B lymphocytemediate recognition of antigens and the immune response - PowerPoint PPT Presentation

Title: B lymphocytemediate recognition of antigens and the immune response


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B lymphocyte-mediate recognition of antigens and
the immune response

• 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

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Humoral immunity A immune
response mediated by B lymphocyte-secreted
antibodies. Its funtion is to neutralize and
eliminate the antigens which induced the
antibodies.
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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
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• TI-1 antigen also named B cell mitogen
• Contains B cell mitogen and repeated B epitopes
• Can induce immature and mature B cell-mediate
  immune response
• In high concentrations, can induce polyclonal
  B-cell activation
• In lower concentrations, only the BCR-binding
  TI-1 antigens can activate B cells
• Not able to induce Ig class switch, antibody
  affinity maturation and memory B cells

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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
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• TI-2 antigen
• Only contains multitude repeated B-cell epitopes
• Merely induces mature B cell-mediated immune
  response
• Unresponses or hyporesponsive to infantile B
  cells
• Activates the B-1 cells

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TI-2 antigen alone activates B cells to secrete
antibodies
cell
B cell-mediate recognition and immune response to
TI-2 antigens
Plasma cell
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• TI antigen mainly activates CD45 B1 cells
• The produced antibodies are mainly IgM
• No MHC-restriction, without APC and Th cell help
• Can not induce antibody class switch, affinity
  maturation and memory B cells

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(?)B cell-mediate recognition to TD antigens

• BCR binds to antigen specifically and transfer
  the antigen stimulatory signal into B cells
• BCR specific binding to the antigen and intake it
  through internalization, then the antigen was
  degradated into peptides and the peptide-MHC-II
  molecule complex was formed, which can be
  recognized by antigen specific Th cells

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Comparison of TD antigen with TI-1 and TI-2
antigens
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?. Activation of B Cells
1)The specific antigenic recognition signal of B
cell activation (first signal)
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B cell coreceptor complex
The first signal of B cell activation
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2)Costimulatory signal of B cell activation
(second signal)
With the help of T cells
1.The activation of naïve Th cell
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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.
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?Direct contact T cells express
CD40L,LFA-1,CD28 , et al. CD40/CD40L,ICAM-1/LFA-1
,B7/CD28 The most important molecule is
CD40L(CD154)
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B cell
Th cell
antigen
Signal 1
Th activation
Presentation of antigen
Signal 2
Signal 2
Signal 1
B activation
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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

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The function of cytokines
IL-2, IFN-? secreted by Th1 cells IL-4?IL-5?IL-6
secreted by Th2 cells
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TD antigen
B cell
Th cell
cytokines
B cell
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?. The signal transduction of B cell activation
(?)the antigen recognition structure of B cells
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Signal transduction in B cells
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4. differentiation and maturation of B cells in
the germinal center

• FDC, B cell interaction ---B cell uptake
  antigens.
• Antigen uptaken, process and presentation by B
  cells.
• T, B cell interaction---Th cell activation.
• CD40L upregulation and cytokine secretion in
  activated Th cells---further differentiation and
  maturation of B cells.

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B cell activation and GC formation
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(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.
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(2) somatic hypermutation and affinity
maturation
Ig B cells proliferate rapidly, and their
already rearranged receptor genes undergo further
diversification. Some further diversifided Ig B
cells acquir more affinitive BCR.
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B cell differentiation and maturation in germinal
center
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(3) immunoglobulin class switch
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(4) destiny of maturated GC B cells

• plasma cell, PC
• memory B cell

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(6) Humoral immune response

• Primary immune response
• Secondly immune response or
• anamnestic response

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Primary immune response ?lag phase ?log
phase ?steady-state phase ?decline phase
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Antigen
Steady-state phase
Lag phase
Antibody titer
Log phase
Decline pahse
Time
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• Secondly immune response or anamnestic response
• Short lag phase
• longer steady-state phase
• lower dose of antigen needed
• mainly IgG
• highly avidity

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Master the general rule of B cell mediated immune
response angainst TD-Ag. Master similarities and
differences between TI-Ag and TD-Ag inducing B
cell immune response. Understand mucosal immune
response. Understand mature , somatic
hypermutation and affinity maturation and class
switch of B cell.