Cell-Mediated immunity …………………………………….ppt
- 1. Cell - mediated immunity. (CMI.) Prof.Mohamed Osman GadElRab. College Of Medicine & KKUH.
- 2. Adaptive immunity have two effector mechanisms : 1.Humoral ( mediated by antibodies ) the primary domain of antibody protection lies outside the cell. ( extracellular infections ) 2.Cellular ( mediated by cells ) cell-mediated immunity detect & eliminate cells that harbor intracellular pathogens .
- 3. The principal role of cell-mediated immunity is to: • 1. detect and eliminate intracellular pathogens. • 2. recognize and eliminate tumor cells.
- 4. Both antigen- specific and non-specific cells contribute to cell-mediated immunity. . Specific cells include: • 1.CD8 cytotoxic T-lymphocytes. ( Tc cells or CTLs ) . • 2. CD4 Th cell.( cytokine –secreting ).
- 5. Non-specific cells include : 1. NK-cells . 2. macrophages . 3. neutrophils . 4. eosinophils .
- 6. Cell-mediated immune responses can be divided into two major categories: 1. Effector cells that have direct cytotoxic activity . 2. Effector CD4 T-cells that mediate Delayed-type hypersensitivity.
- 7. The activation requirements of T-cells. • The activation of naïve T-cells & their subsequent : 1.proliferation. and 2.differntiation. into effector T-cells require.
- 8. Two signals : • 1.Primary signal, when TCR interact with peptide-MHC complex (antigen ). • 2.Co-stimulatory signal, delivered by antigen presenting cell (APC ).
- 9. Critical Role of Th Cells in Specific Immunity • Select effector mechanisms. • Induce proliferation in appropriate effectors. • Enhance functional activities of effectors. APC Th cell B cell Tc cell NK Ag Ag Ag NK cell Cytokines Granulocyte Macrophage Antigen-presenting cell
- 10. Th1 cells & Th2 cells. • Depending on : 1. nature of antigen. 2. cytokines. Th 0 cells ( naïve cells, uncommitted) Take the Th1 pathway & produce cellular immunity. OR : the Th2 pathway & produce humoral immunity.
- 11. Naïve Th Cells Can Differentiate Into Th1 or Th2 Cells ThP cell ThO cell Th1 cell Th2 cell ThM cell IL-2 IFNγ IL-2 IL-4 IL-5 IL-10 IL-4 IL-5 IL-6 IL-10 IL-2 IFNγ IL-2 Naive Th cells Short-term stimulation Chronic stimulation Long term Memory cells
- 12. Functions of Th1 and Th2 Cells Th1 cell Th2 cell Macrophage B cell IFNγ Activates IL-4 IL-5 IL-10 Activates Inhibits production Mast cell Eosinophil Antibodies (including IgE)
- 13. Cell-adhesion molecules facilitate TCR interactions : • CD2 & the integrin LFA-1 ( on the surface of T-cells) bind respectively to : LFA-3 & ICAMs (intracellular) ( on antigen presenting cells )
- 14. Effector T-cells express a variety of molecules : • 1.Membrane- bound molecules include: -Fas ligand on CD8 CTLs. -TNF-B (tumor necrosis factor) on Th1 cells . -CD 40 ligand on Th2 cells.
- 15. 2. Soluble effector molecules include : - CTLs secrete cytotoxins ( perforins and granzymes ) . also secrete : IFN-gamma & TNF-B.
- 16. The Fas ligand , perforins & granzymes mediate: Target - cell destruction. • The TNF-B &IFN –gamma promote: Macrophages activation .
- 17. Cytotoxic T-cells • Cytotoxic T-cells (or CTL) are CD8+ cells & are therefore: class 1 MHC restricted . ( in rare instances CD4+ class11 restricted T-cells have been shown to function as CTLs )
- 18. Cytolytic T (Tc) Cells • Tc exiting the thymus are pre-Tc cells, i.e. have TCR that can recognize antigen, but are not mature and cannot kill until “armed”. • To become armed requires two signals: 1. Recognition by TCR of specific antigen associated with class I MHC, and 2. Exposure to cytokines (IL-2 and IFN-γ).
- 19. Role of Th1 cells in generation of CTLs. The interaction of Th 1 cells with APC result in production of IL -2 . * IL-2 act on CTL precursor cells and cause them to proliferate and differentiate into active CTLs.
- 20. Features of cytolytic T- cell Killing. • Antigen - specific. • Requires cell- cell contact. • Each Tc capable of killing many target cells.
- 21. Main Mechanism of Tc Killing • Tc granules contain perforin and granzymes. ( fragmentins ) • Upon contact with target cell, granule contents released, perforin polymerizes and forms channel in target cell membrane. • Granzymes (serine proteases) enter target cell through channel, activate caspases and nucleases, lead to apoptosis of target cell.
- 22. Steps in Tc Killing Tc cell 1. Tc recognizes antigen on target cell Target cell Tc cell 2. A lethal hit is delivered by the Tc using agents such as perforin or granzyme B Target cell Tc cell 3. The Tc detaches from the target cell Target cell 4. Target cell dies by apoptosis Target cell
- 23. Mechanism of Tc Killing Tc cell Ca++ Perforin monomers Perforin polymerizes Polyperforin channels Tc cell Target cell Granzymes Target cell
- 24. Mechanisms of Tc cytotoxicity • Tc kill using a variety of mechanisms: –Direct cell-cell signaling via surface molecules . –Indirect signaling via cytokines.
- 25. Mechanisms of Tc cytotoxicity (continued) • Tc can kill via Fas or tumor necrosis factor (TNF) receptor on a target cell (Signaling through Fas or TNF R.) • Tc express Fas ligand (FasL) on their surface. • Fas ligand interact with Fas (on target cells) and trigger: apoptosis.
- 26. Mechanism of Arming Tc Cells Pre-Tc cell Tc cell T helper cell Class I MHC Class II MHC APC 1. Cell expressing class I MHC presents antigen ( ) to a pre-Tc cell IFN IL-2 2. Antigen-presenting cell presents antigen in association with class II MHC to Th cell 3. Th cell makes cytokines 4. Pre-Tc cell differentiates to functional Tc cell 5. Tc recognizes antigen on class I MHC-expressing target cell 6. Target cell is killed
- 27. Fas/FasL and TNF killing by CTLs • Binding of ligand to receptor leads to induction of apoptosis through death domains (dd). • Receptors without dd do not lead to apoptosis.
- 28. Ligation of receptor leads to trimerization of the receptor and initiation of the caspase cascade Apoptosis = Programmed cell death = cell suicide.
- 29. Macrophage Activation Two major mechanisms activate macrophages : • IFN-γ produced by Th or Th1 cells plus bacterial endotoxin (LPS). • IFN-γ produced by Th or Th1 cells plus TNF-α.
- 30. Macrophage Macrophage Th cell Macrophage Cytokines Lymphokines Cytokines Anti-microbial functions Anti-tumor functions Invading agent Antigen presentation Activated macrophage Central Role of Macrophages in Natural and Specific Immunity. • Involved in initial defense and antigen presentation and have effector functions.
- 31. Mechanism of Macrophage Activation. Macrophage Activated Macrophage Bacterial endotoxin (lipopolysaccharide) triggers cytokine production Th1 cell 1 IFN gamma IFN gamma 2 Macrophage Activated Macrophage TNF alpha Various products
- 32. Detailed Functions of Macrophages Inflammation – Fever, Production of: IL-6, TNF-alpha, IL-1 – act as pyrogen Immunity Selection of lymphocytes to be activated: IL-12 results in Th1 activation IL-4 results in Th2 activation Activation of lymphocytes: Production of IL-1 Processing and presentation of antigen Reorganization of tissues, Secretion of a variety of factors: Degradative enzymes (elastase, hyaluronidase, collagenase) Fibroblast stimulation factors Stimulation of angiogenesis Damage to tissues Hydrolases, Hydrogen peroxide production Complement C3a TNF alpha production Antimicrobial action O2–dependent production of: hydrogen peroxide, superoxide, hydroxyl radical, hypochlorous acid O2-independent production of: acid hydrolases, cationic proteins, lysozyme Anti-tumor activity produced by: Toxic factors Hydrogen peroxide Complement C3a Proteases, Arginase Nitric oxide TNF alpha
- 33. Natural Killer (NK) Cells . • Derived from bone marrow. • Lack most markers for T and B cells (do not have TCR). • Do not undergo thymic maturation. • Express CD56, a specific NK marker. • Express a receptor for Fc portion of IgG, called FcRIII (CD16). • Cytokines (IL-2) promote differentiation into lymphokine – activated killer (LAK) cells.
- 34. NK- Cell Effector Mechanisms. • Mechanism of killing similar to those of Tc cells • Not MHC-restricted. Susceptibility of target cell to killing is inversely proportional to expression of class I MHC (killer inhibitory receptors , KIR) on NK cells recognize class I MHC and prevent killing .
- 35. NK Effector Mechanisms (continued) • IgG-coated target cells recognized by FcRIII (CD16) are killed by antibody- dependent cell-mediated cytotoxicity (ADCC). • Lymphokine-activated killer cells (LAK) kill broader range of cells than do NK cells.
- 36. Regulation of Immune Responses. • Magnitude determined by balance between the extent of lymphocyte activation and tolerance induced by an antigen. • Nature determined by specificities and functional classes of lymphocytes activated. • Regulatory mechanisms may act at : the recognition, activation, or effector phases of an immune response.
- 37. Cytokines Regulate Ig Class Switching • Fc region of antibodies determines effector function in different anatomical locations • Class (isotype) switching produces class or subclass of antibody most effective in host defense • Cytokines acting alone or in combination regulate class switching
- 38. T regulatory cells. • CD4+CD25+ population is generated in the thymus. In addition, CD4+ T regs can be induced from non-regulatory T cells in the periphery. • T regs do not prevent initial T cell activation, they inhibit a sustained response and prevent chronic and potentially damaging responses.
- 39. T regulatory cell development
- 40. T regulatory cell (continued) • T regulatory cells are anergic (non-responsive) in vitro • They do not have characteristics of Th1 or Th2 CD4+ cells • T regulatory cells express Foxp3. • Mutations in Foxp3 cause immune dysregulation (polyendocrinopathy enteropathy, X-linked syndrome). Leads to increased autoimmune and inflammatory disease. • T regs can suppress both the Th1 and Th2 responses
- 41. Possible CD25+CD4+ Treg suppression mechanisms in vivo. • Tregs may act in a cell contact–dependent manner by competing directly for stimulatory ligands on the APC • By competing for essential growth factors such as IL- 2 • Directly transmitting an as-yet uncharacterized negative signal. • Secretion of suppressive cytokines such as IL-10 and TGF-β. • CD25+CD4+ Tregs may act through the APC 1. generation of immunosuppressive metabolites, 2. by perturbing the APC’s presenting capacity. • Such mechanisms are not necessarily mutually exclusive, and more than 1 might operate in tandem.
- 42. Possible mechanisms of T regulatory cell suppression of the immune response