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Humoral Immunity
- 1. Ephantus Njagi Mechanisms ofHumoral Immunity
- 2. Background Mechanisms ofhumoral immunity are accomplished after interaction of: B cells Antibody production antigen binding
- 3. Interaction of antigenwith B cells Each antibody binds to a specific antigen similar to a lock and key through: Noncovalent bonds or Intermolecular forces. Hydrogen bonds Electrostatic bonds Van derWaal forces Hydrophobic bonds An immune complex is formed from the integral binding of an antibody to a soluble antigen. The bound antigen acting as a specific epitope, bound to an antibody is referred to as a singular immune complex.
- 4. B-cell Activation andDifferentiation
- 5. Clonal expansion andDifferentiation
- 6. B cells mediatedimmune response Humoral immunity(HI) or antibody mediated immunity: The total immunological reaction that B cells recognize antigen, then activate, proliferate, differentiate into plasma cells and produce Ab. B2 cells mediated immune response toTD-Ag B1 cells mediated immune response toTI-Ag
- 7. PartⅠ: Immune responseof B2 cell to TD-Ag Characteristics ofTD-Ag: PossessT cell epitope and B cell epitope NeedTh cells participation Both CMI and HI Produce several types of antibodies: IgG Produce immune memory
- 8. 1. B cellsrecognize antigen BCR directly recognize the conformational determinant, capture Ag and present Ag signal to Th cells No APC , no MHC restriction Specificity
- 9.
- 10. Clonal Selection B-cells Antibodyon Surface Antigens Only B-cells that bind antigen are selected
- 11. Clonal Expansion B-cells Antibodyon Surface Proliferation of selected B-cell
- 12. Somatic Mutation B-cells Antibodyon Surface Improved Antibody Binding By Genetic Rearrangement Somatic Mutation
- 13. 2. B cellsactivation, proliferation and differentiation (1) B cell activation: double signals First signal : antigen signal BCR--conformational determinant on the surface of Ag Igα/Igβtransduct first signal CD19/CD21 (co-receptor) binds to C3d on Ag Second signal: co-stimulatory signal The CD40 on B cells binds to CD40L on activatedT cells
- 14. CD40 Immunoglobulin receptor MHC II Antigen Cytokine receptor B cell B7 B7 CD28 TCR TCR Thelper cell 1. Antigen presentation to Th cell 2. B7 expressed B cell 3. Th cell is activated and expresses CD40 ligand, Cytokines secreted CD40 ligand Cytokine B cell T helper cell B cell B cell B cell 5. B cell activated 6. B cells proliferate, differentiate, secrete Ig
- 15. Interaction between Thcell and B cell B cells act onT helper cells: B cells present Ag toTh cells B cells provide B7 forTh cells T helper cells act on B cells: ActivatedTh cells provide co-stimulatory molecule for B cells: CD40L-D40 ActivatedTh produce Cytokines to help B cells proliferate and differentiate Activated B cells express receptors of cytokines ActivatedTh2 secrete cytokines IL-4, IL-5, IL-6 to enhance proliferation and differentiation of B cells B cells differentiate into plasma cells (antibody forming cells)- produce Ab, some activated B cells become memory B cells
- 16. Interactions between Bcell and Th cell B cell activation B cell Th cell Ag processing Th cell activation
- 17. Cytokines affect proliferationand Class switch of B cells
- 20. 3. Stage ofeffect----the function of Ab 1. Neutralization-Ab covers up sites on toxic molecule/virus. 2. Opsonization-Ab-mediated phagocytosis. 3. Complement fixation-cascade reacts to ag-ab complexes. 4. Agglutination/precipitation-Cross-link ags into complexes-aids phagocytosis. 5. Immobilization-Abs bind to flagella etc. & prevent escape macrophage death. 6. ADCC-NK, macrophage 7. Participate in hypersensitivity-I,II,III
- 21. 1. Neutralization: * toneutralize microbial toxins and animal venoms * to prevent viruses and bacteria from infecting cells
- 22. 2. ADCC—NK Antibody-coated targetcells can be killed by natural killer cells(NK cell) in antibody-dependent cell-mediated cytotoxicity, that is called ADCC.
- 23. 3.Opsonization – macrophage Fcreceptors on phagocytes trigger the uptake of antibody-coated bacteria. As a result, this action enhance phagocytosis of the bacterium.
- 24. Complement proteins bindto antibodies. 4.Activation of complement Complement can be activated to directly lyse bacteria by the presence of antibodies bound to the bacteria.
- 25. 5. Participate inhypersensitivity IgE binds to high-affinity Fc receptors on mast cells and basophils, and leads to the rapid release of granules containing inflammatory mediators into surrounding tissue, cause hypersensitivity
- 30. Primary and secondaryantibody responses to protein antigens differ qualitatively and quantitatively