Direct and Indirect Mechanisms Cytokine Production by Mast Cells ...
Understanding the mechanisms by which B cells escape self ...315426/FULLTEXT01.pdf · Understanding...
Transcript of Understanding the mechanisms by which B cells escape self ...315426/FULLTEXT01.pdf · Understanding...
Understanding the mechanisms by whichB cells escape self tolerance
The role of CD35 and CD21 in the pathogenesis ofcollagen-induced arthritis
David Fernando Plaza
Degree project in biology, Master of science (2 years), 2010Examensarbete i biologi 45 hp till masterexamen, 2010Biology Education Centre and Department of Cell and Molecular Biology, Uppsala UniversitySupervisor: Sandra Kleinau
1
Contents
Abbreviations Abstract
1. Introduction 1.1. Pathogenesis of rheumatoid arthritis 1.2. Collagen induced arthritis 1.3. The complement system
1.3.1. Complement receptors 1.3.2. Complement receptors in autoimmunity
1.4. Marginal zone B cells 2. Materials and Methods
2.1. Hybridoma cell culture 2.2. Mice 2.3. Induction of CIA 2.4. In vivo CR1 blocking experiment 2.5. Anti‐BCII ELISA 2.6. Magnetic cell separation (MACS) of spleen B cells 2.7. B cell transfer into cr2+/+ and cr2‐/‐ mice 2.8. FACS 2.9. Statistics
3. Results 3.1. Increased CD19 expression in cr2‐/‐ mice on DBA/1 background. 3.2. CIA incidence after anti‐CR1 treatment. 3.3. CIA incidence in DBA/1 mice transferred with cr2‐/‐ B cells 3.4. Homing of cr2‐/‐ B cell in transferred DBA/1 mice 3.5. CIA incidence in cr2‐/‐ mice transferred with cr2+/+ B cells
4. Discussion 5. Acknowledgements 6. References
2
Abbreviations
Ab Antibody BCII Bovine collagen type II BSA Bovine serum albumin CIA Collagen induced arthritis CFA Complete Freund´s Adjuvant CR1 Complement receptor 1 CR2 Complement receptor 2 EDTA Ethylenediaminetetraacetic acid ELISA Enzyme linked immunosorbent assay FACS Fluorescence activated cell sorting FCS Fetal calf serum FDC Follicular dendritic cells FITC Fluorescein isothiocyanate i.d. Intradermal Ig Immunoglobulin IL Interleukin i.v. Intravenously mAb Monoclonal antibody MACS Magnetic activated cell sorting MHC Major histocompatibility complex MZ Marginal zone OD405 Optical density measured at 405 nm Ova Ovalbumin PBS Phosphate buffer saline PE Phycoerythrin RA Rheumatoid arthritis RCA Regulators of complement activation SD Standard deviation SLE Systemic lupus erythematous Th17 T helper 17 TNF‐α Tumor necrosis factor α WT Wild type
3
Abstract The immune response evoked in collagen induced arthritis (CIA) is dependent on the production of auto antibodies by B cells; however some other roles have been attributed to this cell population such as antigen presentation to T cells, cytokine secretion, expression of co stimulatory molecules and production of neolymphogenic compounds. To indirectly evaluate the effect of CD35/CD21 absence on B cell receptor signaling threshold, the expression level of CD19 was evaluated in DBA/1 mice deficient in CD35/CD21 (cr2‐/‐) and cr2+/+ DBA/1 mice. We found that leukocytes deficient in CD35/CD21 show increased expression of CD19 (10‐30% increase) in the DBA/1 genetic background. Adoptive transfer experiments were carried out to monitor the effect on CIA incidence and anti‐bovine collagen type (BCII) antibody production derived from transferring cr2‐/‐ and cr2+/+ B cells into cr2+/+ and cr2‐/‐ mice, respectively. The transfer of cr2‐/‐ B cells augments the risk of CIA in DBA/1 female mice. The relative amount of anti‐BCII IgG is higher in these animals 69 days post immunization. On the other hand, the transfer of cr2+/+ B cells reduces the risk of CIA in cr2‐/‐ female mice. The production of anti‐BCII IgM is lower in the animals transferred with cr2+/+ B cells 31 days post immunization. This experimental evidence suggests a strong association between the lacking of CD35 and CD21 and an increased risk of CIA, implying an important role of CD35/CD21 in tolerance breakage preceding CIA onset.
4
1. Introduction
1.1. Pathogenesis of rheumatoid arthritis
Rheumatoid arthritis (RA) is a chronic disease primarily affecting the joints, causing synovium inflammation, as well as cartilage and bone degradation mainly by the effector activity of matrix metallophylic macrophages (1). It is a complex autoimmune disease and its prognostic depends on many already established factors, such as genetic predisposition (2), gender bias and age (3). The reported incidence and prevalence of this inflammatory disease vary according to genetic background and age distribution of the population, as well as to diagnosis accuracy (4). Reliable incidence measurements are only available for Europe and North America, with 29 and 38 cases per 100,000 population, respectively (5). Different cytokines and lymphocyte populations have been shown to be involved in RA pathogenesis (6). Thus, the neutrophil recruiting role of T helper 17 (Th17) cells, a T cell subpopulation specialized on producing IL‐17, has been recently highlighted in RA pathophysiology (7,8). Th17 cells promote angiogenesis by inducing the production of proinflammatory cytokines, such as IL‐1 and TNF‐α, as well as it stimulates bone resorption, metalloproteinases activity and matrix catabolism (9,10). B cells have been seen to be involved in the pathogenesis of RA. Auto‐antibodies against citrullinated peptides or to the IgG Fc region (rheumatoid factor) are produced in RA patients (11), however, rheumatoid factor is also detected in the serum of 5% of the healthy population although at much lower titers. Rituximab, a B cell depleting therapy based on the specific recognition of the surface marker CD20, has been shown to significantly reduce the symptoms in RA patients (12). Apart from the established role on auto‐antibody production, B cells may perform various functions contributing to RA immune responses, such as cytokine production (both regulatory and activatory cytokines) and T cell activation, via antigen presentation and expression of co stimulatory molecules (12).
1.2. Collagen‐induced arthritis
The collagen‐induced arthritis (CIA) (13) model is induced by a single intradermal (i.d.) injection of collagen type II (CII) in complete Freund’s adjuvant (CFA) in the susceptible mouse strain DBA/1 (carrying the H‐2q MHC haplotype) (14). When using a dose of 50 µg CII per mouse a 90% and a 65% incidence of arthritis is observed in male and female DBA/1 mice respectively (15), however, using a lower CII dose of 20 µg reduces de incidence, particularly in female DBA/1 mice, in which only 20‐30% will develop a mild disease (16). The strong MHC haplotype correlation in mice and humans with arthritis indicates that the immune response in CIA and RA is highly dependent on T cell costimulation (17). The triggered immune response against CII evokes the production of IgM and IgG anti‐CII antibodies and promotes the development of polyarthritis (figure 1), with synovial infiltration and cartilage and bone destruction.
5
Figure 1. CIA model. DBA/1 female mice were injected i.d. with 20 µg of BCII in CFA and were monitored for scoring of joint inflammation from day 21 after immunization and onwards. Front and back unilateral swelling of limbs are shown.
1.3. The complement system
The complement system was discovered more than 100 years ago by Jules Bordet as a complement to the opsonizing and bactericidal activity of the immunoglobulins (18). This system comprises more than 30 serum proteins and receptors (19,20) that can be involved in a variety of functions, such as activation, regulation, antigen opsonization, assembly of pore forming complexes and chemotaxis. The system is divided into three different activation pathways: Classical, alternative and lectin; all of them leading to the proteolytic cleavage and activation of the central components C3 and C5 (figure 2).
Figure 2. The complement system. Classical, lectin and alternative complement pathways. As a consequence of complement system activation, C3 degradation products are formed, able to bind to complement receptors on immune cells. Adapted from (21).
The classical pathway was the first activation route to be discovered. This is based on the immune complex recognition by C1q. C1q is a homohexamer composed by filamentous subunits, having a globular domain and a collagen like region at each of the ends. The binding of C1q to the Fc part of the antibody in an immune complex leads to the activation of the serine protease heterodimer C1r/C1s. C1r/C1s cleaves C4 and C2, forming together the classical pathway C3 convertase (22).
6
Some sugars on pathogen surfaces are recognized by two different lectins, mannose binding lectin (23) and ficolin. These two lectins have a structure resembling C1q and form a complex with the C1r/C1s‐like serine proteases MASP1 and MASP2. Once the whole complex is activated, it cleaves C4 and C2, assembling the same C3 convertase that is used by the classical activation pathway (24). The alternative pathway is mainly considered an amplification route for the other two activation pathways. The pathway is triggered by the spontaneous cleavage of the C3 molecule into C3b and C3a in a process called C3 tickover. Afterwards, more C3 molecules are proteolytically cleaved by the alternative pathway C3 convertase (C3bBb) and the reaction is amplified (25). C3b stays attached to the antigen surface and binds to the already formed alternative or classical/lectin pathways C3 convertases (C3Bb or C4b2b) to generate the C5 convertase. This will cleave C5 into C5b and C5a, where C5b acts as a binding substrate for the components of the membrane attack complex, C6, C7, C8 and C9. The membrane attack complex forms a pore shaped structure that osmotically lyses a reduced group of thin wall gram‐negative bacteria such as species of the genus Neisseria (26,27). The small fragments produced from the C3 and C5 cleavage, C3a and C5a, work as chemoattractants able to recruit a variety of immune cells. The accumulation of immune complexes in joints leads to excessive proteolysis of C3 and C5 that promotes the anaphylatoxins C3a and C5a, which recruit neutrophils and macrophages into the joint synovium (23). 1.3.1. Complement receptors
There are several complement receptors (28) and two of them, CR1 (CD35) and CR2 (CD21), have shown to be important in the regulation of the adaptive immune response. In mouse, these receptors are produced by alternative splicing from the cr2 gene primary transcript, giving rise to the expression of a short product (CR2) and a long one (CR1). The basic structure of both receptors is highly similar (figure 3), including short consensus repeats composed of 60 amino acids (29). CD35 and CD21 are widely expressed on a variety of immune cells subpopulations in human, such as T cells, B cells, macrophages, FDC and erythrocytes. On the other hand, the expression of these receptors is restricted to B cells and FDC in mice (30). CD35 mediates phagocytosis of immune complexes bound to C3 degradation fragments, while CD21 binds simultaneously with BCR to immune complexes containing iC3b and C3d, promoting B cell activation and proliferation.
7
Figure 3. Mouse complement receptors 1 (CD35) and 2 (CD21). CD35 and CD21 are alternative splice products from the gene cr2. The different C3 proteolysis products acting as ligands are shown, as well as the binding sites for two commonly used monoclonal antibodies employed for the characterization of these receptors, 8C12 and 7E9. Adapted from (29).
Recently, it has been shown that CR1 molecules expressed on the surface of MZ B cells, transport immune complex from the marginal zone to the spleen follicles, transferring high molecular weight antigens to the resident FDC. The same CR1‐mediated transport is responsible of transporting immune complexes involving high molecular weight antigens to the lymph node follicles (31). Inside the lymph nodes, naive B cells are responsible of transporting the C3‐coated immune complexes into the follicles (32,33). Studies in CD35/CD21 deficient mice, generated on a C57Bl/6 genetic background, have shown that these mice have increased CD19 expression (34), reduced amounts of CD5+ B1 cells (35) and decreased IgM and IgG titers towards sheep red blood cells (36). 1.3.2. Complement receptors in autoimmunity Contradictory results have been published regarding the role of CD35/CD21 in CIA. Recently, Kristine Kuhn and colleagues used male cr2‐/‐ DBA/1j mice and 400 µg of BCII in CFA to establish CIA. Their results demonstrated that deficiency in CD35/CD21 significantly reduces the CIA severity compared to wild type (WT) DBA/1 males and that the production of anti‐cyclic citrullinated peptide antibodies is reduced, as well as the level of anti‐BCII and anti‐murine CII IgG and IgG2a antibodies (37). In contrast, our group recently reported increased CIA incidence in cr2‐/‐ female DBA/1 mice injected with low BCII dose (20 µg/dose) in CFA compared to WT female DBA/1 mice (16). The cr2‐/‐ female DBA/1 mice demonstrated also increased complement levels and sustained IgM anti‐CII response compared to WT females. It has been shown that the expression of CD35 and CD21 is significantly reduced on peripheral B cells of patients with systemic lupus erythematosus (SLE) (38,39). Or group has shown that the percentage of peripheral B cells expressing CD35 and CD21, as well as the expression level of these two receptors, are significantly reduced in RA patients (data not published). Issak and collaborators have shown that CD35 expression is profoundly reduced on memory B cells derived from SLE patients; however, this reduction can be a consequence of a negative feedback loop in the SLE immune response rather that a factor predisposing the individual to SLE development (40). Previous studies have shown that the presence of C3b (CD35 ligand) inhibits the proliferation of tonsil derived human B cells activated with anti‐IgM, IL‐2 and IL‐15 in vitro, remarking the inhibitory function of CD35 in human B cell activation (41). 1.4. Marginal zone B cells
The spleen is a complex secondary lymphoid organ responsible for the capture and processing of blood born antigens and the triggering of the immune response against them. It also removes the senescence erythrocytes from the circulation that are phagocytosed by the resident macrophages. The whole erythrocyte turn over process is carried out in the red pulp. The spleen is irrigated by an afferent artery branching into the white pulp and delivering its content into the marginal zone dividing the red pulp (erythrocyte turn over structure) from the white pulp (lymphoid structure) (figure 4) (42).
8
Figure 4. General architecture of the spleen. Two regions are clearly distinguishable: The red pulp constituted of cords and venous sinuses and the white pulp formed by lymphoid tissue. The lymphoid white pulp includes regions of antigen capture and processing; a T cell zone where the antigen is presented and B cell follicles where the B cells are activated and the affinity maturation takes place. Image adapted from (42).
The white pulp, following the common pattern shown by most secondary lymphoid organs, is composed by professional antigen presenting cells, macrophages, T cells and B cells, the latter either forming follicles or surrounding the whole structure in the form of marginal zone (MZ) B cells. Those MZ B cells are characterized by the expression of IgMhi, IgDlo, CD23‐, CD21hi and CD1dhi and produce high amounts of low affinity IgM and IgG (43). These cells have been shown to be important in the immune response against encapsulated bacteria and T independent multivalent antigens. Another important function of the MZ B cell population lies on the transport of immune complexes from the MZ to the B cell follicles as a constant antigen supplier to the stroma derived follicular dendritic ells (FDC), acting basically as an antigen “shuttle” (44). Aim The aim of this project is to evaluate the role of CD35 and CD21 on B cells in the pathogenesis of CIA, bearing in mind the reported importance of B cells in the immunopathogenesis of RA. To accomplish this, female cr2‐deficient DBA/1 mice (cr2‐/‐) and female WT DBA/1 mice were used in different CIA experiments, including in vivo blockage of CR1 and the adoptive transfer of cr2‐/‐ and cr2+/+ B cells into DBA/1 and cr2‐/‐ female mice.
9
2. Materials and Methods
2.1 Hybridoma cell culture The B cell hybridoma cell line, 8C12, a rat IgG2a monoclonal antibody to mouse CD35, was maintained in culture and constantly expanded in DMEM (SVA, Uppsala, Sweden) supplemented with 5% fetal calf serum (FCS), 10 mM HEPES, 2 mM L‐glutamine, 50 µM β‐mercaptoethanol and 1 µg/ml streptomycin/penicillin. Nine liters of culture supernatant were collected and filtered through a 0.45 µm pore diameter nitrocellulose membrane. A previously equilibrated 25 ml GammaBind Plus Sepharose column (Pharmacia Biotech, Uppsala, Sweden) was employed to purify the monoclonal antibodies produced. The column was washed with 125 ml NaH2PO4 * H2O and the bound antibodies were detached using a 100 mM glycine‐HCl solution (pH 2.7), collecting 16 x 2 ml fractions per liter of culture supernatant. The fractions were directly neutralized with 300 µl/fraction of 1 M Tris‐HCl (pH 8.5). The OD280 was measured to establish the fractions containing monoclonal antibodies. The fractions with an antibody concentration above 100 µg/ml were pooled and concentrated to 3 mg/ml utilizing Amicon Ultra‐15 Centrifugal Filter Units with Ultracel‐50 membrane (Millipore, Cork, Ireland) according to the manufacturer instructions. The concentration was calculated according to the formula: Concentration (mg/ml) = (OD280/1.5). 2.2 Mice DBA/1 and cr2‐deficient DBA/1 (cr2‐/‐) mice were used. The mice were used at 4‐6 weeks of age. The animals were kept at Uppsala Biomedical Centre Animal Facility and feed ad libitum with water and dry pellets. All experiments were approved by the local ethics committee (Uppsala tingsrätt, Sweden).
2.3 Induction of CIA Two mg/ml bovine CII (BCII) stock solution was prepared in 10 mM ascetic acid. The BCII stock solution was additionally diluted with PBS to 800 µg/ml and a 1:1 emulsion with complete Freund´s adjuvant (CFA) was prepared. The animals were anesthetized with isofluran (Baxter Healthcare, Kista, Sweden) and injected intradermally with 50 µl of the emulsion at the base of the tail giving 20 µg of BCII per mouse. After day 20 post immunization, arthritic scores were assessed every other day to establish CIA incidence, severity and onset day. The arthritic score was assigned according to the following observations: One point was given for each swelling finger, five points per swelling mid paw and five points per wrist or ankle, giving a maximum score of 15 per limb (60 per animal).
2.4 In vivo CR1 blocking experiment In order to evaluate the effect of CD35 blocking on CIA incidence, 300 µg of rat IgG2a anti‐mouse CD35 (clone 8C12) were intravenously (i.v.) injected into 9 DBA/1 female mice two days prior immunization with 20 µg BCII in CFA. As controls, 9 animals were injected with 300 µg of IgG2a anti‐OVA (clone O3G64) before collagen immunization, whereas 6 additional animals were immunized with the same collagen concentration without any previous treatment. The mice were bled on days 5, 11, 20 and 41 post immunization to perform IgM and IgG anti‐BCII ELISAs. Arthritic scores were assessed every other day, starting 20 days after immunization, to establish CIA incidence, severity and onset day.
10
2.5 Anti‐BCII ELISA
For IgM measurement, 96 well plates were coated with 10 µg/well BCII in PBS, and incubated for 72 h at 4°C in a humid chamber. Thereafter, the plates were washed using 0.05% Tween‐20 in PBS (washing buffer) and the remaining unspecific binding sites were blocked with 1% BSA in PBS (blocking buffer). The sera were diluted 1:20, 1:40, 1:80 and 1:160 and added in the wells by duplicate. Some independent wells were coated with blocking buffer to determine the background optical density and the plates were incubated overnight at room temperature in a humid chamber. The plates were then rinsed employing washing buffer and 1:500 polyclonal alkaline phosphatase‐conjugated rat anti‐mouse IgM (Sigma‐Aldrich, Steinheim, Germany) was added and incubated for 2 h at room temperature. After the plates were profusely washed, 50 µl of 1 mg/ml P‐nitrophenylphosphate in 1 M diethanolamine / 1 mM MgCl2 buffer were added. After 90 min of incubation at room temperature the OD405 was measured in a Versamax tunable microplate reader (Molecular Devices, Sunnyvale, CA). IgG anti‐BCII ELISA was performed as for IgM, but adapting a few steps. The plates were coated with 5 µg/well BCII and incubated overnight at 4°C in a humid chamber. Sera were diluted 1:100, 1:1000 and 1:10000 in duplicate and incubated for 2 h at room temperature. Polyclonal alkaline phosphatase‐conjugated sheep anti‐mouse IgG (1:7000 F(ab´)2 fragments) were used for IgG detection. The OD405 was measured after 40 min incubation at room temperature in the presence of alkaline phosphatase substrate.
2.6 Magnetic activated cell sorting (MACS) of B cells Wild type and cr2‐/‐ mice were killed by CO2 and the spleens were surgically removed. A homogeneous cell suspension was prepared by disaggregating the spleen on a sterile alum mesh over a petri dish with PBS. The cell suspensions were centrifuged at 300 x g for 7 min and the cells were suspended in 5 ml ACK lysing buffer (150 mM NH4Cl, 9 mM KHCO3 and 10 µM EDTA.Na2∙2H2O) for 5 min to lyse the erythrocytes. Thereafter, 5 ml of PBS (137 mM NaCl, 2.68 mM KCl, 8.09 mM Na2HPO4*2H2O and 1.47 mM KH2PO4) were added to stop the lysis reaction. The suspended cells were counted in a Bürker chamber and adjusted to 1.11 x 108 cells/ml in degassed 0.5 % BSA (Merck, Darmstadt, Germany) in PBS (MACS buffer). The cell suspension was stained with 250 ng/1 x 106 cells of biotin‐conjugated anti‐mouse CD43 (clone eBioR2/60, eBioscience, San Diego, CA) and incubated for 25 min at 4°C. Subsequently, the cells were spinned down and suspended in the same volume of MACS buffer used earlier to adjust the cell density up to 1.11 x 108 cells/ml. One µl/2 x 106 cells streptavidin‐conjugated magnetic beads (MiltenyiBiotec, San Diego, CA) was added and incubated for 25 min at 4°C. Finally, the cells were washed, resuspended in 500 µl MACS buffer and sorted through pre chilled LS columns (Miltenyi, Bergisch Galdbach, Germany). The CD43 negative fraction (B cells) was collected, washed and suspended in sterile PBS. The cells were counted and the cell density adjusted to 3.3 x 106 cells/ml.
2.7 B cell transfer into cr2+/+ and cr2‐/‐ mice Four to six weeks old cr2+/+ and cr2‐/‐ female DBA/1 mice were randomly distributed into 4 different groups; two groups of cr2+/+ mice and two groups of cr2‐/‐ mice. The two groups of each strain were then injected i.v. with 1‐1.5 million cr2‐/‐ B cells or cr2+/+ B cells suspended in 300 µl PBS. In addition, two control groups, each consisting of 12 cr2+/+ and 4 cr2‐/‐ female mice, were treated with PBS only (300 µl/mouse). The mice were bled on days 11, 31 and 69 post immunization for measuring antibody levels to BCII.
11
2.8 FACS
To evaluate the purity of the B cells injected into the recipients, as well as to establish the homing of the transferred B cells and to measure CD19 expression in cr2‐/‐ DBA/1 mice we performed FACS analyses. Mice that had been injected with B cells were killed at the end of the experiment (day 69 post immunization), the spleens were removed and splenocyte suspensions prepared. Samples of MACS separated B cells (to be transferred) and splenocytes from B cell transferred mice were suspended in 0.5% BSA in PBS (FACS buffer), counted and adjusted to 2 x 106 cells/ml. One hundred µl of cell suspension were added per FACS tube. To establish the purity of B cells, 5 x 105 cells from the MACS sorting were stained with Phycoerythrin (PE)‐conjugated anti‐mouse B220 (clone RA3‐6B2; BD Pharmingen, San Diego, CA) and Fluorescein isothiocyanate (FITC)‐conjugated anti‐mouse CD3 (clone DaA3; EuroBioSciences, Friesoythe, Germany). In order to examine the homing of the transferred B cells into the recipient mice, the splenocytes were stained with FITC‐conjugated anti‐mouse B220 (clone RA3‐6B2; BD Pharmingen, San Diego, CA) and biotin‐conjugated anti‐mouse CD35 (clone 8C12; BD Pharmingen, San Diego, CA) for 20 min at 4°C. Thereafter, the cells were washed and stained with PE‐conjugated streptavidin for 20 min at 4°C. Additional FACS tubes with cells were incubated with FITC and PE‐conjugated rat IgG2a (BD Pharmingen, San Diego, CA) and used as isotype controls. After staining, the cells were washed and suspended in 500 µl of 1% paraformaldehyde in PBS. To compare the expression of CD19 on leukocytes (B cells) isolated from DBA/1 and cr2‐/‐ mice, spleen and lymph nodes were extracted from 3 females and 3 males of each strain. Cells suspensions were prepared as described above from spleen and pooled lymph nodes from individual mouse and the cell concentration adjusted to 2 x 106 cells/ml. Two hundred thousand cells were stained with rat anti‐mouse PE‐conjugated CD19 (clone 1D3; BD Pharmingen, San Diego, CA) for 20 min at 4°C in the dark. As a control of unspecific antibody binding, similar number of cells was incubated with PE‐conjugated rat IgG2a for 20 min at 4°C in the dark. The unbound antibody was removed by washing and the cells were fixed using 500 µl of 1% paraformaldehyde in PBS. The samples were acquired on a FACScan (BD Biosciences, San Diego, CA) equipped with a 480 nm argon laser and analyzed using CellQuest software (BD Biosciences, San Diego, CA).
2.9 Statistics Statistical significance on IgM and IgG anti‐BCII levels among different groups was calculated using two tailed student T‐test. Student T‐test was also used to verify differences on CD19 expression level. Fisher exact test was utilized to evaluate the statistical significance on CIA‐incidence.
12
3. Results 3.1. Increased CD19 expression in cr2‐/‐ mice on DBA/1 background. It has previously been reported that CD19 expression is enhanced in cr2‐/‐ C57BI/6 mice (34). To verify that this is also the case when cr2 knock‐outs are on a DBA/1 background we analyzed CD19 in cr2‐/‐ DBA/1 mice in comparison with WT DBA/1 mice. We found that CD19 expression was significantly increased in male lymph nodes (p = 0.003, figure 5) and female spleens (data not shown, p = 0.0004). A tendency towards higher expression of this B cell marker was also observed in the spleen of males (figure 5).
Figure 5. Expression of CD19 in cr2‐/‐ DBA/1 mice. A. The average + standard deviation (SD) of the mean fluorescence intensity (MFI) of CD19 on splenocytes and lymph node cells from 3 DBA/1 male mice and 3 cr2‐deficient DBA/1 male mice are shown. B. Two representative overlaid histograms corresponding to splenocytes and lymph node cells from a DBA/1 and a cr2‐/‐ mouse. * = p < 0.05
3.2. CIA incidence following anti‐CR1 treatment. In order to evaluate the role of CR1 in CIA pathogenesis in DBA/1 mice, we blocked the amino terminal region of CR1 using the monoclonal antibody 8C12 in vivo. Control DBA/1 mice were treated i.v. with 300 µg anti‐Ova (O3G64) in PBS or left untreated. The mice were treated 24 h before immunization with BCII. We assessed the arthritic scores every second day beginning on day 21 post immunization to determine disease severity, time of onset and CIA incidence. No conspicuous effect on the incidence of the anti‐CR1 treated animals compared to the incidence of the anti‐Ova injected animals was found (figure 6), although, anti‐CR1 treated mice showed a tendency of increased arthritis incidence compared to the anti‐Ova treated mice. Notably, both anti‐CR1 and anti‐Ova treatments seemed to induce higher CIA incidence in mice than in untreated individuals.
13
Figure 6. CIA incidence in DBA/1 mice treated with anti‐mouse CR1. A trend is observed towards a higher incidence of CIA in anti‐CR1 injected group (n = 9) compared to the anti‐Ova (n = 9) and non‐injected groups (n = 6).
Regarding IgM anti‐BCII antibodies in the animals, we found that all groups produced similar levels of IgM at different time points after immunization (figure 7). The highest anti‐BCII levels were observed at day 20 post immunization, with animals treated with anti‐CR1 or anti‐Ova having somewhat stronger IgM response to BCII than untreated mice.
Figure 7. Relative concentration of IgM anti‐BCII in mice treated with anti‐CR1 antibodies. Similar amounts of IgM anti‐BCII were observed in BCII‐immunized animals treated with anti‐mouse CR1 monoclonal antibody (mAb) (clone 8C12) (n = 10), anti‐Ova mAb (clone O3G64) (n = 9) or left untreated (n = 6) at all time points evaluated. The values shown represent the mean + SD OD405 of sera. As positive controls, two sera from earlier BCII‐immunized animals were used. Serum from naïve DBA/1 was used as negative control.
3.3. CIA incidence in DBA/1 mice transferred with cr2‐/‐ B cells To elucidate the role of CD35 and CD21 in the regulation of B cells in CIA, DBA/1 mice were transferred i.v. with cr2+/+ B cells or cr2‐/‐ B cells. A separate control group was injected i.v. with PBS only. Three days after cell transfer or PBS the animals were immunized with BCII. An outstandingly high CIA incidence (63%) was observed from day 53 in animals receiving cr2‐/‐ B cells compared to the groups that were injected with cr2+/+ (33%) or PBS (25%) (figure 8). No significant differences on the mean day of onset were observed between the groups (cr2‐/‐ B cells: 42.71 ± 7.16; cr2+/+ B cells: 50.67
14
± 11.50; PBS: 50.80 ± 20.17). No difference in CIA severity was observed among the different groups of mice.
Figure 8. CIA incidence in DBA/1 mice transferred with cr2‐/‐ B cells. Female DBA/1 mice were injected i.v. with either cr2‐/‐ B cells (n = 12 mice), cr2+/+ B cells (n = 9 mice). No statistically significant differences between the treatments were found, but a clear trend is observed towards higher CIA incidence in the cr2‐/‐ B cell transferred group compared to the cr2+/+ B cell transferred or PBS injected groups.
IgM and IgG production against BCII was measured at different time points after immunization in the DBA/1 mice transferred with cr2+/+ or cr2‐/‐ B cells, or injected with PBS. No differences were found in the IgM production between the groups on days 11 and 31 after immunization. However, sixty nine days post immunization, the production of IgG was significantly higher in DBA/1 mice transferred with cr2‐/‐ B cells than in DBA/1 animals transferred with cr2+/+ (figure 9).
Figure 9. Antibody production against BCII in DBA/1 mice transferred with cr2‐/‐ B cells. The production of (A) IgM and (B) IgG anti‐BCII in serum of BCII‐immunized female DBA/1 mice injected i.v. with either cr2‐/‐ B cells (n = 12 mice), cr2+/+ B cells (n = 9 mice) or PBS (n = 12 mice). Significantly higher production of IgG was observed in animals transferred with cr2
‐/‐ B cells compared to those transferred with cr2
+/+ B cells at day 69 post
immunization. The values shown represent the mean OD405 + SD for sera. As positive control, serum from a previously BCII immunized animal was used. Serum from naïve DBA/1 was used as negative control. * = p < 0.05
15
3.4. Homing of cr2‐/‐ B cells in transferred DBA/1 mice
To evaluate the homing of cr2‐/‐ B cells in the spleen of recipient mice, we extracted and processed the spleens at the end of the adoptive transfer experiment. The expression of CR1 (CD35) and B220 of the splenocytes was investigated by FACS.
Table 1. cr2‐/‐ B cell homing in the spleen of DBA/1 mice transferred 73 days earlier. The table shows the development (Y) or not (N) of CIA in the individual DBA/1 mice (n = 5) injected i.v. with cr2‐/‐ B cells. The data demonstrates the amount of CD35 positive and CD35 negative B220+ B cells respectively in the spleen of the mice. Three out of five mice demonstrate cr2‐/‐ B cells in the spleen. There is no correlation between the homing of CD35 negative cells in the host spleens and the development of CIA at day 69 post immunization.
Sixty percent of the studied mice showed percentages of CD35‐ B cell higher than 25% in spleen, while 40% of them had a percentage of CD35‐ B cells higher than 95 % (table 1). Despite these high rates of long term CD35‐/B220+ cell homing in transferred DBA/1 female mice, we found no direct correlation between the percentage of CD35‐/B220+ cells in the spleen at day 69 post immunization and the development of CIA (table 1).
3.5. CIA incidence in cr2‐/‐ DBA/1 mice transferred with cr2+/+ B cells To evaluate whether the acquisition of B cells expressing CD35 and CD21 is able to protect cr2‐/‐ female DBA/1 mice from CIA development, cr2‐/‐ mice were transferred with cr2+/+ B cells, cr2‐/‐ B cells or injected with PBS only. Three days later, the mice were immunized with BCII in CFA. A prominent delay in the CIA onset was observed in the group transferred with cr2+/+ B cells compared to the control groups receiving cr2‐/‐ B cells or PBS (figure 10). Thus, the CIA incidence in the cr2+/+ B cell injected group was conspicuously lower (20%) than the incidences shown by the group injected with PBS (75%) and the group transferred with cr2‐/‐ B cells (60%) at the end of the experiment. No statistically significant differences in CIA onset day and severity were observed.
16
Figure 10. CIA incidence in cr2‐/‐ DBA/1 mice transferred with cr2+/+ B cells. Female cr2‐/‐ mice were injected i.v. with either cr2+/+ B cells (n = 5 mice), cr2‐/‐ B cells (n = 5 mice) or PBS (n = 4 mice). No statistically significant differences between the treatments were found, but a clear trend is observed towards a lower CIA incidence in the cr2+/+ B cell transferred group compared to the cr2‐/‐ B cell transferred or PBS injected groups.
IgM and IgG production against BCII was measured at different time points after immunization in the cr2‐/‐ DBA/1 mice transferred with cr2+/+ or cr2‐/‐ B cells, or injected with PBS. The animals that were subjected to cr2+/+ B cell transfer showed a significantly lower production of IgM than those animals that were transferred with cr2‐/‐ B cells at day 31 post immunization (figure 11).
Figure 11. Antibody production against BCII in cr2‐/‐ DBA/1 mice transferred with cr2+/+ B cells. The production of (A) IgM and (B) IgG anti‐BCII in serum of BCII‐immunized cr2‐/‐ female mice injected i.v. with either cr2+/+ B cells (n = 5 mice), cr2‐/‐ B cells (n = 5 mice) or PBS (n = 4 mice) was evaluated. Significantly lower production of IgM was observed in animals that were transferred with cr2+/+ B cells compared to those transferred with cr2‐/‐ B cells at day 31 post immunization. The values shown represent the mean OD405 + SD. As positive control, serum from a previously BCII‐immunized animal was used. Serum from naïve DBA/1 mice was used as negative control. * = p < 0.05
17
4. Discussion It is widely accepted that CR2 function lies on decreasing the activation thresholds of the B cell towards low concentration of immune complexes opsonized with C3d. By definition, this makes this complement receptor an activating input for the B cell. Bearing in mind that CR1 and CR2 share the carboxy‐terminal region responsible of triggering intracellular signal transduction pathways, one could predict that CR1 should present a similar stimulatory function; however, experiments carried out in our lab have shown that female cr2‐/‐ DBA/1 mice are around 70% more susceptible to CIA than WT DBA/1 animals (16). Furthermore, our previous study of CR1 and CR2 expression on CD19+ B cells in humans, demonstrated that the expression of these receptors is down regulated on peripheral blood B cells from RA patients (non published data), suggesting that CR1 and CR2 play a role in the autoimmune phenotype of those individuals. CD19, CD81, CD21 and CD35 are different BCR complex coreceptors (45). Mice lacking CR1/2 tend to overexpress CD19, and this phenomenon can be considered a compensatory measurement to maintain the B cell activation threshold near to WT levels and to promote B cell survival, which is directly dependant on the strength of the signal via BCR at different stages of B cell maturation and activation (28). We found an increased expression of CD19 (10%‐30%) on splenocytes and lymph node derived cells obtained from cr2‐/‐ DBA/1 females and males compared to their WT DBA/1 counterparts. This increased expression can lead to augmented proliferative activity towards transmembrane signals in B cells (46,47).
A marked increase on CIA incidence was evidenced after in vivo CR1 blockage. On the other hand, a similar enhanced incidence was observed in the group of animals that was treated with anti‐Ova monoclonal antibodies. At least, two arguments could explain this ambiguous response. The first one accounts for a potential bacterial contamination in the antibody batches used. Thus, different toll like receptor ligands of bacteria can activate a variety of antigen presenting cells including B cells and enhance antigen presentation, promote class switch recombination, expansion, and immunoglobulin secretion (48). The second argument lies on the potential triggering of an immune response against anti‐CR1 and anti‐Ova antibodies able to boost the reaction against BCII by activating the classical pathway of complement on the first days post BCII immunization. The increased CIA incidence observed in DBA/1 female mice transferred with cr2‐/‐ B cells supports the importance of CD35 as a regulatory receptor of B cell activation. Thus, lack of CD35 may lead to reduced regulation of the transferred B cells, increasing the risk of self tolerance breakage. On the other hand, the delayed CIA onset and astonishing low CIA incidence observed on cr2‐/‐ mice subjected to cr2+/+ B cell transfer, showed that these CD35/CD21 deficient mice were almost resistant to CIA development, suggesting that the expression of CD35 and CD21 on the injected B cells can protect mice from breaking tolerance against CII. Stronger evidence on the function of CD35/CD21 on B cells in the development of CIA will be obtained from new experiments including a higher number of animals per group.
The in vivo experiments performed during this project did not lead to statistically significant results giving clues about the role of CR1 and CR2 in CIA immunopathogenesis. Different regulatory mechanisms can be responsible of masking the potential effect of transferring either cr2‐/‐ or cr2+/+ B cells into cr2+/+ or cr2‐/‐ animals, respectively. A main aspect to be considered is the potential fading of anti‐BCII produced by few poorly‐expanded B cell clones in the spleen when measured in peripheral blood. Our group has found that the number of BCII‐specific IgM positive B cells in the spleen is low after the mice were immunized with BCII (data not published). Auto antibodies produced by these few B cells would be hardly detectable in the sera at day 11 post immunization. The role of B cells in CIA involves not only the production of antibodies against self antigens, but also the secretion of cytokines, the expression of co stimulatory molecules and antigen presentation to T
18
cells; as it is shown that the symptoms recovery in RA patients given B cell depleting therapy that does not eliminate plasmablasts (12).
An immune response against CD35 and CD21 is possibly evoked in cr2‐/‐ mice injected with cr2+/+ B cells. This anti‐CD35/CD21 immune response may be responsible of the depletion of the injected B cells, as well as of elimination of the protective effect of these cells to CIA some weeks after cell transfer and explaining perhaps the development of CIA in 25% of the cr2‐/‐ mice treated with cr2+/+ B cells at the end of the experiment. Additional experiments aimed to detect anti‐CD35/CD21 antibodies in cr2‐/‐ mice transferred with cr2+/+ B cells would confirm this hypothesis. The autoimmune prone phenotype observed in cr2‐/‐ mice, may also be explained by a defect of the more controlled and regulated B cell activation environment in the follicle compared to extrafollicular niches. The lacking of CR1 and CR2 promotes the accumulation of high molecular weight antigen at extrafollicular sites, leading to potential B cell activation in the absence of follicle‐specific cytokine and cellular milieu. Previous studies have shown that B cell activation and somatic hypermutation can take place at the T zone–red pulp border in the spleen of AM14 Id+ MRL/lpr mice. This genetically modified strain was designed to express a recombinant rheumatoid factor‐specific immunoglobulin gene (49). Outside the follicle, B cell activation and somatic hypermutation is driven by CD11c+ dendritic cells providing distinctive survival and differentiation signals to plasmablasts and B cells in a T cell independent fashion (13). A variety of experiments can be carried out to verify this hyphotesis. To begin with, the accumulation of BCII at the T zone‐red pulp boarder may be detected by histologic immunostaining using fluorochrome‐coupled polyclonal BCII. Additional histologic analyses can be made in BCII immunized cr2‐/‐ mice in order to evaluate the formation of extrafollicular clusters of plasmablasts at the bridging channel/red pulp boarder (50,51). Additionally, and to discard a potential regulatory signaling effect from CR1, anti‐CXCL13 can be used to block this chemokine on cr2+/+ B cells, preventing MZB cell‐dependent transport of high molecular weight antigens into the follicle (52).
5. Acknowledgements I am grateful to Professor Sandra Kleinau for her wise guidance along the project. The continuous support from my friends and lab partners Mike, Alex, Anja, Marius and Marlen are highly acknowledged. I thank my parents and brother for being constantly close to me even in the distance, their enthusiasm and love reached me despite the thousands of kilometers that lie between us. Adriana, to know that I have a friend like you always open to hear my trivial problems and frustrations was as important for the outcome of this project as knowing all the conceptual and technical issues behind it.
19
6. References
1. Firestein, G. S. (2005) J Clin Rheumatol 11(3 Suppl), S39‐44 2. Barton, A., and Worthington, J. (2009) Arthritis and rheumatism 61(10), 1441‐1446 3. Symmons, D. P., Barrett, E. M., Bankhead, C. R., Scott, D. G., and Silman, A. J. (1994) British
journal of rheumatology 33(8), 735‐739 4. Alamanos, Y., Voulgari, P. V., and Drosos, A. A. (2006) Seminars in arthritis and rheumatism
36(3), 182‐188 5. Tobon, G. J., Youinou, P., and Saraux, A. (2010) Journal of autoimmunity 6. McInnes, I. B., and Schett, G. (2007) Nature reviews 7(6), 429‐442 7. Jacobs, J. P., Wu, H. J., Benoist, C., and Mathis, D. (2009) Proceedings of the National
Academy of Sciences of the United States of America 106(51), 21789‐21794 8. Pernis, A. B. (2009) Journal of internal medicine 265(6), 644‐652 9. Koenders, M. I., Joosten, L. A., and van den Berg, W. B. (2006) Annals of the rheumatic
diseases 65 Suppl 3, iii29‐33 10. Stamp, L. K., James, M. J., and Cleland, L. G. (2004) Immunology and cell biology 82(1), 1‐9 11. Wegner, N., Lundberg, K., Kinloch, A., Fisher, B., Malmstrom, V., Feldmann, M., and Venables,
P. J. Immunological reviews 233(1), 34‐54 12. Silverman, G. J., and Boyle, D. L. (2008) Immunological reviews 223, 175‐185 13. Garcia De Vinuesa, C., Gulbranson‐Judge, A., Khan, M., O'Leary, P., Cascalho, M., Wabl, M.,
Klaus, G. G., Owen, M. J., and MacLennan, I. C. (1999) European journal of immunology 29(11), 3712‐3721
14. Wooley, P. H., Luthra, H. S., Stuart, J. M., and David, C. S. (1981) The Journal of experimental medicine 154(3), 688‐700
15. Hietala, M. A., Jonsson, I. M., Tarkowski, A., Kleinau, S., and Pekna, M. (2002) J Immunol 169(1), 454‐459
16. Nilsson, K. E., Andren, M., Diaz de Stahl, T., and Kleinau, S. (2009) Faseb J 23(8), 2450‐2458 17. Rossen, R. D., Brewer, E. J., Sharp, R. M., Ott, J., and Templeton, J. W. (1980) The Journal of
clinical investigation 65(3), 629‐642 18. Zipfel, P. F., and Skerka, C. (2009) Nature reviews 9(10), 729‐740 19. Carroll, M. C. (2004) Nature immunology 5(10), 981‐986 20. Reid, K. B., and Porter, R. R. (1981) Annual review of biochemistry 50, 433‐464 21. Roozendaal, R., and Carroll, M. C. (2007) Immunological reviews 219, 157‐166 22. Gal, P., Dobo, J., Zavodszky, P., and Sim, R. B. (2009) Molecular immunology 46(14), 2745‐
2752 23. Grant, E. P., Picarella, D., Burwell, T., Delaney, T., Croci, A., Avitahl, N., Humbles, A. A.,
Gutierrez‐Ramos, J. C., Briskin, M., Gerard, C., and Coyle, A. J. (2002) The Journal of experimental medicine 196(11), 1461‐1471
24. Endo, Y., Takahashi, M., and Fujita, T. (2006) Immunobiology 211(4), 283‐293 25. Torreira, E., Tortajada, A., Montes, T., Rodriguez de Cordoba, S., and Llorca, O. (2009)
Proceedings of the National Academy of Sciences of the United States of America 106(3), 882‐887
26. Bhakdi, S., and Tranum‐Jensen, J. (1978) Proceedings of the National Academy of Sciences of the United States of America 75(11), 5655‐5659
27. Schneider, M. C., Exley, R. M., Ram, S., Sim, R. B., and Tang, C. M. (2007) Trends in microbiology 15(5), 233‐240
28. Ahearn, J. M., Fischer, M. B., Croix, D., Goerg, S., Ma, M., Xia, J., Zhou, X., Howard, R. G., Rothstein, T. L., and Carroll, M. C. (1996) Immunity 4(3), 251‐262
29. Carroll, M. C. (2008) Vaccine 26 Suppl 8, I28‐33 30. Erdei, A., Isaak, A., Torok, K., Sandor, N., Kremlitzka, M., Prechl, J., and Bajtay, Z. (2009)
Molecular immunology 46(14), 2767‐2773
20
31. Barrington, R. A., Schneider, T. J., Pitcher, L. A., Mempel, T. R., Ma, M., Barteneva, N. S., and Carroll, M. C. (2009) Proceedings of the National Academy of Sciences of the United States of America 106(34), 14490‐14495
32. Phan, T. G., Grigorova, I., Okada, T., and Cyster, J. G. (2007) Nature immunology 8(9), 992‐1000
33. Roozendaal, R., Mempel, T. R., Pitcher, L. A., Gonzalez, S. F., Verschoor, A., Mebius, R. E., von Andrian, U. H., and Carroll, M. C. (2009) Immunity 30(2), 264‐276
34. Hasegawa, M., Fujimoto, M., Poe, J. C., Steeber, D. A., and Tedder, T. F. (2001) J Immunol 167(6), 3190‐3200
35. Reid, R. R., Woodcock, S., Shimabukuro‐Vornhagen, A., Austen, W. G., Jr., Kobzik, L., Zhang, M., Hechtman, H. B., Moore, F. D., Jr., and Carroll, M. C. (2002) J Immunol 169(10), 5433‐5440
36. Molina, H., Holers, V. M., Li, B., Fung, Y., Mariathasan, S., Goellner, J., Strauss‐Schoenberger, J., Karr, R. W., and Chaplin, D. D. (1996) Proceedings of the National Academy of Sciences of the United States of America 93(8), 3357‐3361
37. Kuhn, K. A., Cozine, C. L., Tomooka, B., Robinson, W. H., and Holers, V. M. (2008) Molecular immunology 45(10), 2808‐2819
38. Marquart, H. V., Svendsen, A., Rasmussen, J. M., Nielsen, C. H., Junker, P., Svehag, S. E., and Leslie, R. G. (1995) Clinical and experimental immunology 101(1), 60‐65
39. Wilson, J. G., Ratnoff, W. D., Schur, P. H., and Fearon, D. T. (1986) Arthritis and rheumatism 29(6), 739‐747
40. Isaak, A., Gergely, P., Jr., Szekeres, Z., Prechl, J., Poor, G., Erdei, A., and Gergely, J. (2008) International immunology 20(2), 185‐192
41. Jozsi, M., Prechl, J., Bajtay, Z., and Erdei, A. (2002) J Immunol 168(6), 2782‐2788 42. Mebius, R. E., and Kraal, G. (2005) Nature reviews 5(8), 606‐616 43. Pillai, S., Cariappa, A., and Moran, S. T. (2005) Annual review of immunology 23, 161‐196 44. Wang, J. H., Li, J., Wu, Q., Yang, P., Pawar, R. D., Xie, S., Timares, L., Raman, C., Chaplin, D. D.,
Lu, L., Mountz, J. D., and Hsu, H. C. J Immunol 184(1), 442‐451 45. Rickert, R. C. (2005) Current opinion in immunology 17(3), 237‐243 46. Engel, P., Zhou, L. J., Ord, D. C., Sato, S., Koller, B., and Tedder, T. F. (1995) Immunity 3(1), 39‐
50 47. Zhou, L. J., Smith, H. M., Waldschmidt, T. J., Schwarting, R., Daley, J., and Tedder, T. F. (1994)
Molecular and cellular biology 14(6), 3884‐3894 48. Bekeredjian‐Ding, I., and Jego, G. (2009) Immunology 128(3), 311‐323 49. William, J., Euler, C., Christensen, S., and Shlomchik, M. J. (2002) Science (New York, N.Y
297(5589), 2066‐2070 50. Herlands, R. A., William, J., Hershberg, U., and Shlomchik, M. J. (2007) European journal of
immunology 37(12), 3339‐3351 51. Weisel, F., Wellmann, U., and Winkler, T. H. (2007) European journal of immunology 37(12),
3330‐3333 52. Reif, K., Ekland, E. H., Ohl, L., Nakano, H., Lipp, M., Forster, R., and Cyster, J. G. (2002) Nature
416(6876), 94‐99