Chapter15 B cell mediated immune response
B cells mediated immune response
Humoral immunity(HI) or antibody mediated immunity:
The total immunological reaction that B cells recognize antigen, then to be activated, proliferate, differentiate into plasma cells and produce Ab.
• B2 cells mediated immune response to TD-Ag• B1 cells mediated immune response to TI-Ag
Contents
Part Immune response of B2 cell to TD-AgⅠ
Part II Rules of humoral immunity
Part Ⅲ Immune response of B1 to cell TI-Ag
Part Immune response of B2 cell to TD-AgⅠPart Immune response of B2 cell to TD-AgⅠ
Characteristics of TD-Ag:• Possess T cell epitope and B cell epitope• Need Th cells participation• Both CMI and HI• Produce several types of antibodies: IgG
• Produce immune memory
• B2 cells recognize TD-Ag activate, proliferate,
differentiate plasma cells produce Ab
1.1. B cells recognize antigenB cells recognize antigen
• BCR directly recognize the conformational determinant, capture Ag and present Ag signal to Th cells
• No APC , no MHC restriction
• Specificity
conformationallinear
2. B cells activation, proliferation 2. B cells activation, proliferation and differentiationand differentiation
(1) B cell activation: dual signals • First signal : antigen signal BCR--conformational determinant on the surfa
ce of Ag Igα/Igβtransduct first signal CD19/CD21/CD81 (co-receptor) binds to C3d o
n Ag• Second signal: co-stimulatory signal The CD40 on B cells binds to CD40L on activ
ated T cells
CD225
(Leu-13)
Endosome
CD40
Immunoglobulinreceptor
MHC II
Antigen
Cytokine receptor
Bcell
B7B7B7B7 CD28
TCRTCRTCRTCRT helpercell
1. Antigen presentation toTh cell
2. B7 expressed
Bcell
3. Th cell is activated
and expresses CD40 ligand,
Cytokines secretedCD40
ligand
Cytokine
Bcell
T helpercell
Bcell
Bcell
Bcell
5. B cell activated
6. B cells proliferate, differentiate, secrete Ig
Interaction between Th cell and B cell
B cells act on Th cells:• B cells present Ag to Th cells• B cells provide B7 for Th cells
Th cells act on B cells:• Activated Th cells provide co-stimulatory
molecule for B cells: CD40L—CD40• Activated Th produce Cks ( IL-4 、 IL-5 、 IL-
6 、 IL-10 、 IL-13 ) which help B cells proliferate and differentiate
(2) B cells proliferate and differentiate------help of Th
• Activated B cells express receptors of cytokines(IL-4R, IL-5R, IL-6R )
• Activated Th2 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
免疫记忆免疫记忆
cytokines
Thymus dependent antigen
CD4 T cells
cytokines
Functions of CK in HI Promote B cell to proliferate and differentiateDetermine the types of Abs produced by isotype switch
Differentiation of B cell in germinal Center
① Some B cells differentiate into plasma cells
② Somatic hypermutation of B cells induces affinity maturation of Ab
③ Some B cells have isotype switch to produce other types of Ig---need help of CKs
④ Production of memory B cells
lymph node
IgM switchIgM switch to IgGto IgG
IgM switch IgM switch to IgAto IgA
3. Effect Stage3. Effect Stage
---the function of Ab ---the function of Ab
1. Neutralization: * neutralize microbial toxins and animal venoms * prevent viruses and bacteria from infecting cells
2. ADCC—NK Antibody-coated target cells can be killed by natural killer cells(NK cell) in antibody-dependent cell-mediated cytotoxicity, that is called ADCC.
3.Opsonization – macrophageFc receptors on phagocytes trigger the uptake of antibody-coated bacteria.As a result, this action enhance phagocytosis of the bacterium.
Complement proteins bind to antibodies.Complement proteins bind to antibodies.
4.Activation of complement Complement can be activated to directly lyse bacteria by the presence of Complement can be activated to directly lyse bacteria by the presence of antibodies bound to the bacteria.antibodies bound to the bacteria.
5. Participate in hypersensitivityIgE 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
Part II Rules of humoral immunityPart II Rules of humoral immunity
1. Primary response
2. Secondary response
• ____________________________________________
• Primary IR Secondary IR• ____________________________________________• latent phase long short• peak concentration low high• maintaining time short long• Ab type mainly IgM mainly IgG• Ab titer low high• affinity low high• ____________________________________________
Significance:
On diagnosis: IgM is a marker for early diagnosis of infectious diseaseOn vaccination : To obtain secondary response by more times of
vaccination
Part III Immune response of B1 cellPart III Immune response of B1 cells tos to TI-Ag TI-Ag
Characteristics of TI-Ag:
• Repeated B cell epitopes• No participation of T cells • Only humoral immunity• Only produce IgM• No immune memory
• TI-1 Ag usually called B cell mitogen • High TI-1 Ag can induce polyclonal B cells proliferation
and differentiation• Low TI-1 Ag only stimulate B cell clone with specific
BCR• Response of B1 cell to TI-1 Ag earlier than that of B2
cell to TD-Ag• No Ig isotype swicth, affinity maturation, and memory
B cells
B1 cells mediated immune response to TI-1 Ag:
• Most TI-2 Ags have highly repeated epitope
• Only stimulate mature B1 cells
• Density of epitope is key to TI-2 Ag to activate B cells
• Help macrophage phagocytose and digest extracellular bacteria under antibody of capsule polysaccharide
B1 cells mediated immune response to TI-2 Ag
SummarySummary
Process of Immune response mediated by B2 cell to TD-Ag
Immune response of B1 to cell TI-Ag
Difference of primary HI and secondary HI
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