Disorders of the Immune System 2

Richard A. McPherson, M.D.

Cells of the Immune System

• Granulocytes/Neutrophils/Polymorphnuclear Granulocytes (PMNs, Polys)

• Lymphocytes

• Monocytes

• Eosinophils

• Basophils

Neutrophil in Peripheral Blood

Band (early neutrophil)

Lymphocytes

Atypical Lymphocytes (Viral Infection?)

Cellular Immune System (Lymphocytes)

• T-lymphocytes: CD2, CD3 markers• 60-70% of peripheral lymphocytes; also in

lymph nodes & spleen• T cell antigen receptor binds to CD3 complex• Somatic gene rearrangements (TCR)• T cell proliferations

– (Mono)Clonal = neoplastic– Polyclonal = non-neoplastic

Malignant Lymphocytes (Clonal)

T Cell Antigen Receptor Gene Rearrangement (Clonal)

T Lymphocytes• CD4+ helper T cells: secrete cytokines

– 60% of CD3+ T cells– TH1 induce cellular immunity– TH2 induce humoral immunity– CD4 binds MHC class II for Ag presentation

• CD8+ suppressor T cells: cytotoxicity– 30% of CD3+ T cells– CD8 binds MHC class I for Ag presentation– CD4/CD8 ratio ~2:1

Flow Cytometry: CD4, CD8; Normal

CD4

CD8

Flow Cytometry: CD4, CD8; Abnormal

Loss of CD4CD8

B Lymphocytes

• 10-20% of peripheral lymphocytes

• In bone marrow, lymph nodes, spleen, tonsils

• Antigen stimulation: form plasma cells

• Secrete immunoglobulins: IgM, IgG, IgA, IgD, IgE

• Ig antigen receptors on cell membranes of B cells

• CD19, CD20, CD21 = B cell markers

• EBV infects B cells (infectious mononucleosus)

• Medication Rituximab: Anti-CD20 against B-cell malignancies

Plasma Cell (rarely seen in blood)

Monoclonal Plasma Cell Disorders• Multiple myeloma (IgG, IgA)• Waldenstrom’s macroglobulinemia (IgM)• Monoclonal gammopathy of unknown

significance (MGUS)• Occasionally B-cell lymphoma• Finding a monoclonal spike in serum or urine

usually leads to bone marrow examination, etc.

Serum Protein Electrophoresis with Monoclonal Spike of Immunoglobulin

Confirmation by Immunofixation

Clonality by Electrophoretic Mobility

• Polyclonal ~ reactive, “normal” immune system response to stimulation (inflammation, infection)

• Monoclonal ~ autonomous, neoplastic clone of plasma cells

Alb 1 2 polyclonal

+ -

monoclonal

Scans of SPEP: Immunoglobulin Variations

Antigen Presentation• Macrophages

– Process and present antigens to T cells– Cytokine production– Immunosurveillance/delayed hypersensitivity

• Dendritic/Langerhans’ cells– Efficient Ag presentation: MHC class II on surface– Dendritic in lymphoid tissues– Langerhans’ in epidermis– Not phagocytic– Fc receptors for trapping Ags/immunologic memory

Granulocyte-Lymphocyte-Monocyte

Natural Killer (NK) Cells• 10-15% of peripheral lymphocytes

• No T-cell antigen receptors, no surface Ig

• Large granular (azurophilic) lymphocytes

• Lyse tumor, virus-infected cells without previous sensitization: 1st line of defense

• CD2+, CD3-, CD16+, CD56+

• CD16 = Fc receptor to target IgG-coated cells

• Antibody-dependent cell-mediated cytotoxicity, ADCC

Medication: Herceptin (trastuzumab)

• Anti-breast cancer antibody• Administered IV• Ab coats tumor cells that have Her-2 (epidermal

growth factor receptor 2 protein) on membrane surface

• Fc region of Ab sticks out• NK cells recognize the Fc regions and destroy

Ab-coated tumor cells by ADCC

Large Granular Lymphocyte

Cytokines• Mediate natural immunity/inflammation: IL-1,

TNF-• Lymphocyte growth, activation, differentiation:

IL-2, IL-4, IL-5, IL-12, IL-15, TGF-• Activate inflammatory cells (non-specific): IFN-

, TNF-, TNF-, MIF

• Chemotaxis: IL-8, eotaxin

• Hematopoiesis: GM-CSF, G-CSF, stem cell factor, IL-3, IL-7

New Medications for Immunomodulation• Anti-CD20 for B-cell malignancy

– Rituxan (rituximab)

• Anti-TNF- for rheumatoid arthritis, inflammatory bowel disease– Remicade (infliximab)– Enbrel (etanercept)

• Interferons– Gamma: stim immun– Alpha: HCV

• Granulocyte CSF: Neupogen (filgrastim)

Histocompatibility Genes (Ags)• Bind peptide fragments of foreign proteins for

presentation to T cells• Chromosome 6• Class I Ags: HLA A, B, C on nucleated cells• Class II Ags: HLA D; subregions DP, DQ, DR

on macrophages, B cells, activated T-cells, vascular endothelial cells, fibroblasts, renal epithelium; very complex identity

• Class III: genes that map between I and II (Complement C2, C3, Bf, TNF

Map of MCH Region on Chr 6

Fine Map of MHC Class II

HLA Complex• Human leukocyte antigens• Organ transplantation demonstrated barriers by

cellular and humoral immunity• Many alleles: antigenic diversity and identity• Class I present to CD8+ cytotoxic T cells• Class II present to CD4+ helper T cells• Modulation of immune response• Disease assoc: HLA-B27/ankylosing spondylitis;

DR4/rheumatoid arthritis; DR3/Sjogrens syn, diabetes

Structure of HLA Class I Ag:Heavy chain plus 2-microglobulin

Structure of HLA Class II Ag: 2 different heavy chains

Type I Hypersensitivity (Anaphylactic)

• Antigen binds to IgE on mast cells/basophils• Initial (5-30 min): vasodilatation, vascular leak, smooth

muscle spasm, bronchospasm, mucus secretion• Late (2-8 hrs): inflammatory infiltrate/tissue destruction• Primary mediators: vasoactive amines (histamine),

chemotaxis C3a, heparin, neutral proteases• Secondary: leukotrienes-vasoactive, spasmogenic,

prostaglandin D2-bronchospasm, mucus; PAF; cytokines

Medications

• Antihistamines

• Leukotriene receptor antagonists (LTRA)– Montelukast– Zafirlukast

• Epinephrine

• Steroids

• Methylated xanthines (theophylline)

Basophil: releases histamine

Release of Histamine

Type I Hypersensitivity:Clinical Examples

• Local reaction on skin/mucosa: urticaria, food allergies, hay fever, asthma

• Genetically controlled: atopy = familial disposition

• Benefit: protects against parasitic infections

Immunotherapy: Ragweed Pollen

Type II Hypersensitivity (Antibody Dependent)

• Target Ags on cell membranes• Complement-mediated reactions

– Transfusion reactions to incompatible blood group Ag– Rh incompatibility: Rh neg mother, Rh pos fetus; hemolytic

disease of newborn; Rhogam to all Rh- mothers with Rh+ babies

– Autoantibodies against RBCs, WBCs, platelets

• Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

• Antibody-mediated cellular dysfunction: autoantibodies against receptors

Type III Hypersensitivity (Immune Complex Mediated)

• Activation of complement; accumulation of granulocytes that cause damage

• Systemic: deposition of Circulating Immune Complexes in tissues– Bacteria, viruses, self-Ag (DNA), serum sickness– Kidneys, joints, skin, heart, serosa, small vessels– Vasodilatation, edema, destructive enzymes, tissue necrosis

• Local (Arthus reaction)– Acute immune complex vasculitis with tissue necrosis– Farmer’s lung to mold on hay

Necrotizing Vasculitis

Type IV Hypersensitivity (Cell Mediated)

• Delayed hypersensitivity by CD4+ T cells– Example: positive tuberculin skin test (intradermal)– Local erythema/induration in 8-12 hr, peak 2-7 d– Lymphocytes and monocytes migrate from vessels– Transformation to granuloma– Major defense against mycobacteria, fungi, parasites;

tumor immunity, transplant rejection– Cellular cytotoxicity by CD8+ cells

Organ Transplant Rejection (cellular)• T-cell mediated: 10-14 days

– Foreign HLA Ags on graft– CD8+ cytotoxic T lymphocytes– CD4+ T cells secrete lymphokines– Vascular permeability, mononuclear infiltrate, tissue

ischemia

• Medications: T-cell suppressants– Cyclosporine– Tacrolimus– Sirolimus– Rapamycin– Mycophenolic acid

Organ Transplant Rejection (Humoral)

• Antibody mediated– Hyperacute (mins to hrs): preformed Abs– Anti-HLA Abs form with T cell response– Acute and chronic rejection

• Treatment: plasma exchange to remove Abs

Transplantation• HLA match between donor and recipient

• Immunosuppression: cyclosporine, FK-506, ALG

• Solid organs: kidney, heart, lung, pancreas, liver

• Bone marrow transplant: CD34 stem cells– Autologous/allogeneic– Graft vs host disease (GVHD): liver, skin, intestine

(undesired)– Graft vs tumor (leukemia) effect (desired)