexpression of CD19 or Ptpn22 polymorphisms(described in several autoimmune diseases) the self-reactiveB cells will not be deleted and may reach the periphery[54 55] These mechanisms lead to the increase of self-reactive B cells in the periphery and as a consequence thepossibility of developing autoimmune diseases Thus leakycentral tolerance increases the risk for subsequent develop-ment of autoimmune disease but additional factors (genetichormonal environmental etc) control this progression fromautoimmunity to autoimmune disease

The role of Toll-like receptors (TLR) in B cell andautoimmunity has also been explored In a study to determinethe stimuli contributing to the development into MZ B cells(involved in autoimmunity) TLR9 stimulation by CpG oftransitional B cells induces proliferation and specific matura-tion into B cells with phenotypic markers of MZ B cells Alsothe terminal differentiation into antibody-secreting cell wastriggered leading to autoantibodies synthesis On the otherhand mature B cells do not differentiate into MZ followingTLR9 stimulation These results suggest that transitional Bcells are specifically sensitive to TLR9 stimulation to induceautoreactive B cells [56]

35 B Cell Functions in Autoimmunity B cells do not simplyproduce autoantibodies In fact B lymphocytes are uniquelyendowed to drive autoimmunity as APC because they canbind native self-proteins through their BCR process themand present them to T lymphocytes To demonstrate theantigen-presenting effect of B cells in autoimmunity severalmodels and observations have been used For example in

the murine experimental allergic encephalomyelitis (EAE)B lymphocytes are dispensable when disease is induced byMOG peptides but absolutely required for disease to developif mice are immunized with MOG protein [57] In MOG-specific TCR and BCR double-transgenic mice self-reactiveB cells cause severe EAE by presenting endogenous MOGprotein to self-reactive T cells rather than by autoantibodyproduction [58 59] In addition to this observation in EAE (aclassical described T cell disease) B cell depletion by ritux-imab strongly reduced disease severity affecting the delayedtype hypersensitivity and reducing T cell proliferation andIL-17 production [60] The IL-6 seems important to mediatethese effects as indicated by the findings that rituximab effectsare not observed in IL-6 KO mice with EAE

Another example to show that B cells functions in au-toimmunity are not only producing autoantibodies is thetransgenic mIgMMRL-FASlpr mouse In this model whoseB lymphocytes cannot secrete antibodies but can presentantigen lupus develops spontaneously and T cell activationis comparable to MRLlpr controls [61] Likewise nonobesediabetic (NOD) mice with a mutant IgM heavy chain thatcannot be secreted demonstrate that increased insulitis andspontaneous diabetes may occur in the absence of antibodyproduction but require antigen presentation by B cells [62]

The ability of B cells to bind autoantigens through theirBCR allows them to act as potent APCs at very low proteinconcentrations In the MOG-specific TCR and BCR double-transgenic mice antigen specific B cells process and presentMOG protein to T cells at concentrations that are 100-fold lower than B cells with other BCR specificities Otherfunctions of B cells are cytokine and chemokine synthesis andectopic lymphoid neogenesis in autoimmune diseases

36 Amplification of the Autoimmune Response by EpitopeSpreading B cells bind to a specific epitope in antigens viatheir BCR After the initial recognition protein and even pro-tein complexes can be internalized and processed for antigen


presentationThe proteinmay however contain several otherepitopes besides the epitope originally recognized by theBCR which can fit in the binding grooves of the MHCIImolecules in the B cell As a consequence the B cells canpresent not only the original epitope but also other epitopesof the same protein or protein complex to T lymphocytes andthereby trigger different T cell specificities [63] This phe-nomenon known as epitope spreading allows autoantigensthat were not the initial targets of autoreactive lymphocytesat the onset of autoimmunity to become antigens at laterstages [64] This phenomenon is described in almost allimmune diseases and is frequently associated with diseaseprogression [64] Epitope spreadingmay trigger the clinicallymanifested autoimmunedisease As a representative examplethe SJLJ mice immunized with protelipid (PLP) proteinsdevelop T cell responses specific to different epitopes inthe molecule These distinct T cell responses contributeto the relapse phases of the EAE and can initiate diseaseupon secondary adoptive transfer to naıve animals [65]Epitope spreading also occurs in the NOD mouse model ofspontaneous diabetes In this model T cell responses andantibodies to type 1 diabetes (T1D) autoantigens GAD65 andGAD67 isoforms of GAD are observed in mice at 4 weeksof age At 6 weeks of age T and B lymphocyte responses forother 120573 cell antigensmdashperipherin carboxypeptidase H andHsp60mdashare also detected By 8 weeks of age responses toall former antigens are enhanced The initial GAD specificreactivity in this model coincides with the onset of insulitiswhereas the progression of insulitis to 120573 cell destruction withage correlates to the epitope spreading of B and T cells [66]Temporal progression of autoreactivity to autoimmune dis-ease by epitope spreading also occurs in human autoimmunediseases In childhood T1D diabetes insulin autoantibodies(IAA) are the first autoantibodies detected IAA-positivechildren that sequentially develop antibodies to other 120573 cellantigens such as GAD and protein tyrosine phosphatase-likeproteins IA-2 usually progress to T1D In contrast childrenthat remain positive for only IAAs rarely develop the disease[67] In RA several reports have shown that the number ofantibody specificities increases over time Like T1D patientshealthy individuals with a broad anticitrullinated peptideantibody (ACPA) profile have a higher risk of developingarthritis [64 68] This phenomenon is also observed in SLEpatients In this case the number of positive antibodies inserums of patients also increases over time until the onset ofclinical symptoms as demonstrated in the classic article aboutautoimmune diseases prediction by Arbuckle et al [69]

37 The Effects of the Cytokine BAFF in B Cell Tolerance andSLE Development The cytokine BAFF (for B cell activatingfactor belonging to the TNF family) has emerged since1999 [70] as one of the critical factors controlling B cellmaturation tolerance andmalignancy BAFF plays a key rolein B cell differentiation survival and activation [70] BAFFalso known as B lymphocyte stimulator (BLyS) is a cytokinethat prevents apoptosis of autoreactive B cells [21] The BAFFfamily consists of two ligands a proliferation-inducing ligand(APRIL) and BAFF and three membrane receptors BCMA(B cell maturation antigen) TACI (transmembrane activator

BAFF APRIL

BR3 BCMA TACI Proteoglycans

Figure 7 BAFF and APRIL receptors BAFF binds chiefly to BAFF-R (BR3) but also to BCMA and TACI APRIL in turn interactswith TACI and BCMA but not with BR3 In addition APRILbinds to proteoglycans expressed in membranes of lymphoid andnonlymphoid cells

calcium modulator and cyclophylin ligand interactor) andBAFF-R (also known as BR3) The interactions betweenligands and receptors vary thus BAFF interacts chiefly withBR3 but can interact with all three receptors whereas APRILcan interact with TACI and BCMA but not with BR3 [71]BAFF enhances B cell survival drives B cell maturationespecially at the early transitional stages and discontinueshumoral tolerance by rescuing autoreactive B cells fromapoptosis [72] Figure 7 shows the different receptors forBAFF and APRIL

38 Double-Transgenic Mice Expressing Both HEL and Anti-HEL B Cell Receptor As mentioned before to avoid the gen-eration of pathogenic autoantibodies self-reactive lympho-cytes have to be deleted or anergized at successive immunecheckpoints during B cell development and maturationBecause immunoglobulin gene rearrangement is a randommechanism 50ndash75 of the newly generated B cells in theBM have a self-reactive BCR However the developmentof autoimmune disease is rare affecting up to 5 of thepopulation Consequently effective mechanisms exist forpreventing immune activation of self-reactive lymphocytesBAFF is known for its role in the survival of mature Bcells Based on its receptor expression profile BAFF has noeffect on B cell tolerance in the BM but does act at theperiphery (Figure 8) BAFF certainly plays a major role in Bcell tolerance after the BT1 immature B cell stage Whether ornot BAFF can influence self-reactive BT1 cell elimination isunclear However BAFF is certainly needed for the survivalof BT2 cells and downstream B cell subsets BT2 cells whichexpress high levels of BAFF-R are indeed dependent onBAFF because of their propensity for apoptosis [73] and Bcell ontogenesis is stopped at the T1 stage when BAFF orBAFF-R are lacking [74]One of themost informative systemsfor studying B cell tolerance is the double-transgenic (Tg)mouse model which expresses the anti-hen-egg lysozyme(HEL)BCRandHEL simultaneouslyWhenHEL is expressedas a cell surface molecule self-reactive B cells are deleted orundergo additional ig gene rearrangements by the receptorediting mechanisms When HEL is expressed as a soluble


BAFF

Plasma cell

ImmatureB-Cell

migM

Pre B cell T1 B cell T2 B cell

IgM

Plasma cell

Fo B cell

MZ B cell

Spleen marginal zone

GC75 self-reactive

15 self-reactive

BR3TACI

BCMA

Acting on differentiationActing on survivalCheckpoint

35 self-reactive

Bone marrow Periphery

Figure 8 BAFF receptor cell surface expression and self-tolerance during B cell ontogenesis Data indicate the proportion of self-reactive Bcells at specific B cell stages before or after checkpoints as determined in the anti-HELHEL transgenic models Fo follicular GC germinalcenter Imm immature MZ marginal zone Pre precursor T1 or 2 transitional type 1 or 2

protein (sHEL) self-reactive B cells can migrate into theperipherywhere their fate depends on their ability to competewith non-self-reactive B cells Without competition self-reactive BT2 cells persist in an anergic state In the presenceof competition self-reactive BT2 cells need the cytokineBAFF to sustain their survival and maturation BecauseBAFF levels are limited under normal conditions these self-reactive B cells undergo apoptosisThus if double Tgmice forsHELanti-HEL are treatedwith antagonist for BAFF survivalof sHEL self-reactive B cells is dramatically decreased [75]In contrast when BAFF is overexpressed sHEL self-reactiveBT2 cells survive and colonize follicles and MZ in the spleen[76] Of note when anti-HEL B cells compete with normal Bcells in the animal excessive expression of BAFF no longerprevents the escape of self-reactive B cells In this scenarioself-reactive cells are eliminated at a much earlier maturationstage (T1) a stage when B cells express little BAFF-R and assuch are unable to sense excessive BAFF production that canonly efficiently rescue BT2 cells

39 BAFF-Transgenic Mice BAFF-Tg mice constitute aneffective model for autoimmunity Overproduction of BAFFin these mice leads to B cell proliferation auto-antibodyproduction and ultimately development of kidney fail-ure similar to SLE-associated symptoms Moreover agingBAFF-Tg mice also present a primary Sjogrenrsquos syndrome-like disease in which they demonstrate inflammation anddestruction of salivary glands (SGs) [72] In addition tothe attendant polyclonal hypergammaglobulinemia BAFF-Tg mice develop elevated titers of multiple autoantibod-ies including antinuclear antibodies anti-double-strandedDNA rheumatoid factors circulating immune complexesand immunoglobulin deposits in kidneys SomeB cell subsets

such as BT2 cells follicular (Fo) B cells and MZ B cellsrise Moreover without stimulation a high number of GCsare found in the spleen and the lymph nodes Finallylymphocytes infiltrating the SG are essentially MZ-like Bcells Note that BAFF-Tg mice develop the same pSS mani-festations when T cells are removed [77] but in this instanceBAFF exacerbates Toll-like receptor activation of B cells Analternativemodel for the development of SS apart fromT cellshas since been proposed [78]

310 CD5 in Its Implications in Autoimmunity The CD5 isa transmembrane glycoprotein expressed in T lymphocytesand at lower levels in the subset of B cells known as B1cell The initial interest on CD5+ expressing B cells pointedon the role of these cells in autoimmune diseases basedon the ability of these cells to produce natural polyreactiveantibodies which recognize autoantigens with low affinity[79 80] The hypothesis in autoimmune diseases was thatthese natural antibodies with low affinity to autoantigensmayimprove this affinity and become in high affinity pathogenicautoantibodies However the B1 cells expressing CD5 havephenotypic features similar to transitional anergic murineB lymphocytes In fact these cells may produce IL-10 uponactivation through the CD40 coreceptor [81 82] The regu-latory potential of CD5 has been demonstrated by transfec-tions of CD5 in Jok-1 B cell line [83] In this experimentthe expression of CD5 induces IL-10 production throughactivating NFAT2 and STAT3 Thus CD5-expressing B cellsmay present contradictory roles in B lymphocytes functionAn elegant study showing how CD5 expression is regulatedin B lymphocytes and how it modulates the B cell responsehas been published This study analyzed the molecularstructure of the human CD5 gene showing that two different


promoters exist (E1A and E1B) [84]TheE1B Interestingly theCD5-E1A was expressed on the membranes of both T andB lymphocytes while the CD5-E1B was transcribed into atruncated CD5 isoform in B lymphocytes not able to expresson the membranes CD5-E1B expression downregulates thelevel of membrane expression of the conventional CD5-C1AAs a consequence high levels of CD5-E1B could reduce theinhibitory effects of CD5 onBCRmediated signaling and leadto increased antibody production Thus in B cells expressinghigh or normal levels of membrane CD5 the molecule actsto downregulate BCRmediated signaling On the other handB cells expressing high levels of CD5-E1B induced probablyby external stimuli would more likely to be activated Tosupport these results in B lymphocytes fromSLEpatients thelevels of CD5-E1B are higher indicating a more activating Bcell [85] These high levels of CD5-E1B traduces in reducedexpression of membrane CD5 In this model high levelsof IL-6 on B cells from SLE patients abrogate the abilityto induce the DNA methyl transferase (DNMT1) and thento methylate DNA affecting the transcription of CD5-E1Afavoring the truncated form E1BThis altered signaling couldpromote the activation and expansion of autoreactive B cellsin SLE patients Interestingly in mature B cells from SLEpatients a default in the regulation of Rag is present andleads to upregulation of this enzyme and the emergence ofautoantibodies [86 87] CD5 and IL-6 contribute to thisupregulation indicating the roles of these molecules in SLEpathogenesis

In murine models CD5 is involved in anergy [88] Thishypothesis has been elegantly demonstrated breeding theHEL transgenic model for B cell anergy onto the CD5null background This experiment resulted in a spontaneousloss of B cell tolerance in vivo The study showed highlevels of anti-HEL IgM antibodies and enhanced proliferativeresponses in vitro with elevated intracellular calcium levels

311 CD22 in Its Implications in Autoimmunity Anotherimportant B cell molecule which has an effect on autoimmu-nity development is the CD22 B cell responses are initiatedby antigen binding to the BCR and are modified by abroad repertoire of activating and inhibitory transmembranecoreceptors expressed on the B cell surface [89 90] Inthis context the multifunctional BCR co-receptor CD22 isinteresting since it plays a critical role in establishing andmodulating the antigen receptor signaling thresholds for Bcell activation [91] CD22 as part of the BCR complex canmodulate the intensity quality and duration of homeostaticand BCR-induced signals in an inhibitory or stimulatorycapacity through ligand-dependent and -independent mech-anisms [92 93] Based on substantial mouse model data itappears that the predominant effect of CD22 is inhibitory[94] CD22 is a 135 kDa B lymphocyte restricted type-Itransmembrane sialoglycoprotein of the immunoglobulinsuperfamily [95] It appears intracellularly during the latepro-B cell stage of ontogeny but shifts to the plasma mem-brane with B cell maturation CD22 is expressed at lowlevels on immature B cells and at higher levels on matureIgM+ IgD+ B cells However it is absent on differentiatedplasma cells It is strongly expressed in follicular mantle

and marginal zone B cells but is weakly present in germinalB cells [96] As previously mentioned for the immunesystem to function effectively it is essential to mount anappropriate humoral response against potential pathogenswhile avoiding autoimmunity and reactivity to self-antigens[97] Understanding the function of CD22 may thereforesuggest methods for modulating humoral immunity and aidin discovering treatments for autoimmunity [98]

To regulate B lymphocyte functions and migration theinteraction of CD22 with 12057226-linked sialic acid ligands isimportant This binding is necessary for its negative regula-tory functions [99] Cell lines expressing CD22 without sialicacidbinding activity are hyperresponsive to BCR stimulation[99]

Recent studies in mouse models have suggested a role fordefects and loss of functionality in CD22 in the pathogenesisof autoimmune disease including SLE B cells obtained fromCD22-deficient mice have been shown to be hyperresponsiveto receptor signaling and demonstrate increased Ca2+ fluxeson BCR ligation which increased serum titers of IgG anti-dsDNA autoantibodiesThese antibodies were of multiclonalorigin were somatically mutated and had high affinity [100]

Epratuzumab is a novel humanized antihuman CD22IgG1 monoclonal antibody that binds to the extracellulardomain of CD22 and induces modest but significant intra-cellular phosphorylation Epratuzumab reduces total blood Bcells by about 35ndash40 and has preferential effects on naıveand transitional B cells [101 102] Epratuzumab treatment hasbeen used with moderate clinical success in SLE and primarySjogrenrsquos syndrome [103]

312 A New Concept in Autoimmunity Regulatory B Cells Afunctional B cell subset called regulatory B cells has recentlyemerged as an important factor for maintaining immunetolerance This subtype restrains the excessive inflammatoryresponse that occurs during the development of autoimmunediseases The main regulatory B cell function is mediated bythe IL-10 production that inhibits proinflammatory cytokinesand supports regulatory T cell differentiationThe regulatoryB cells were named in 2002 [104] after the demonstration thatIL-10 producing B cells can suppress inflammatory responsesin experimental autoimmune encephalomyelitis collagen-induced arthritis and autoimmune colitis [105 106]

In the murine models regulatory B cells have also beenshown to directly inhibit T cell proliferation through cell-cellcontact This may even lead to anergy or apoptosis of T cells[107 108] and the modulation of the inflammatory responseIn this regard CD40 engagement on B cells appears to be arequisite for the induction of functional B regulatory cells inmice Stimulation of CD40 brings about the development ofB cells with suppressive properties Furthermore signalingin the absence of CD40 makes B cells unable to regulateinflammatory response [105 109]

The murine phenotypic nature of B regulatory cells isstill a matter for debate Two distinct IL-10 producing Bcell subpopulations associatedwith regulatory functions havebeen identified One has been recognized as transitionalmarginal zone precursor B cells expressing a high level ofCD21 CD23 CD24 IgM and CD1d designed as transitional


type 2 (T2)-like cells [110ndash112] The secondmdashdescribed asCD1dhi CD5+ and CD19hi B cellsmdashhas been called ldquoB10rdquocells since IL-10 is the main cytokine produced by these cells[81] Recent studies have suggested that human B cells canalso regulate inflammatory responses [113] These cells havebeen studied primarily in autoimmune diseases includingSLE and multiple sclerosis for which functional as well asnumerical defects of these cells have been described [112 114ndash116] A recent publication on patients with SLE describeda population of regulatory CD19+CD24++CD38++ B cells[112] as a phenotype reminiscent of preimmune B cells Thissubset is able to secrete IL-10 and thus is able to suppress Th1andTh2 functions after activationThese cells though presentin numbers similar to controls lack regulatory capacity inSLE patients

In addition to the described results another study onhuman regulatory B cells showed that regulation of T cellproliferation was defective in SLE patients but not in otherautoimmune diseases [117] This paper studied the regu-lation of T cell responses induced by B cells followingCD40 cognate interaction CD40-induced regulatory B cellspartially inhibited T cell proliferation without any solu-ble factor In contrast modulation of Th1 differentiationresulted from CD80- and CD86-dependent interactions andIL-10 production The suppressive effects were mediatedby CD19++IgD+CD38++CD24++CD5++ and appeared tobe indirect through the induction of regulatory T cells(CD4+CD25+FoxP3+) The mentioned defect of B cell reg-ulatory effect was found only in SLE patients indicating thatthe restoration of efficient B cell regulatory activity could bean innovative and alternative therapy in SLE

In another interesting paper from the same group theeffects of human B cells with a regulatory potential ondendritic cells have been studied In an in vitro model ofcocultures human activated B cells (CD19+IgDlowCD38+CD24lowCD27minus) showed a potential to restrain the develop-ment of monocytes into immature dendritic cells and theirdifferentiation intomature dendritic cell decreased theHLA-DR CD80 and CD86 expression and the production of IL-12p70 required for antigen presentation and Th1 differen-tiation [118 119] Even more interesting mature dendriticcells from patients with SLE displayed insensitivity to theregulation of IL-12 induced by B cells Thus inefficient Bcell regulation may alter the balance between an effectorinflammatory response and tolerance induction

Knowledge about these cells is increasing rapidly butmuch remains to be understood regarding the biology ofB regulatory cells in murine models and humans Theincreasing knowledge may allow the development of targetedtherapies in order to increase the B cell regulatory function inautoimmune diseases

313 B Cell Targeted Therapies in SLE Several B cell mole-cules can be targeted to treat autoimmune diseases (Table 3)The most widely studied target for achieving B cell depletionin autoimmune disease is the CD20 antigen (human B cell-restricted differentiation antigen) a hydrophobic transmem-brane protein with a molecular weight of approximately35 kDa found on pre-B and mature B cells [120 121] as well

Table 3 Potential targets in B lymphocytes and the therapeuticmolecule for the treatment of systemic lupus erythematosus

Direct B lymphocyte targetingCD-20 antigen(i) Rituximab (chimeric monoclonal antibody) EXPLORER andLUNAR studies did not meet primary endpoints(ii) Ocrelizumab (humanized monoclonal antibody) phase IIprematurely stopped due to infections(iii) Ofatumumab (human monoclonal antibody) no studies inSLE(iv) Veltuzumab (humanized monoclonal antibody) no studies inSLE(v) TRU-015 (engineered protein)CD-22 antigen(i) Epratuzumab (humanized monoclonal antibody anti-CD22)phase III study ongoingIndirect B lymphocyte targetingBAFF(i) Belimumab (LimphoStat B fully human monoclonal antibodyanti-BAFF) FDA approved based on BLISS 52BLISS 76 phase IIIstudiesBAFF receptors(i) Anti-BR3(ii) Atacicept (fusion IgG with the extracellular domain of TACIreceptor) study in progress(iii) BriobaceptBR3-Fc (fusion IgG with the extracellular domainof BAFF receptormdashBR3)BAFF B lymphocyte Activator Factor belonging to the TNF family TACItransmembrane activator and calcium modulator and cyclophylin ligandinteractor

as in over 90 of the B cells in NHL [122] Pilot studies ofan anti-CD20 antibody (rituximab) in SLE were promising[123 124] A review of off-label use also suggested signif-icant clinical and serological response [125] However tworandomized trials showed no superiority of rituximab overstandard therapy and did not reach primary or secondary endpoints [126 127] Despite these overall discouraging resultsboth studies have significant design shortcomings that limittheir applicability A study with another anti-CD20 antibodyocrelizumab was stopped prematurely due to an increaseof serious infections As mentioned above CD22 inhibitionwith epratuzumab may be an alternative for B cell inhibitionin SLE A phase III study is now undergoing [128]

Another therapeutic approach is the inhibition of BAFFeffects on B cell This inhibition can be done by anti-BAFFor anti-BR3 monoclonal Abs as well as BR3 or TACI decoyfusion proteins Selective BAFF blockers prevent BAFF frominteracting with its receptors leaving APRIL available tointeract with TACI and BCMA Drugs in this class includeanti-BAFF Ab (Belimumab or LymphoStat B) and a fusionprotein consisting of human Ig Fc and of the extracellularBR3domain (Briobacept for BAFF-R-Ig)Nonselective BAFFblockers abolish the interactions of both BAFF and APRILwith all their receptors To date there is a single drug in thisclass which is human Ig Fc fused to the extracellular TACI


domain (Atacicept TACI-Ig) Differences in the distributionof the forms of BAFF could denote the potential of patientsto respond or to resist to BAFF antagonist therapy Treatmentof B cells with TACI agonist Ab inhibits proliferation in vitroand activation of a chimeric receptor containing TACI intra-cellular domain induces apoptosisThese results demonstratealso the critical requirement for TACI in regulating B cellhomeostasis The therapeutic effects of anti-BAFF therapywith Belimumab have been demonstrated in patients withSLE based on two large randomized controlled trials BLISS52 and BLISS 76 [129]

References

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[2] F A Bonilla and H C Oettgen ldquoAdaptive immunityrdquo Journalof Allergy and Clinical Immunology vol 125 supplement 2 ppS33ndashS40 2010

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[4] TW Lebien andT F Tedder ldquoB lymphocytes how they developand functionrdquo Blood vol 112 no 5 pp 1570ndash1580 2008

[5] Y H Wang and Y J Liu ldquoThe IL-17 cytokine family and theirrole in allergic inflammationrdquo Current Opinion in Immunologyvol 20 no 6 pp 697ndash702 2008

[6] D D Chaplin ldquoOverview of the immune responserdquo Journal ofAllergy and Clinical Immunology vol 125 supplement 2 pp S3ndashS23 2010

[7] D PHuston ldquoThe biology of the immune systemrdquo Journal of theAmerican Medical Association vol 278 no 22 pp 1804ndash18141997

[8] W N Khan ldquoB cell receptor and BAFF receptor signalingregulation of B cell homeostasisrdquo Journal of Immunology vol183 no 6 pp 3561ndash3567 2009

[9] T Kurosaki and M Hikida ldquoTyrosine kinases and their sub-strates in B lymphocytesrdquo Immunological Reviews vol 228 no1 pp 132ndash148 2009

[10] L Le Pottier V Devauchelle J Pers C Jamin and P YouinouldquoThemosaic of B-cell subsets (with special emphasis on primarySjogrenrsquos syndrome)rdquo Autoimmunity Reviews vol 6 no 3 pp149ndash154 2007

[11] A Palanichamy J Barnard B Zheng et al ldquoNovel humantransitional B cell populations revealed by B cell depletiontherapyrdquo Journal of Immunology vol 182 no 10 pp 5982ndash59932009

[12] B Schiemann J L Gommerman K Vora et al ldquoAn essentialrole for BAFF in the normal development of B cells througha BCMA-independent pathwayrdquo Science vol 293 no 5537 pp2111ndash2114 2001

[13] J B Chung R A Sater M L Fields J Erikson and J GMonroe ldquoCD23 defines two distinct subsets of immature Bcells which differ in their responses to T cell help signalsrdquoInternational Immunology vol 14 no 2 pp 157ndash166 2002

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[15] K Willenbrock B Jungnickel M Hansmann and R KuppersldquoHuman splenic marginal zone B cells lack expression ofactivation-induced cytidine deaminaserdquo European Journal ofImmunology vol 35 no 10 pp 3002ndash3007 2005

[16] K Reif E H Ekland L Ohl et al ldquoBalanced responsivenessto chemoattractants from adjacent zones determines B-cellpositionrdquo Nature vol 416 no 6876 pp 94ndash99 2002

[17] GCinamonMA ZachariahOM Lam FW Foss Jr and J GCyster ldquoFollicular shuttling of marginal zone B cells facilitatesantigen transportrdquo Nature Immunology vol 9 no 1 pp 54ndash622008

[18] C D C Allen and J G Cyster ldquoFollicular dendritic cellnetworks of primary follicles and germinal centers phenotypeand functionrdquo Seminars in Immunology vol 20 no 1 pp 14ndash252008

[19] S Pillai and A Cariappa ldquoThe follicular versus marginal zoneB lymphocyte cell fate decisionrdquo Nature Reviews Immunologyvol 9 no 11 pp 767ndash777 2009

[20] R J Bende F VanMaldegem andC JMVanNoesel ldquoChronicinflammatory disease lymphoid tissue neogenesis and extran-odal marginal zone B-cell lymphomasrdquoHaematologica vol 94no 8 pp 1109ndash1123 2009

[21] G T Hart X Wang K A Hogquist and S C JamesonldquoKruppel-like factor 2 (KLF2) regulates B-cell reactivity subsetdifferentiation and trafficking molecule expressionrdquo Proceed-ings of the National Academy of Sciences of the United States ofAmerica vol 108 no 2 pp 716ndash721 2011

[22] K L Hoek L E Gordy P L Collins et al ldquoFollicular B celltrafficking within the spleen actively restricts humoral immuneresponsesrdquo Immunity vol 33 no 2 pp 254ndash265 2010

[23] E J Goetzl W Wang C McGiffert M Huang and M HGraler ldquoSphingosine 1-phosphate and its G protein-coupledreceptors constitute a multifunctional immunoregulatory sys-temrdquo Journal of Cellular Biochemistry vol 92 no 6 pp 1104ndash1114 2004

[24] J H Wang Q Wu P Yang et al ldquoType i interferon-dependentCD86high marginal zone precursor b cells are potent T cellcostimulators in micerdquo Arthritis and Rheumatism vol 63 no4 pp 1054ndash1064 2011

[25] G Shi K Harrison G L Wilson C Moratz and J H KehrlldquoRGS13 regulates germinal center B lymphocytes responsive-ness to CXC chemokine ligand (CXCL)12 and CXCL13rdquo Journalof Immunology vol 169 no 5 pp 2507ndash2515 2002

[26] V Pascual Y Liu A Magalski O De Bouteiller J Banchereauand J D Capra ldquoAnalysis of somatic mutation in five B cellsubsets of human tonsilrdquo Journal of Experimental Medicine vol180 no 1 pp 329ndash339 1994

[27] M Odendahl A Jacobi A Hansen et al ldquoDisturbed peripheralB lymphocyte homeostasis in systemic lupus erythematosusrdquoJournal of Immunology vol 165 no 10 pp 5970ndash5979 2000

[28] J Lee S Kuchen R Fischer S Chang and P E LipskyldquoIdentification and characterization of a human CD5+ pre-naive B cell populationrdquo Journal of Immunology vol 182 no 7pp 4116ndash4126 2009

[29] G P Sims R Ettinger Y Shirota C H Yarboro G G Illei andP E Lipsky ldquoIdentification and characterization of circulatinghuman transitional B cellsrdquo Blood vol 105 no 11 pp 4390ndash4398 2005

[30] J O Bohnhorst M B Bjoslashrgan J E Thoen J B Natvig and KM Thompson ldquoBm1-Bm5 classification of peripheral blood Bcells reveals circulating germinal center founder cells in healthy


individuals and disturbance in the B cell subpopulations inpatients with primary Sjogrenrsquos syndromerdquo Journal of Immunol-ogy vol 167 no 7 pp 3610ndash3618 2001

[31] Y Harada M M Kawano N Huang et al ldquoIdentificationof early plasma cells in peripheral blood and their clinicalsignificancerdquo British Journal of Haematology vol 92 no 1 pp184ndash191 1996

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[33] Y K Parrish I Baez T Milford et al ldquoIL-7 dependencein human B lymphopoiesis increases during progression ofontogeny from cord blood to bone marrowrdquo Journal ofImmunology vol 182 no 7 pp 4255ndash4266 2009

[34] S Giliani L Mori G De Saint Basile et al ldquoInterleukin-7receptor 120572 (IL-7R120572) deficiency cellular and molecular basesAnalysis of clinical immunological and molecular features in16 novel patientsrdquo Immunological Reviews vol 203 pp 110ndash1262005

[35] A Yoshimura T Naka andM Kubo ldquoSOCS proteins cytokinesignalling and immune regulationrdquo Nature Reviews Immunol-ogy vol 7 no 6 pp 454ndash465 2007

[36] P Youinou T E Taher J Pers R A Mageed and YRenaudineau ldquoB lymphocyte cytokines and rheumatic autoim-mune diseaserdquo Arthritis and Rheumatism vol 60 no 7 pp1873ndash1880 2009

[37] D I Mitsias A G Tzioufas C Veiopoulou et al ldquoThe Th1Th2 cytokine balance changes with the progress of the im-munopathological lesion of Sjogrenrsquos syndromerdquo Clinical andExperimental Immunology vol 128 no 3 pp 562ndash568 2002

[38] P Szodoray PAlex J G BrunMCentola andR Jonsson ldquoCir-culating cytokines in primary Sjogrenrsquos syndrome determinedby a multiplex cytokine array systemrdquo Scandinavian Journal ofImmunology vol 59 no 6 pp 592ndash599 2004

[39] M Fuxa and M Busslinger ldquoReporter gene insertions reveala strictly B lymphoid-specific expression pattern of Pax5 insupport of its B cell identity functionrdquo Journal of Immunologyvol 178 no 12 pp 8222ndash8228 2007

[40] S Yurasov H Wardemann J Hammersen et al ldquoDefective Bcell tolerance checkpoints in systemic lupus erythematosusrdquoJournal of Experimental Medicine vol 201 no 5 pp 703ndash7112005

[41] GMeyersa Y S Nga JM Bannocka et al ldquoActivation-inducedcytidine deaminase (AID) is required for B-cell tolerance inhumansrdquo Proceedings of the National Academy of Sciences of theUnited States of America vol 108 no 28 pp 11554ndash11559 2011

[42] E T Luning Prak M Monestier and R A Eisenberg ldquoB cellreceptor editing in tolerance and autoimmunityrdquo Annals of theNew York Academy of Sciences vol 1217 no 1 pp 96ndash121 2011

[43] Y Bergman and H Cedar ldquoA stepwise epigenetic processcontrols immunoglobulin allelic exclusionrdquo Nature ReviewsImmunology vol 4 no 10 pp 753ndash761 2004

[44] R C Lindsley M Thomas B Srivastava and D AllmanldquoGeneration of peripheral B cells occurs via two spatially andtemporally distinct pathwaysrdquo Blood vol 109 no 6 pp 2521ndash2529 2007

[45] A Brauninger T Goossens K Rajewsky and R KuppersldquoRegulation of immunoglobulin light chain gene rearrange-ments during early B cell development in the humanrdquo EuropeanJournal of Immunology vol 31 no 12 pp 3631ndash3637 2001

[46] K D Klonowski L L Primiano and M Monestier ldquoAtypicalV(H)-D-J(H) rearrangements in newborn autoimmune MRLmicerdquo Journal of Immunology vol 162 no 3 pp 1566ndash15721999

[47] K D Klonowski and M Monestier ldquoHeavy chain revisionin MRL mice a potential mechanism for the development ofautoreactive B cell precursorsrdquo Journal of Immunology vol 165no 8 pp 4487ndash4493 2000

[48] E Derudder E J Cadera J C Vahl et al ldquoDevelopment ofimmunoglobulin 120582-chain-positive B cells but not editing ofimmunoglobulin 120581-chain depends on NF-120581B signalsrdquo NatureImmunology vol 10 no 6 pp 647ndash654 2009

[49] R J Benschop D Melamed D Nemazee and J C CambierldquoDistinct signal thresholds for the unique antigen receptor-linked gene expression programs in mature and immature Bcellsrdquo Journal of Experimental Medicine vol 190 no 6 pp 749ndash756 1999

[50] L Verkoczy B Duong P Skog et al ldquoBasal B cell receptor-directed phosphatidylinositol 3-kinase signaling turns offRAGsand promotes B cell-positive selectionrdquo Journal of Immunologyvol 178 no 10 pp 6332ndash6341 2007

[51] M J Shlomchik A Marshak-Rothstein and C B WolfowiczldquoThe role of clonal selection and somatic mutation in autoim-munityrdquo Nature vol 328 no 6133 pp 805ndash811 1987

[52] T Litzenburger H Bluthmann P Morales et al ldquoDevelopmentof myelin oligodendrocyte glycoprotein autoreactive transgenicB lymphocytes receptor editing in vivo after encounter of a self-antigen distinct from myelin oligodendrocyte glycoproteinrdquoJournal of Immunology vol 165 no 9 pp 5360ndash5366 2000

[53] T Litzenburger R Fassler J Bauer et al ldquoB lymphocytes pro-ducing demyelinating autoantibodies development and func-tion in gene-targeted transgenic micerdquo Journal of ExperimentalMedicine vol 188 no 1 pp 169ndash180 1998

[54] L Menard D Saadoun I Isnardi et al ldquoThe PTPN22 alleleencoding an R620W variant interferes with the removal ofdeveloping autoreactive B cells in humansrdquo Journal of ClinicalInvestigation vol 121 no 9 pp 3635ndash3644 2011

[55] M Inaoki S Sato B C Weintraub C C Goodnow and T FTedder ldquoCD19-regulated signaling thresholds control periph-eral tolerance and autoantibody production in B lymphocytesrdquoJournal of Experimental Medicine vol 186 no 11 pp 1923ndash19311997

[56] T Guerrier P Youinou J O Pers and C Jamin ldquoTLR9drives the development of transitional B cells towards themarginal zone pathway and promotes autoimmunityrdquo Journalof Autoimmunity vol 39 no 3 pp 173ndash179 2012

[57] J A LyonsM SanM PHapp andAH Cross ldquoB cells are crit-ical to induction of experimental allergic encephalomyelitis byprotein but not by a short encephalitogenic peptiderdquo EuropeanJournal of Immunology vol 29 no 11 pp 3432ndash3439 1999

[58] E Bettelli D Baeten A Jager R A Sobel and V K KuchrooldquoMyelin oligodendrocyte glycoprotein-specific T and B cellscooperate to induce a Devic-like disease in micerdquo Journal ofClinical Investigation vol 116 no 9 pp 2393ndash2402 2006

[59] G Krishnamoorthy H Lassmann H Wekerle and A HolzldquoSpontaneous opticospinal encephalomyelitis in a double-transgenic mouse model of autoimmune T cellB cell cooper-ationrdquo Journal of Clinical Investigation vol 116 no 9 pp 2385ndash2392 2006

[60] N L Monson P Cravens R Hussain et al ldquoRituximabtherapy reduces organ-specific T cell responses and ameliorates


experimental autoimmune encephalomyelitisrdquo PLoS ONE vol6 no 2 Article ID e17103 2011

[61] O T Chan L G Hannum A M Haberman M P Madaioand M J Shlomchik ldquoA novel mouse with B cells but lackingserumantibody reveals an antibody-independent role for B cellsin murine lupusrdquo Journal of Experimental Medicine vol 189 no10 pp 1639ndash1648 1999

[62] F S Wong L Wen M Tang et al ldquoInvestigation of the role ofB-cells in type 1 diabetes in the NOD mouserdquo Diabetes vol 53no 10 pp 2581ndash2587 2004

[63] G Tchernev and C E Orfanos ldquoAntigen mimicry epitopespreading and the pathogenesis of pemphigusrdquo Tissue Antigensvol 68 no 4 pp 280ndash286 2006

[64] J Sokolove R Bromberg K D Deane et al ldquoAutoantibodyepitope spreading in the pre-clinical phase predicts progressionto rheumatoid arthritisrdquo PLoS One vol 7 Article ID e352962012

[65] B LMcRae C L VanderlugtM C Dal Canto and S DMillerldquoFunctional evidence for epitope spreading in the relapsingpathology of experimental autoimmune encephalomyelitisrdquoJournal of ExperimentalMedicine vol 182 no 1 pp 75ndash85 1995

[66] R Tisch X-D Yang SM Singer R S Liblau L Fugger andHOMcDevitt ldquoImmune response to glutamic acid decarboxylasecorrelateswith insulitis in non-obese diabeticmicerdquoNature vol366 no 6450 pp 72ndash75 1993

[67] A G Ziegler M Hummel M Schenker and E BonifacioldquoAutoantibody appearance and risk for development of child-hood diabetes in offspring of parents with type 1 diabetes the2-year analysis of the German BABYDIAB StudyrdquoDiabetes vol48 no 3 pp 460ndash468 1999

[68] D van der Woude S Rantapaa-Dahlqvist A Ioan-Facsinay etal ldquoEpitope spreading of the anti-citrullinated protein antibodyresponse occurs before disease onset and is associated withthe disease course of early arthritisrdquo Annals of the RheumaticDiseases vol 69 no 8 pp 1554ndash1561 2010

[69] M R Arbuckle M T McClain M V Rubertone et al ldquoDevel-opment of autoantibodies before the clinical onset of systemiclupus erythematosusrdquo New England Journal of Medicine vol349 no 16 pp 1526ndash1533 2003

[70] P Schneider F Mackay V Steiner et al ldquoBAFF a novel ligandof the tumor necrosis factor family stimulates B cell growthrdquoJournal of Experimental Medicine vol 189 no 11 pp 1747ndash17561999

[71] F Mackay and J L Browning ldquoBAFF a fundamental survivalfactor for B cellsrdquo Nature Reviews Immunology vol 2 no 7 pp465ndash475 2002

[72] FMackay S AWoodcock P Lawton et al ldquoMice transgenic forBAFF develop lymphocytic disorders along with autoimmunemanifestationsrdquo Journal of Experimental Medicine vol 190 no11 pp 1697ndash1710 1999

[73] R Brink ldquoRegulation of B cell self-tolerance by BAFFrdquo Seminarsin Immunology vol 18 no 5 pp 276ndash283 2006


[75] R Lesley Y Xu S L Kalled et al ldquoReduced competitivenessof autoantigen-engaged B cells due to increased dependence onBAFFrdquo Immunity vol 20 no 4 pp 441ndash453 2004

[76] M Thien T G Phan S Gardam et al ldquoExcess BAFF rescuesself-reactive B cells from peripheral deletion and allows them to

enter forbidden follicular andmarginal zone nichesrdquo Immunityvol 20 no 6 pp 785ndash798 2004

[77] J R Groom C A Fletcher S N Walters et al ldquoBAFF andMyD88 signals promote a lupuslike disease independent of Tcellsrdquo Journal of Experimental Medicine vol 204 no 8 pp1959ndash1971 2007

[78] F Mackay J R Groom and S G Tangye ldquoAn important rolefor B-cell activation factor and B cells in the pathogenesis ofSjogrenrsquos syndromerdquo Current Opinion in Rheumatology vol 19no 5 pp 406ndash413 2007

[79] P Youinou C Jamin and P M Lydyard ldquoCD5 expression inhuman B-cell populationsrdquo Immunology Today vol 20 no 7pp 312ndash316 1999

[80] R Berland andH HWortis ldquoOrigins and functions of B-1 cellswith notes on the role of CD5rdquo Annual Review of Immunologyvol 20 pp 253ndash300 2002

[81] K Yanaba J D Bouaziz K M Haas J C Poe M Fujimotoand T F Tedder ldquoA regulatory B cell subset with a uniqueCD1dhiCD5+ phenotype controls T cell-dependent inflamma-tory responsesrdquo Immunity vol 28 no 5 pp 639ndash650 2008

[82] C Mauri D Gray N Mushtaq and M Londei ldquoPreventionof arthritis by interleukin 10-producing B cellsrdquo Journal ofExperimental Medicine vol 197 no 4 pp 489ndash501 2003

[83] S Garaud A Morva S Lemoine et al ldquoCD5 promotes IL-10production in chronic lymphocytic leukemia B cells throughSTAT3 and NFAT2 activationrdquo Journal of Immunology vol 186no 8 pp 4835ndash4844 2011

[84] Y Renaudineau S Hillion A Saraux R A Mageed and PYouinou ldquoAn alternative exon 1 of the CD5 gene regulates CD5expression in human B lymphocytesrdquo Blood vol 106 no 8 pp2781ndash2789 2005

[85] S Garaud C Le Dantec S Jousse-Joulin et al ldquoIL-6ModulatesCD5 expression in B cells frompatients with lupus by regulatingDNA methylationrdquo Journal of Immunology vol 182 no 9 pp5623ndash5632 2009

[86] S Hillion A Saraux P Youinou and C Jamin ldquoExpressionof RAGs in peripheral B cells outside Germinal Centers isassociated with the expression of CD5rdquo Journal of Immunologyvol 174 no 9 pp 5553ndash5561 2005

[87] S Hillion M Dueymes P Youinou and C Jamin ldquoIL-6contributes to the expression of RAGs in humanmature B cellsrdquoJournal of Immunology vol 179 no 10 pp 6790ndash6798 2007

[88] K L Hippen L E Tze and T W Behrens ldquoCD5 maintainstolerance in anergic B cellsrdquo Journal of Experimental Medicinevol 191 no 5 pp 883ndash889 2000

[89] J C Poe M Hasegawa and T F Tedder ldquoCD19 CD21 andCD22 multifaceted response regulators of B lymphocyte signaltransductionrdquo International Reviews of Immunology vol 20 no6 pp 739ndash762 2001

[90] N R Pritchard and K G C Smith ldquoB cell inhibitory receptorsand autoimmunityrdquo Immunology vol 108 no 3 pp 263ndash2732003

[91] J G Cyster and C C Goodnow ldquoTuning antigen receptorsignaling by CD22 integrating cues from antigens and themicroenvironmentrdquo Immunity vol 6 no 5 pp 509ndash517 1997

[92] T F Tedder J Tuscano S Sato and J H Kehrl ldquoCD22 A Blymphocyte-specific adhesion molecule that regulates antigenreceptor signalingrdquo Annual Review of Immunology vol 15 pp481ndash504 1997

[93] S Sato A S Miller M Inaoki et al ldquoCD22 is both a positiveand negative regulator of B lymphocyte antigen receptor signal


transduction altered signaling in CD22-deficient micerdquo Immu-nity vol 5 no 6 pp 551ndash562 1996

[94] L Nitschke ldquoThe role of CD22 and other inhibitory co-receptors in B-cell activationrdquo Current Opinion in Immunologyvol 17 no 3 pp 290ndash297 2005

[95] P Engel Y Nojima D Rothstein et al ldquoThe same epitope onCD22 of B lymphocytes mediates the adhesion of erythrocytesT and B lymphocytes neutrophils and monocytesrdquo Journal ofImmunology vol 150 no 11 pp 4719ndash4732 1993

[96] T F Tedder J C Poe and KMHaas ldquoCD22 amultifunctionalreceptor that regulates B lymphocyte survival and signal trans-ductionrdquo Advances in Immunology vol 88 pp 1ndash50 2005

[97] CM Grimaldi R Hicks and B Diamond ldquoB cell selection andsusceptibility to autoimmunityrdquo Journal of Immunology vol 174no 4 pp 1775ndash1781 2005

[98] J A Walker and K G C Smith ldquoCD22 an inhibitory enigmardquoImmunology vol 123 no 3 pp 314ndash325 2008

[99] L Jin P A McLean B G Neel and H H Wortis ldquoSialic acidbinding domains of CD22 are required for negative regulationof B cell receptor signalingrdquo Journal of Experimental Medicinevol 195 no 9 pp 1199ndash1205 2002

[100] T L OrsquoKeefe G T Williams S L Davies and M S NeubergerldquoHyperresponsive B cells in CD22-deficient micerdquo Science vol274 no 5288 pp 798ndash801 1996

[101] T Dorner J KaufmannW AWegener N Teoh DM Golden-berg and G R Burmester ldquoInitial clinical trial of epratuzumab(humanized anti-CD22 antibody) for immunotherapy of sys-temic lupus erythematosusrdquoArthritis Research andTherapy vol8 no 3 p R74 2006

[102] A M Jacobi D M Goldenberg F Hiepe A Radbruch G RBurmester and T Dorner ldquoDifferential effects of epratuzumabon peripheral blood B cells of patients with systemic lupuserythematosus versus normal controlsrdquoAnnals of the RheumaticDiseases vol 67 no 4 pp 450ndash457 2008

[103] S D Steinfeld L Tant G R Burmester et al ldquoEpratuzumab(humanised anti-CD22 antibody) in primary Sjogrenrsquos syn-drome an open-label phase III studyrdquo Arthritis Research andTherapy vol 8 no 4 p R129 2006

[104] A Mizoguchi E Mizoguchi H Takedatsu R S Blumberg andA K Bhan ldquoChronic intestinal inflammatory condition gener-ates IL-10-producing regulatory B cell subset characterized byCD1d upregulationrdquo Immunity vol 16 no 2 pp 219ndash230 2002

[105] S Fillatreau C H Sweenie M J McGeachy D Gray and S MAnderton ldquoB cells regulate autoimmunity by provision of IL-10rdquo Nature Immunology vol 3 no 10 pp 944ndash950 2002


[107] B Wei P Velazquez O Turovskaya et al ldquoMesenteric B cellscentrally inhibit CD4+ T cell colitis through interaction withregulatory T cell subsetsrdquo Proceedings of the National Academyof Sciences of the United States of America vol 102 no 6 pp2010ndash2015 2005

[108] T Tretter R K C Venigalla V Eckstein et al ldquoInduction ofCD4+ T-cell anergy and apoptosis by activated human B cellsrdquoBlood vol 112 no 12 pp 4555ndash4564 2008

[109] A Mizoguchi E Mizoguchi R N Smith F I Preffer and AK Bhan ldquoSuppressive role of B cells in chronic colitis of T cellreceptor 120572mutant micerdquo Journal of Experimental Medicine vol186 no 10 pp 1749ndash1756 1997

[110] J G Evans K A Chavez-Rueda A Eddaoudi et al ldquoNovelsuppressive function of transitional 2 B cells in experimentalarthritisrdquo Journal of Immunology vol 178 no 12 pp 7868ndash78782007

[111] P A Blair K A Chavez-Rueda J G Evans et al ldquoSelectivetargeting of B cells with agonistic anti-CD40 is an efficaciousstrategy for the generation of induced regulatory T2-like B cellsand for the suppression of lupus in MRLlpr micerdquo Journal ofImmunology vol 182 no 6 pp 3492ndash3502 2009

[112] P A Blair L Y Norena F Flores-Borja et al ldquoCD19+ CD24hi

CD38hi B cells exhibit regulatory capacity in healthy individualsbut are functionally impaired in systemic lupus erythematosuspatientsrdquo Immunity vol 32 no 1 pp 129ndash140 2010

[113] C Jamin AMorva S Lemoine C Daridon A R DeMendozaand P Youinou ldquoRegulatory B lymphocytes in humans apotential role in autoimmunityrdquo Arthritis and Rheumatism vol58 no 7 pp 1900ndash1906 2008

[114] M Duddy M Niino F Adatia et al ldquoDistinct effector cytokineprofiles of memory and naive human B cell subsets andimplication in multiple sclerosisrdquo Journal of Immunology vol178 no 10 pp 6092ndash6099 2007

[115] J Correale M Farez and G Razzitte ldquoHelminth infectionsassociated with multiple sclerosis induce regulatory B cellsrdquoAnnals of Neurology vol 64 no 2 pp 187ndash199 2008

[116] C Mauri ldquoRegulation of immunity and autoimmunity by Bcellsrdquo Current Opinion in Immunology vol 22 no 6 pp 761ndash767 2010

[117] S Lemoine A Morva P Youinou and C Jamin ldquoHuman Tcells induce their own regulation through activation of B cellsrdquoJournal of Autoimmunity vol 36 no 3-4 pp 228ndash238 2011

[118] A Morva S Lemoine A Achour J Pers P Youinou and CJamin ldquoMaturation and function of human dendritic cells areregulated by B lymphocytesrdquo Blood vol 119 no 1 pp 106ndash1142012

[119] S Lemoine A Morva P Youinou and C Jamin ldquoRegulatory Bcells in autoimmune diseases how do they workrdquo Annals of theNew York Academy of Sciences vol 1173 pp 260ndash267 2009

[120] D A Einfeld J P Brown M A Valentine E A Clarkand J A Ledbetter ldquoMolecular cloning of the human B cellCD20 receptor predicts a hydrophobic protein with multipletransmembrane domainsrdquo EMBO Journal vol 7 no 3 pp 711ndash717 1988

[121] M A Valentine K E Meier S Rossie and E A ClarkldquoPhosphorylation of the CD20 phosphoprotein in resting Blymphocytes Regulation by protein kinase Crdquo Journal of Bio-logical Chemistry vol 264 no 19 pp 11282ndash11287 1989

[122] K C Anderson M P Bates and B L Slaughenhoupt ldquoExpres-sion of human B cell-associated antigens on leukemias andlymphomas amodel of humanB cell differentiationrdquoBlood vol63 no 6 pp 1424ndash1433 1984

[123] J HAnolik J Barnard A Cappione et al ldquoRituximab improvesperipheral B cell abnormalities in human systemic lupus erythe-matosusrdquo Arthritis and Rheumatism vol 50 no 11 pp 3580ndash3590 2004

[124] M J Leandro J C Edwards G Cambridge M R Ehrensteinand D A Isenberg ldquoAn open study of B lymphocyte depletionin systemic lupus erythematosusrdquo Arthritis and Rheumatismvol 46 no 10 pp 2673ndash2677 2002

[125] M Ramos-Casals M J Soto M J Cuadrado and M AKhamashta ldquoRituximab in systemic lupus erythematosus Asystematic review of off-label use in 188 casesrdquo Lupus vol 18no 9 pp 767ndash776 2009


[126] J Merrill J Buyon R Furie et al ldquoAssessment of flares inlupus patients enrolled in a phase IIIII study of rituximab(EXPLORER)rdquo Lupus vol 20 no 7 pp 709ndash716 2011

[127] B H Rovin R Furie K Latinis et al ldquoEfficacy and safety of rit-uximab in patients with active proliferative lupus nephritis theLupus Nephritis Assessment with Rituximab studyrdquo Arthritis ampRheumatism vol 64 no 4 pp 1215ndash1226 2012

[128] C Daridon D Blassfeld K Reiter et al ldquoEpratuzumab tar-geting of CD22 affects adhesion molecule expression andmigration of B-cells in systemic lupus erythematosusrdquo ArthritisResearch andTherapy vol 12 no 6 p R204 2010

[129] S V Navarra R M Guzman A E Gallacher et al ldquoEfficacyand safety of belimumab in patients with active systemiclupus erythematosus a randomised placebo-controlled phase3 trialrdquoThe Lancet vol 377 no 9767 pp 721ndash731 2011

Submit your manuscripts athttpwwwhindawicom

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


MEDIATORSINFLAMMATION

of


Behavioural Neurology

EndocrinologyInternational Journal of



Disease Markers


BioMed Research International

OncologyJournal of



Oxidative Medicine and Cellular Longevity


PPAR Research

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Immunology ResearchHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

ObesityJournal of



Computational and Mathematical Methods in Medicine

OphthalmologyJournal of


Diabetes ResearchJournal of



Research and TreatmentAIDS


Gastroenterology Research and Practice


Parkinsonrsquos Disease

Evidence-Based Complementary and Alternative Medicine

Volume 2014Hindawi Publishing Corporationhttpwwwhindawicom


Table 1 Characteristics of primary B cell subsets and their progenitors

Differentiation Subset Surface phenotypeProgenitor subsets (bone marrow) Pro-B B220loCD43+

AA41+Pre-B B220loCD43minus AA41+preBcR+Immature (23minus) B220lo sIgM+ sIgDminus CD23minusImmature (23+) CD19+ B220+ sIgM+ sIgDminus CD23+

Transitional subsets (spleen) T1 IgMhiCD23minus B220intAA41+T2 IgMhiCD23+ B220+AA41+T3 IgMloCD23+ B220+AA41+

Mature primary subsets Follicular zone IgMloCD23+ B220hiAA41minusMarginal zone CD19+IgMhiIgDlo CD23+ CD21+B1 CD43+ CD23minus CD5+

T-independent responses Early antibody-forming cellsshort-lived plasma cells B220loCD19+slg+iclghiT-dependent responses Early antibody-forming cellsshort-lived plasma cells B220loCD19+slg+iclghi

Germinal center B220+CD19+GL7+Long-lived plasma cells B220loslgminusiclg+Memory B220+slg+IgDminus

Natural antibodies Peritoneal B1a and B1b CD43+ CD23minus CD5+

through several distinct developmental stages During thisthey acquire their antigen specificity follow a program of dif-ferential surface antigen expression and sequential heavy andlight chain gene rearrangement forming the BCR (initiallyIgM) that determines the cell maturation stage Reachingthe immature stage B cells exit the BM and complete theirdevelopment to the mature or naıve stage which is signaledby the appearance of IgD in addition to IgM on the cellsurface This development sequence occurs in the absenceof any contact with exogenous antigen a stage known asantigen-independent B cell development [2ndash5]

22 B Cell Receptor Development Immunoglobulin mol-ecules are composed of 2 identical 50 kd heavy chainsand 2 identical 25 kd light chains [6] The genes encodingimmunoglobulins are assembled from segments in a mannerthat is entirely analogous to the process of T cell receptorgenes The light and heavy chain loci are each composed ofa series of V (variable) gene elements followed by severalD (diversity) segments (for the heavy chain gene only)some J (joining) segments and C (constant region) exonsHeavy chains (H) are assembled from 4 segments (VHD JH and CH) Light chains (L) are assembled from 3segments (VL JL andCL) (Figure 1)The genes for 9 differentheavy chain types (IgM IgD IgG1ndash4 IgA1-2 and IgE) arelocated on chromosome 14 and those for 2 light chaintypes (120581 or 120582) are on chromosome 2 and 22 respectivelyThe variable portions (V) of the H and L chains are injuxtaposition and this creates the antigen-binding portionof the immunoglobulin molecule These V regions contain3 highly variable subregions or hypervariable sequenceswhich produce the antigen-binding domain of the moleculeThe amino-terminal portions of the chains vary in aminoacid sequence from one antibody molecule to another Thecarboxyl terminal portions are constant in each subclass ofantibody The H chain constant regions form the Fc domain

of the molecule and are responsible for most of the effectorfunctions of the immunoglobulin molecule

The development process of different subsets of B cells hasbeen extensively reviewed elsewhere [4ndash7] and summarizedin Figure 1 Once a functional IgM and IgD are synthesizedthe pre-B cell evolves into an immature B cell The fullymature BCR includes additional transmembrane proteinsdesignated as Ig120572 and Ig120573 that activate intracellular signalsafter receptor binding to antigen [8 9] At that point thematureB cell passes to peripheral lymphoid tissues (Figure 2)

23 B Cell Classification according to Their Ontogenic StateAs soon as B cells have productively rearranged theirimmunoglobulin genes pro-B cells proceed to the pre-B cellstage On their arrival in the spleen immature B cells give riseto type-1 (BT1) type-2 (BT2) and possibly type-3 transitionalB cells [11] As transitional B cells they are pushed intomigrating from the BM to secondary lymphoid organs (SLO)Although T1 cells undergo apoptosis in response to BCRengagement they require signaling via the B cell activatingfactor belonging to the tumor necrosis factor (TNF) familyreceptor (BAFF-R TNFRSF13) to mature to the T2 stage[12] T2 cells are only present in the spleen and reside in thefollicles whereas T1 cells are found in the red pulp and outerperiarterial lymphatic sheath (PALS) [13]

There they continue maturing and are furtherselected by antigens As BT1 they present asCD20+CD5+CD10+minusCD21+minusCD23+minusIgM+IgD+minus andCD38+ but once they have evolved to type 2 (BT2) theybecome CD20+CD5+minusCD21++CD23+minusIgM++IgD++ andCD38+minus T2 B cells differentiate into either circulatinglymphocytes that get organized as germinal centers (GCs)or noncirculating lymphocytes that populate the marginalzone (MZ) Progression of T2 B cells towards MZ or GCsmay be determined by the quality of BCR-evoked signalsand the subsequent expression of the Notch proteins [14]


V V D D J J C C

Heavy chain gene

Heavy chain

V V J J C

Light chain gene

Light chain

COOH

COOHTMCIT


NH2

NH2 VL CLJL


















Plasma cell

MZ

Clonalexpansion

Clonalexpansion

Mem

LN

LN

Spleen

Lymphnode

Germinalcenter


Mat

MZ

PreBCR IgM

TdTRAG1RAG2


IgM + IgD


Germinalcenter

MZ B cell

High BCRsignal

Low BCRsignal

Sphingosine IP

BCA-1


T1 T2







BB

FDC

ShuttlingpDC

S1P in MZ

Marginal zone



B cell selectionCD4

DC69+DC86+Ag+

IFN120572 IL17

RgsCXCR5+

CXCR5+CXCL13

TH17


Plasma cell

Plasma cell

Bm2

Mantle zone

Dark zone

Bm3

Bm4

Bm4

Bm5Bm4

T-cell zoneBm1

Follicle

Bm2998400


























Bone marrow Spleen



Centralcheckpoint














BAFF APRIL






BAFF

Plasma cell

ImmatureB-Cell

migM


IgM

Plasma cell

Fo B cell

MZ B cell


GC75 self-reactive

15 self-reactive

BR3TACI

BCMA


35 self-reactive






























References
















































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















V V D D J J C C

Heavy chain gene

Heavy chain

V V J J C

Light chain gene

Light chain

COOH

COOHTMCIT


NH2

NH2 VL CLJL


















Plasma cell

MZ

Clonalexpansion

Clonalexpansion

Mem

LN

LN

Spleen

Lymphnode

Germinalcenter


Mat

MZ

PreBCR IgM

TdTRAG1RAG2


IgM + IgD


Germinalcenter

MZ B cell

High BCRsignal

Low BCRsignal

Sphingosine IP

BCA-1


T1 T2







BB

FDC

ShuttlingpDC

S1P in MZ

Marginal zone



B cell selectionCD4

DC69+DC86+Ag+

IFN120572 IL17

RgsCXCR5+

CXCR5+CXCL13

TH17


Plasma cell

Plasma cell

Bm2

Mantle zone

Dark zone

Bm3

Bm4

Bm4

Bm5Bm4

T-cell zoneBm1

Follicle

Bm2998400


























Bone marrow Spleen



Centralcheckpoint














BAFF APRIL






BAFF

Plasma cell

ImmatureB-Cell

migM


IgM

Plasma cell

Fo B cell

MZ B cell


GC75 self-reactive

15 self-reactive

BR3TACI

BCMA


35 self-reactive






























References
















































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of



















Plasma cell

MZ

Clonalexpansion

Clonalexpansion

Mem

LN

LN

Spleen

Lymphnode

Germinalcenter


Mat

MZ

PreBCR IgM

TdTRAG1RAG2


IgM + IgD


Germinalcenter

MZ B cell

High BCRsignal

Low BCRsignal

Sphingosine IP

BCA-1


T1 T2







BB

FDC

ShuttlingpDC

S1P in MZ

Marginal zone



B cell selectionCD4

DC69+DC86+Ag+

IFN120572 IL17

RgsCXCR5+

CXCR5+CXCL13

TH17


Plasma cell

Plasma cell

Bm2

Mantle zone

Dark zone

Bm3

Bm4

Bm4

Bm5Bm4

T-cell zoneBm1

Follicle

Bm2998400


























Bone marrow Spleen



Centralcheckpoint














BAFF APRIL






BAFF

Plasma cell

ImmatureB-Cell

migM


IgM

Plasma cell

Fo B cell

MZ B cell


GC75 self-reactive

15 self-reactive

BR3TACI

BCMA


35 self-reactive






























References
















































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















BB

FDC

ShuttlingpDC

S1P in MZ

Marginal zone



B cell selectionCD4

DC69+DC86+Ag+

IFN120572 IL17

RgsCXCR5+

CXCR5+CXCL13

TH17


Plasma cell

Plasma cell

Bm2

Mantle zone

Dark zone

Bm3

Bm4

Bm4

Bm5Bm4

T-cell zoneBm1

Follicle

Bm2998400


























Bone marrow Spleen



Centralcheckpoint














BAFF APRIL






BAFF

Plasma cell

ImmatureB-Cell

migM


IgM

Plasma cell

Fo B cell

MZ B cell


GC75 self-reactive

15 self-reactive

BR3TACI

BCMA


35 self-reactive






























References
















































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of




































Bone marrow Spleen



Centralcheckpoint














BAFF APRIL






BAFF

Plasma cell

ImmatureB-Cell

migM


IgM

Plasma cell

Fo B cell

MZ B cell


GC75 self-reactive

15 self-reactive

BR3TACI

BCMA


35 self-reactive






























References
















































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of



















BAFF APRIL






BAFF

Plasma cell

ImmatureB-Cell

migM


IgM

Plasma cell

Fo B cell

MZ B cell


GC75 self-reactive

15 self-reactive

BR3TACI

BCMA


35 self-reactive






























References
















































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















BAFF

Plasma cell

ImmatureB-Cell

migM


IgM

Plasma cell

Fo B cell

MZ B cell


GC75 self-reactive

15 self-reactive

BR3TACI

BCMA


35 self-reactive






























References
















































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of







































References
















































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
















Review Article B Lymphocytes: Development, Tolerance, and...

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