Adaptive Immunity. Jeffrey K. Actor, Ph.D. MSB 2.214,

Transcription

1 Adaptive Immunity Jeffrey K. Actor, Ph.D. MSB 2.214,

2 Lecture Objectives: Understand role of various molecules including cytokines, chemokines, costimulatory and adhesion molecules in the development of adaptive immune responses To describe the various effector and regulatory functions of T and B cells To demonstrate the molecular events associated with T cell and B cell activation To develop a practical understanding of mechanisms and clinical relevance of T-dependent and T-independent antibody responses.

3 Normal Immune Physiologic Functions Preserve homeostasis by host defense Environmental challenges Neoplastic, damaged cells Discerns Self vs. non self Pathogenicity Intracellular vs. extracellular assaults Begins in utero Remembers previous encounters (vaccine) Goal for Health Specificity Intensity Duration

4 Clonal Selection of Adaptive Immune Cells Acquired immunity involves: Specificity, Memory, Adaptiveness, Self vs Nonself Occurs as a result of random selection of V region components during development. Clonal Selection process: Naïve T/B cells of all specificities prior to antigen contact Each lymphocyte has single antigen receptor Clonal expansion occurs with antigen stimulation under ideal conditions self lymphocytes deleted or inactivated

5 Development of Adaptive Response Regulated by Cytokines Small molecular weight glycopeptides Made by a variety of cells Monocytes, dendritic cells and other APC Lymphocytes, mast cell/basophils, eosinophils Epithelial/endothelial/fibroblasts Each cytokine has multiple activities [plieotropic], dependent upon cell target, concentration, and presence of other cytokines Multiple cytokines can have the same function [redundancy] Cytokines can modulate function by stimulating/inhibiting cell populations.

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7 Cytokines Classification based upon Function Interferons (,, ) Interferes with viral replication Immunomodulators Colony stimulating factors Hematopoietins Inflammatory mediators Tumor necrosis factors (, ) Hemorrhagic necrosis of tumors Mediators of inflammation/sepsis Chemokines Chemotaxis of various inflammatory cells Interleukins Immunomodulations between WBC Inter = between; leukin = leukocyte

8 T cells Thymus derived or thymic dependent Functions Cell mediated immunity Immunoregulation Characterized with surface marker CD3 Functional subgroups > CD4 = helper > CD8 = cytotoxic Surface markers regulate activation and immune function

9 CD45RO / CD45RA Memory marker / Naïve marker

10 T helper cells CD4+ MHC class II restricted Primary regulators of the B and T cell responses Help B cells proliferate/differentiate to plasma cells or Help T cells proliferate/differentiate to effector (CTL) and/or delayed type hypersensitivity

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12 Activation Requirement for Co-stimulation Step 1 Ag-MHC + TCR + CD4 Presence of specific cytokines Step 2 Adhesion molecule pairings CD58/CD2 ICAM-1/LFA-1 Step 3 Costimulatory molecule pairings CD40/40L (CD154) (CD80 or CD86) with (CD28 or CTLA4) APC/Tcell

13 Major subsets of CD4 + T cells: T H 1, T H 2, T H 17, and T reg.

14 The Th1/Th2 Paradigm: Regulation of Balanced Response Factors that push to develop to Th1 Th0 Regulatory cytokines Factors that push to develop to Th2 Th1 Regulatory cytokines Th2 Cytokines to help Cellular Immune Function Balance Cytokines to help Humoral Immune Function Intracellular Pathogens Extracellular Pathogens

15 The Th1/Th2 Paradigm: Regulation of Balanced Response IL-4 IL-12, IL-18 IFN- Th1 Th0 IFN- Th2 IL-4 IL-12 IFN- Balance IL-4 IL-5 Intracellular Pathogens Extracellular Pathogens

16 IFN- TH1 / TH2 PARADIGM Differential cytokine patterns TH1 -> cell mediated immunity TH2 -> humoral mediated immunity IL-4 Intracellular Pathogens Extracellular Pathogens

17 Cytokines influence the differentiation into a particular subset of CD4 + T cells. Cytokines synthesized by one subset of CD4 + T cells inhibit the development of other subsets.

18 T Cells Activation Intracellular Events TCR Binding CD3 transduction across membrane Tyrosine kinases (Fyn, Lck) -> ZAP-70 ZAP-70 -> PLC- to split PIP 2 into DAG and IP 3 Nuclear signal transfer via transcription factor cascade NF- B, NF-AT Chromosome activated and genes transcribed Cell activated (cytokines, receptors, effectors)

19 No need to memorize full cascade on p125 and 126 of syllabus for this block exam.

20 Other Events of T cell Activation Expression of molecules that allow cells to readily traffic from Lymph Node Increased adhesion molecule expression Promotes migration into tissues

21 T cell Activation/Migration Blood Rolling Adhesion Migration Selectins Integrins Endothelial Cell Tissue Mast Cell T-Cell Chemoattraction IL-3,5 GM-CSF Chemokines Survival and Activation GM-CSF Tissue Cells Extracellular matrix IL-2, 4 GM-CSF Rothenberg ME. N Engl J Med 1998;338:(22)

22 T cell Costimulatory Pairs: Promotes T Activation APC T cell CD40 - CD40L(CD154) B cell activation and isotype switch CD80/86 (B7.1, 7.2) - CD28 CD80-CD28 : favors TH1 development CD86-CD28: favors TH2 development Bypassing CD28 induces tolerance CD80/86 - CTLA4 Induces tolerance

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24 Generation and Function of Cytotoxic T Lymphocytes (CTL) Will cover in next lecture.

25 Cytotoxic T Lymphocytes (CTL) CD8 + MHC-I restricted Upregulated by TH1 activity (IFN, IL-2) Mediates CMI Viral infection, intracellular pathogens Tumor cells

26 CTL Mechanisms of Target Cell Killing Perforins Transmembrane channels Related to complementmediated lysis Granzyme formation Upregulated by IFN Activates target cell apotosis CD95/95L (Fas/FasL) Memory cell formation after process complete

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28 CTLs: Additional Note Affected by TH1 cells Provide help IFN- and IL-2

29 CD4+ Cells Give Help to CTLs + Viral proteins from cells in local area

30 Coico Figure

31 Cytotoxic Cell Comparison: CTLs Antigen specific and MHC Class I restricted. Express CD8. CTLs kill their targets by using Perforin, Granzymes, Cytokines, Fas and Fas ligand. NKT cells Antigen specific and CD1 restricted. Recognize lipid and glycolipid antigen. Have a limited TCR repertoire. IFN-, IL-2, TNF- α production when activated. Make up <0.2% of peripheral blood T cells.

32 Cytotoxic Cell Comparison: NK cells - nonspecific (no T cell receptor). Morphologically large granular lymphocytes (LGLs). Non-T and non-b lymphocytes lacking surface CD3, CD4, CD8 and CD19. Do not express immunoglobulins or TCRs. Express CD16 and CD56. Kill by perforin, granzymes and cytokines (IFN- and TNF). NK-ADCC Antibody-dependent cellular cytotoxicity (ADCC). Have Fc receptors (CD16) that recognize Fc portion of IgG Lymphokine activated killer cells (LAK cells) Morphologically LGLs. Non-T non-b lymphocytes.

33 Other ways to activate T Cells Lipids/glycolipids Superantigens Mitogens

34 Mitogens: Any substance that stimulates mitotic division Polyclonal activators of T cells Derived from plant lectins reacts with surface sugars to agglutinate cells Phytohemagglutinin (PHA) Concanavalin A (Con A) Pokeweed mitogen (PWM) Other mitogens LPS endotoxin human monocytes, macrophages, dendritic cells Anti CD3 polyclonal T cell activator

35 B cells

36 B cells Bursal equivalent (bone marrow derived) lymphocytes Make antibody, differentiate to antibody secreting plasma cells Has maturation/differentiation that is both antigen (Ag) independent and dependent Markers on B cells include CD19 and CD21 Has surface Ig receptors Activation to secrete antibody is Ag dependent B cells can act as APCs to present Ag to T cells

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38 T cell- B cell Cooperation: T Dependent Antigens T dependent antigens Require CD4+ cell response to help to make antibody Recognition by BCR, presentation to TCR through B cell surface MHC

39 Activation of B cells by T cells Note: CD40 CD40 Ligand pair requisite for isotype switching. Case #2. Geha and Notarangelo Individuals with mutation in CD40L can only make IgM and IgD

40 One antigen-specific T cell can initiate differentiation for multiple B cells with different antibody specificities!

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42 T cell- B cell Interactions Response does not require a secondary APC B cells can present directly to T cells Cytokine requirements B cell growth (IL-4) and proliferation (IL-6) Isotype switch IgG -IFN IgE IL-4, IL-13 IgA IL-5 IgM is Ag receptor that binds external Ag B cell T cell Internalized, processed and presented via MHC II to CD4 Costimulation required (CD40 - CD154; CD80/86 CD28) Adhesion (CD58 - CD2; ICAM-1 - LFA-1) Cytokine from T cell binds to B cell surface receptors to assist

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44 T independent antigens Do not require T cells for antibody production Antigen is typically polymerized antigen (i.e. polysaccharides) with repeating epitopes Only produce IgM isotypes Does not generate immunological memory

45 B cell activation pathways: T cell Independent Surface IgM is cross-linked Signal transduction occurs across membrane Tyrosine kinases (Fyn, Lck) -> Syk Syk -> PLC- to split PIP 2 into DAG and IP 3, -> Activation of calcineurin and kinases Nuclear signal transfer via transcription factor cascade NF- B, NF-AT Chromosome activated and genes transcribed Cell activated -> upregulation of cytokine receptor and immunoglobulin synthesis

46 T helper B cell cooperation: Utility of conjugate vaccines Polysaccharide alone, e.g., the purified capsular polysaccharide of H. influenzae or S. pneumoniae, generates IgM in a thymus-independent response Polysaccharide conjugated to a carrier protein such as tetanus toxoid generates a thymus-dependent IgG response.

47 Intracellular events in B-cell activation. No need to memorize full cascade on p134 of syllabus for this block exam.

48 Adaptive Immunity Summary Cytokines are small molecular weight glycopeptides variety of cellular origins and functions; redundant/pleiomorphic. CD4+ Helper T cells provide assistance for immune responses Multiple subsets producing/controlled by unique subset of cytokines. Subset development controlled by environmental cytokines. CD8+ CTLs confer cytotoxic function T cell antigen receptors can be activated by proteins, lipids/glycolipids, superantigens and mitogens B cells make antibodies; the quantity and isotype is dependent upon the nature of the antigen Most responses are T-dependent with help from T cell cytokines. T-independent responses relate to specific repeating epitopes (eg. polysaccharides); are only IgM and do not generate memory.

49 The Th1/Th2 Paradigm: Regulation of Balanced Response IL-4 IL-12, IL-18 IFN- Th1 Th0 IFN- Th2 IL-4 IL-12 IFN- Balance IL-4 IL-5 Intracellular Pathogens Extracellular Pathogens

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52 T Helper Cells: Functional Subclasses

53 (CD40L) (CD80 / CD86) (LFA-3) (CD54) (CD11) CD45RO CD45RA Memory marker Naïve marker