FUNCTIONS AND DYSFUNCTIONS OF THE IMMUNE SYSTEM WITH EMPHASIS ON THE CNS

1. FUNCTIONS AND DYSFUNCTIONS OF THE IMMUNE SYSTEM WITH EMPHASIS ON THE CNS

2. Normal functions and disorders of the immune system • Normal functions • Immunity against microorganisms and pathogens • Wound healing • Tumor surveillance • Disorders from immune dysfunction • Autoimmunity • Immune mediated disorders • Bystander damage • Graft rejection

3. The innate immune system Skin Phagocytes PMNS Monocytes Macrophages Natural killer (NK) cells Acute phase reactants Compliment system Adaptive immune system Antibodies Recognize free antigen Fab and Fc B cells Antigen binding stimulates B cell proliferation Most B cells express MHC II Function also as APC T cells Promote B cell maturation and Ab prouction Produce cytokines to enhance innate immune system Antigen presenting cells The immune system

5. Components of the immune system

6. Components of the immune system • Monocytes and macrophages • 4% of the peripheral blood leukocytes • Contain many enzymes for • Killing • Processing antigens • Monocytes differentiate into tissue specific macrophages • Natural killer cells • 2% of peripheral blood leukocytes • Synonymous with large granular lymphocytes • Lack immunological memory • Kill viral infected cells and tumor cells • Do not need MHC for normal function • NK1+T cells • Express both TCR and NK1.1 receptors

7. Components of the immune system • T lymphocytes • Originate from the thymus • Has unique specificity for recognizing antigens • Generally classified into two groups • CD4+ involved in DTH and B-cell differentiation • CD8+ involved in class 1 restricted lysis of antigen-specific targets • T cells with suppressor activity can express both CD4 or CD8

9. Components of the immune system • T cell receptors • Are composed of alpha and betha glyocsylated polypeptide chains • Each chain is composed of V ,J and C regions resembling Igs • There are about 100 TCR –variable genes • T cells can only recognize short peptides associated with MHC • They also express non polymorphic antigens on their surface • The most abundant of which is CD45

11. Components of the immune system • B LYMPOCYTES • Are precursors of antibody secreting cells • Cells develop in the bone marrow • Contain specific Ig receptor that commit them to recognize specific antigen • They commonly express IgM on their surface but switch to other isotypes with the help of T cells • Following antigenic challenge T cells help B cells • Cognate interaction • Non cognate interaction

13. Components of the immune system • Immunoglobulin • Are glycoprotein that are the secretory product of the plasma cells • Are composed of two light chains and two heavy chains • According to the chemical nature of the heavy chain they are divided into • A, G, M ,D and E • React with peptides , proteins ,lipids • Each heavy and light chain are composed of • Constant region – carboxy terminal (Fc portion) • Fc portion binds to the host tissue and fixing compliment • Variable region –amino terminal and form Fab portion • Immunoglobulin are important for • Antibody dependant cells-mediated cytotoxicity • For compliment mediated cell lysis • Not all immunoglobulin fix complement • IgM ,IgG1 and IgG3

15. Diversity of antigen receptors Due diversity of V,(D) and J gene segments Recombination inaccuracies at the joining sites of the V,D and J regions Somatic mutation of B cells after antigen binding This phenomenon does not occur in T cells MHC/HLA Distinguish self from non self Present antigen to the appropriate cells MHC class I Alpha chain of MHC gene small Beta chain non MHC gene HLA-A , HLA-B and HLA-C Regulates specificity of cytotoix T cells MHC class II Alpha Betha HLA –DP , DQ and DR Regulates specificity of T helper cells Genetics of the immune system

18. Organization of the immune response • Initiation of the immune response • Antigen presentation • Accessory molecules for T cell activation • Costimulatory molecules • Regulation of the immune response • Cytokines • Chemokines • Termination of the immune response • B cell inhibition • Immunoglobulin • T cells

19. Initiation of the immune response • Antigen presentation • monocytes macrophages • B cells • Dendrite cells • Glial cells • Accessory molecules for T cell activation • Involved in recognition, activation, intracellular signaling ,adhesion and trafficing • CD3 • It is part of the TCR complex • Primarily involved in signaling for T cell activation and proliferation through ITAM • CD4 and CD8 • Plays an accessory role in signaling and antigen recognition • CD4 binds with the non polymorphic portion of beta MHC II • Non T cells that expressCD4 : microglial cells and macrophages • CD8 binds with the non polymorphic portion of alpha MHC I • CD19 found in B cells

20. Initiation of the immune response • Costimulatory molecules • B7- CD28 , CD40 - CD154 • B7- CD28 secrete IL2 and express Bcl-x anti- apoptotic molecule • CTLA-4 homologous of CD28 and it inhibit T cell activatiion • The integrin family : VCAM-1 ,ICAM-1, LFA-1 , CD45 and CD2 • Also mediate T cell adhesion and guides cell trafficking • L-selctin , matrix metalloprotinase (MMP) and CD44 • Homing receptor • facilitates T cell entry into target peripheral lymphoid organ

22. Cytokines • Growth factors • IL-1 IL-2 IL-3 IL-4 and colony stimulating factors • Activation factors • Interferon alpha, beta and gamma • Regulatory or cytotoxic factors • IL-10, IL-12 ,TGF-B and TNF-alpha • Are necessary for T cell activation , amplification and modulation of immune response • T helper 1 cells • secret INF-gamma, IL-2 and TNF –alpha • T helper 2 cells • IL-4 IL-3 IL-6 IL-10 and IL-13 • T 3 cells • TGF beta

24. Chemokines • Aid in leukocytes directed mobility • Two families • C-C FAMILY :MCP MIP-1, RANTES • C-X-C FAMILY: IL-8 • They are produced by immune and non immune cells • Monocytes , T cells , basophils and eosinophils express receptors for chemokines • CCR5 CXCR4 act as coreceptor for HIV

27. Regulation of the immune response • Termination of the immune response • B cell inhibition • Clearance of antigen by the reticuloendothelial system or through the formation antigen-antibody complex • Binding of the Ag –Ab complex with Fc receptor on to the CD32 of B cells results in the inhibition of B-cell differentiation • Immunoglobulin • Anti-idiotypic response to the variable region of the Ig and TCR • T cells • Anergy • Deletion • Suppressor cell activity

28. Self-Tolerance • Central tolerance • Positive selection • On the cortex of thymus • T cells with no affinity to MHC will die of lack of signal activation • Those with MHC survive and become single positive thymocyts • Negative selection • In the thymus medulla • Those cells that display a high affinity to self antigen are deleted by apoptosis

29. Self Tolerance • Peripheral tolerance • Anergy • Signal one = APC with its peptide + MHC • In the absence of signal one cell die of neglect • Signal two = co stimulatory signals • In the absence of signal two T cells become anergic • Expression of alternate co stimulatory molecule by activated T cells CTLA- 4 • IT occur when antigen is presented by non professional APC

31. Self-Tolerance • Peripheral Tolerance • Apoptosis • Programmed cell death • Signals of apoptosis • Withdrawal of growth factor or cytokines • Exposure to corticosteroids or repeated antigen contact • Mediatiors of apoptosis • Anti apoptotic genes = Bcl family of genes • Proapoptotic genes = Fas family of genes • Activated T cells express Fas-ligand and Fas • Activation induced cell death • Cytokines • IL-2 , TNF –alpha , INF-gamma

33. Self-Tolerance • Suppressor T cells • Dawn regulate CD4 or CD8 cells • T suppressor cells can be • CD4/8 • Are antigen specific • Mediate suppression • through the production of modulating cytokines • Th2 • TGF –beta • expression of negative regulatory molecules • CTLA-4

34. Laboratory Evaluation of Host Defense Status • Initial Screening Assays • Complete blood count with differential • smearSerum immunoglobulin levels: IgM, IgG, IgA, IgD, IgE • Other Readily Available Assays • Quantification of blood mononuclear cell populations by immunofluorescence assays employing monoclonal antibody markersb •  T cells:  CD3, CD4, CD8, TCRαβ, TCRγδ   • B cells:  CD19, CD20, CD21, Ig(µ, δ, γ, α, κ, λ), Ig-associated molecules (α, β)  Activation markers: HLA-DR, CD25, CD80 (B cells), CD154 (T cells)  •  NK cells:  CD16/CD56   • Monocytes:  CD15

35. T cell functional evaluation   • 1. Delayed hypersensitivity skin tests (PPD, Candida, histoplasmin, tetanus toxoid)   • 2. Proliferative response to mitogens (anti-CD3 antibody, phytohemagglutinin, concanavalin A) and allogeneic cells (mixed lymphocyte response)  •  3. Cytokine production • B cell functional evaluation •   1. Natural or commonly acquired antibodies: isohemagglutinins; antibodies to common viruses (influenza, rubella, rubeola) and bacterial toxins (diphtheria, tetanus)   • 2. Response to immunization with protein (tetanus toxoid) and carbohydrate (pneumococcal vaccine, H. influenzae B vaccine) antigens  •  3. Quantitative IgG subclass determinations

36. Complement   • 1. CH50 assays (classic and alternative pathways)   • 2. C3, C4, and other components • Phagocyte function •   1. Reduction of nitroblue tetrazolium   • 2. Chemotaxis assays  •  3. Bactericidal activity

37. The Immune system and the CNS • The CNS has been termed immune privileged site • Absence of lymphatic drainage • BBB • Low level of MHC factors in the resident cells of the CNS • Lack of potent antigen presenting cells • Presence of immunosuppressive factor (TGF-beta)

38. Conditions perturbing the immune privilege • Entry of inflammatory cells through BBB is facilitated by • Up regulation of adhesion molecules on endothelial cells • VCAM • ICAM • Activation T cells • Enhanced MHC expression by CNS resident cells in the presence of • Cytokines • TNF alpha • IFN gamma • Under inflammatory condition • APCs microgllial cells are the principal • Secret cytokines • Express costimulatory molecules • High levels of TGF beta and Fas ligand expression dawn regulate the immune system in the CNS • Important in CNS tumor pathogenesis

39. Mechanisms Preventing Autoimmunity • Sequestration of self-antigen • Generation and maintenance of tolerance    • a.   Central deletion of autoreactive lymphocytes    • b.   Peripheral anergy of autoreactive lymphocytes   •  c.   Receptor replacement by autoreactive lymphocytes • Regulatory mechanisms

40. Mechanisms of Autoimmunity • I.  Exogenous •   A.  Molecular mimicry •   B.  Superantigenic stimulation •   C.  Microbial adjuvanticity •  II.  Endogenous •   A.  Altered antigen presentation •     1.  Loss of immunologic privilege •     2.  Presentation of novel or crytic epitopes (epitope spreading) •     3.  Alteration of self-antigen •     4.  Enhanced function of antigen-presenting cells •       a.  Costimulatory molecule expression •       b.  Cytokine production •   B.  Increased T cell help •     1.  Cytokine production •     2.  Costimulatory molecules •   C.  Increased B cell function •   D.  Apoptotic defects •   E.  Cytokine imbalance •   F.  Altered immunoregulation

41. Human Autoimmune Disease: Presumptive Evidence for an Immunologic Pathogenesis • Major Criteria • Presence of autoantibodies or evidence of cellular reactivity to self • Documentation of relevant autoantibody or lymphocytic infiltrate in the pathologic lesion. • Demonstration that relevant autoantibody or T cells can cause tissue pathology  •  a.  Transplacental transmission  •  b.  Adaptive transfer into animals  •  c.  In vitro impact on cellular function • Supportive Evidence • Reasonable animal model • Beneficial effect from immunosuppressive agents • Association with other evidence of autoimmunity • No evidence of infection or other obvious cause

42. Autoimmune disease • Immune mediated diseases • Multiple sclerosis • Autoimmune diseases • Classified as • T cell mediated • MS , CIDP , Polymyositis • B cell mediated • Lambert-Eaton syndrome • Combination of both • Myasthenia Gravis

43. Multiple sclerosis • Females are affected 2:1 • Is a complex polygenic disease • Associated with HLA-DR2 • Environment • Immune system in MS • Presence of OCB • Reactivity to various myelin antigens • Activation of myelin specific-T cells through molecular mimicry or super antigen in the periphery • Th1 mediated disease • Interferon –beta • Increased production of IL10 by macrophages dawn regulate Th-1cells • Decrease production of IL-12 by macrophages • modulate adhesion molecule expression • Changing cell associated VCAM In to soluble VCAM • Dawn regulate co stimulatory molecule expression • Copaxone • A synthetic molecule that resemble myelin • Binds with MHC grove and is believed the T cells to wards these structure are biased toTh2 cells

44. Acute disseminated encephalomyelitis • A monophasic demyelinating disease • Associated with vaccination or • Rabies and small pox vaccines which were prepared with neural tissues • Molecular mimicry is the most likely mechanism • systemic viral infection (Parainfectious variant) • Measles ,rubella , mumps ,and several other viral infections • Its pathology closely mimic that of MS

45. Immune mediated neuropathies • AIDP • Pathology • Perinural infiltration by lymphocytes , monocytes ,and macrophages • Auto antibodies to GM1, Gd1a , and Gd1b • It is primarily an antibody mediated disease • Improvement by plasmapheresis • Demyelination up on transfer of immunoglobulin to experimental animal • Occurrence of AIDP has been linked with many infections • C. jejuni is one of the most commonly identified agent • Autoantibodies identified in GBS patients GMI , Gd1a ,Gd1b , and Gq1b • Herpes , M .pneumonia and many other bacterial and viral infefctions • CIDP • No specific autoantibody has been identified • Histopathological picture • is similar with AIDP • but wit fewer inflammatory cells • Onion bulb appearance • Indirect evidence that it is T cell mediated disease

46. Autoimmune Myasthenia Gravis • Autoimmune disease • 80-90 % cases have detectable auto antibodies to AChR • Most cases occur in females • Thymomas occur in 10- 15 % of patients • 75% of patients will have some thymic abnormality (thymic hyperplasia ) • Hyperplastic thymic cells over express V beta 5.1+TCR T cells • Often associated with other autoimmune diseases • Thyroid disorder • Rheumatoid arthritis • Pernicious anemia • SLE • Auto reactive T cell are necessary for the disease to occur • Failure of central tolerance may play an important role in disease pathogenesis • Removal of the thymus results in improvement of disease in 80-90% of patients • B cells are effectors • Genetics • HLAB8 and DDRw3 • Rx • actylchloinesterase inhibitors , IVIG ,plasmapheresis ,corticosteroids ,immunosuppressive ,and thymectomy

47. Inflammatory Muscle disease • PM ,DM , and IBM are immune mediated diseases • PM • Is thought to be caused by many causes : systemic autoimmunity , connective tissue disorder and viral and bacterial infection • Pathologically x-ed by • endomysial CD8 cell infiltrates • Relative sparing of blood vessels • Anti jo-1 antibody in upto 30% patients • DM • Perifacicular atrophy secondary to microvascular damage • Capillary damage is mediated by complement • Anti jo-1 antibody in upto 30% patients • IBM • Damage is mediated by CD8 T cells • Autophagic vacuoles • Amyloid deposites

48. Mediated by antibodies in reaction to tumor antigen Autoimmune disease Paraneoplastic Syndromes

49. Tumor immunology • Tumor immunosurveillance • Prevent or inhibit tumor growth • The main effectors are : CTLs, NK and TNF-alpha producing macrophges • Tumor cells escape surveillance mechanisms by • Masking or modulating antigens on their surface • Dawn regulation of classI andII MHC • Producing immunosuppressant like TGF –beta • Expressing high level of FasL allowing for local apoptosis • Therapeutic strategies • Vaccination with Tumor cells or antigen • Transfect tumor cells with plasmids congaing costimulatory molecules • Injection of tumor cells with cytokines such as IL-2 and TNF –alpha • Introduction of lymphokine activated cells (LAC)