B lymphocyte-mediate recognition of antigens and the immune response. Contents. B cell-mediate immune response to T-dependent antigen B cell-mediate immune response to T-independent antigen The general rule of humoral immune response. Humoral immunity:
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B lymphocyte-mediate recognition of antigens and the immune response
A immune response mediated by B lymphocyte-secreted antibodies. Its funtion is to neutralize and eliminate the antigens which induced the antibodies.
B cell-mediate recognition to antigens
B cell-mediate recognition to TI antigens
TI-antigen: T-independent antigen
This type of antigen can activate B cells without the T cell help,
and most of them are bacterial polysaccharides and lipopolysaccharide.
1. TI-1 aitigen
2. TI-2 antigen
TI-1 antigen in high concentrations
B-cell mediate recognition and immune response to TI-1 antigens
polyclonal B-cell activation
non-specific antibody response
TI-1 antigen in lower concentrations
Specific antibody response to TI-1 antigen
TI-2 antigen alone activates B cells to secrete antibodies
B cell-mediate recognition and immune response to TI-2 antigens
（二）B cell-mediate recognition to TD antigens
Comparison of TD antigen with TI-1 and TI-2 antigens
二. Activation of B Cells
1）The specific antigenic recognition signal of B cell activation (first signal)
B cell coreceptor complex
The first signal of B cell activation
2）Costimulatory signal of B cell activation (second signal)
With the help of T cells
1.The activation of naïve Th cell
2. The combination of Th cell and specific B cell
TCR presented on Th cells specifically recognizes and binds antigenic peptide-MHC-II complex displayed on B cell surface
The interaction of many adhesion molecular pairs makes the binding tighter.
T cells express CD40L，LFA-1，CD28, et al.
The most important molecule is CD40L(CD154)
Presentation of antigen
3. The activation of specific B cells
Th cells can be induced to express many membranous molecules, for instance CD40L
The dark zone formation of the germinal center in lymph follicles
The clonal proliferation of B cells
B cells are differentiated to the cells in the germinal center
The formation of memory B cells
The function of cytokines
IL-2, IFN- secreted by Th1 cells
IL-4、IL-5、IL-6 secreted by Th2 cells
三. The signal transduction of B cell activation
（一）the antigen recognition structure of B cells
Signal transduction in B cells
4. differentiation and maturation of B cells in the germinal center
Blast proliferated B cells:
mantle zone formation
Non-proliferated B cells:
B cell activation and GC formation
(1) receptor editing
Further immunoglobulin gene rearrangement in seconary lymph organs---some potentially self-reactive B cells may be rescued.
Otherwise, self-reactive B cells undergo apoptosis or anergy.
(2) somatic hypermutation and
Ig+ B cells proliferate rapidly, and their already rearranged receptor genes undergo further diversification.
Some further diversifided Ig+ B cells acquir more affinitive BCR.
B cell maturation, migration and GC formation
B cell proliferation
antigen recognition and affinity maturation
no antigen loading B cells undergoing cell death
generation of plasma or memory B cells
B cell differentiation and maturation in germinal center
(3) immunoglobulin class switch
(4) destiny of maturated GC B cells
(6) Humoral immune response
Primary immune response