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B cell subsets and development
Fetus liver : B1 B
Bone Marrow :
HSC proB preB imB mB
spleen : NF B FP FO B
MZ B
Antigen-independent development of B cells
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three major naive peripheral B-cell populations
B cell
Immunol Rev 2004; 197:206
High-affinity IgG
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INSTITUTE FOR IMMUNOBIOLOGY
B cell and B cell-mediated
humoral immune response
Part II
Department of ImmunologyFudan University
Wei Xu, Ph.D021-54237749
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Overview of the humoral immune response against bacterial
B cells plasma cells
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Significance of humoral immunity
eliminate extracellular bacterium and toxin
eliminate extracellular virus
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B cells and humoral immune response
1. Recognition of the specific Ag2. Activation, proliferation, differentiati
on2. Germinal center: later event3. General feature of Ab response
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highly repetitious molecules, bacterial flagellinbacterial cell-wall polysaccharides with repeating units.
thymus-dependent (TD) antigens
B response to TD Ag requires direct contact with Th cells,
thymus-independent (TI) antigens
TI- 1 Ag
TI-2 Ag
bacterial cell-wall components, lipopolysaccharide (LPS),
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Recognition of TD Ag
Directly recognize Ag
(B cell epitope)
No MHC involvement
surfaced displayed B cell-epitopes
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Ab (BCR) binds the B-cell epitope directly,
TCR binds with a self-MHC-T-cell-epitope complex
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B cell activation
B cell epitope
BCR-Ig/Ig -coreceptor complex
B cell epitope
BCR
Iga/b
Signal
+
Ag-C3d
CR2
CD19
Signal
+
+++
( CD21-CD19-CD81 ) coreceptor
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B cells and humoral immune response
1. Recognition of the specific Ag2. Activation, proliferation, differentiati
on2. Germinal center: later event3. General feature of Ab response
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1) activation1) activation
A. 2-signal activation model
B. the help from Th cell
2) Signal transduction
3) Proliferation and differentiation
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the 2-signal rule the 2-signal rule signal 1 : BCR - B cell epitope
signal 2 : CD40 - CD40 L
B Th
Co-sti mol
CD40L
surviveB7
survive
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B cell activation requires 2 signals
Signal 3: IL-4
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Signal 1 From antigen
BCR serves 2 roles:
1. Ag-induced clustering of BCRs delivers signals that initiate the activation process.
2. BCR internalize the Ag into endosome, process and present on surface for T recognition
Receptor-mediated Ag endocytosis
T cell epitope-MHC II presentationB cell epitope
Recognition of
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Signal 2
Signal 1
From antigen
From ThSignal 3From Th
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Antigen crosslinks mIg(BCR), generating signal 1, which leads to increased expression of class II MHC and costimulatory B7.
Antigen–BCR complexes are internalized by receptor-mediated endocytosis and degraded to peptides, which are bound by class II MHC and presented as peptide–MHC complexes.
Th cell recognizes Ag–class II MHC and B7-CD28 co-stimulation on B-cell membrane which activates TH cell.
Th cell begins to express CD40L.
Interaction of CD40 and CD40L provides signal 2.
Th cell release large quantities of cytokines(IL-4) signal 3 to support the progression of the B cell replication and differentiation.
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Signal 3
Th-secreting cytokines
Regulate B cell differentiation
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B cells and humoral immune response
1. Recognition of the specific Ag
2. Activation, proliferation, differentiation
1) 2-signal activation
2) signal transduction
2. Germinal center: later event
3. General feature of Ab response
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PTK Src family
immunoreceptor tyrosine-based activation motif (ITAM)
Tyrosine kinase phosphorylation cascade
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a genetically determined immunodeficiency disease inability to synthesize all classes of antibody. discovered in 1952 by O. C. Bruton.
Case:a young boy who had mumps 3 times and experienced 19 different episodes of serious bacterial infections during 4 years.Do not raise Abs to any vaccines.
Bruton’s disease
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globulin
globulin
globulin
1937 , Tiselius use Electrophoresis to analyze the serum proteinsWhich comprised of 5 components :albumin 、 1 、 2 、、 globulin
Antibody , IgG
albumin
Serum of un-immunized personElectrophoresis
cathode
anode
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Pathogenesis: failures in B-cell development.
inhibition pro–B to pre–B-cell transition
In 1990s, the gene was cloned which encodes Bruton’s tyrosine kinase (Btk).
Btk play important roles in B-cell signaling vital to the function of mature B cells
Absence of Btk results in the failure of B activation and Ab generation
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B cells and humoral immune response
1. Recognition of the specific Ag
2. Activation, proliferation, differentiation
1) 2-signal activation
2) signal transduction
3) proliferation
2. Germinal center: later event
3. General feature of Ab response
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Early events :follicle ( B ) -paracortex ( T ) border,
B activation and T-B activation
Small amounts of Ab production
Late events :At the germinal center
Presence of Ag and Th
Affinity maturation
Ig class switch (IgM IgG)
Memory B
Early and late event in Ab response to TD antigen
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( T cell )
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Affinity maturation
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1 、 somatic hypermutation
2 、 affinity maturation
3 、 Ig class switch
Ag Th
late event in Ab response to TD antigen in LN
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Dark zone
Light zone
( mantle zone )
Un-activated lymphocytes
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Follicular DC (FDC)
No MHC II
Bind with Ag-Ab ( IC ) by FcR , maintain Ag for long
Provide persistent Ag signal for B cells
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In presence of Ag , by Th’s co-stimulation
Point Mutation of CDR in the Ig V region
Affinity-enhanced BCR(B cell) is selected
affinity maturation
1 、 somatic hypermutation
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2 、 affinity maturation
Result of somatic hypermutation of B cell
B cells with high affinity would survive
Affinity enhancement
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cytokine determined
occur in single B cell
during RNA transcription
ligation of various C gene
the V region of Ig remains, the C region changed
3 、 Ig class (isotype) switch
In response to CD40-CD40L signal and IL-4 from Th cell, the activated B cells undergo the process of heavy chain isotype (class) switching leading to production of Abs with different class of heavy chain.
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Without Th With Th’ help
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Th cell-secreting cytokines determines the Ig class switch
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CD40L signal 、 IL-4 from ThNo Th
The V gene would recombine with a downstream C region gene and the other DNA deleted
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IgM IgG
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1 、 somatic hypermutation
2 、 affinity maturation
3 、 Ig class switch (Th’s help)
Ag Th
late event in Ab response to TD antigen in BM
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5) Fate of the activated B cell
plasma cellplasma cell ,, PCPC
move to BM? Secret high level of Abs move to BM? Secret high level of Abs
memory B cellmemory B cell
maintain in BM? Never die? maintain in BM? Never die?
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follicular B plasma cells
short-lived form a germinal centre plasma cells
1 . plasma cell
follicle
long-lived plasma cell Bone Marrow
marginal-zone B plasma cells
Bm
Early stage
Th
later
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Formation of plasma cells
Nat Rev Immunol 2005; 5:232
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plasma cells
crucial survival signals (BM)
BAFF- BCMAIL-6- IL-6R
Long-lived plasma cells in the bone marrow
内皮细胞选择素血管细胞黏附分子
retention of plasma cells in BM
somatic mutationclass-switch
CXCR4
B-cell-activating factor
survival signals
BCMA : receptor B-cellmaturation antigen
Germinal Center
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B cell response to B cell response to TI antigenTI antigen
CD5 + B1
Low-affinity IgM
No help from Th
No class switch (no IgG)
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Signal 1 : Ag
Signal 2 : mitogen
Mitogen receptor
Polyclonal strong B activation
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Mitogen receptor
BCR
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Signal 1 : cross-linking of lots of BCR
By polymeric saccharide
B cell response to B cell response to TI-2 antigenTI-2 antigen
Repetitive units
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B cells and humoral immune response
1. Recognition of the specific Ag
2. Activation, proliferation, differentiation
2. Germinal center: later event
3. General feature of Ab response
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The general feature of humoral immunity
primary response
Mostly IgM with low affinity , IgG
secondary response
Mostly IgG with high affinity and high level
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primary immune response
① lag phase: long
5 - 10 days
② log phase
③ plateu phase
short
④ decline phase
quickly
Mostly IgM, later IgG, low level and affinity
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secondary immune response
① long
Lag phase: short, 1-3 days , quickly to the top
② strong
The Ab level is 10 times more than that of the primary response
③ most IgG
enhanced affinity
mB act as APC , with high mB7 , and high-affinity BCR, small amounts of Ag can stimulate mB
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5-10 days 1-3 days
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4 、受体修正 (receptor revision)
生发中心内 识别自身抗原的 B 细胞发生 Ig V(D)J 基因的二次重排,使 BCR 被修正为针对非自身抗原。清除自身反应性 B 细胞使针对外来抗原的 BCR 具有更广泛的多样性。
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Where do Th and B cell encounter ?follicle ( B ) -paracortex ( T ) boundary
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( T cell )
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Ag 特异性 T (蓝色)向滤泡边缘移动
Ag 特异性 B (蓝色)向滤泡边缘移动
Ag 特异性 T (棕色)
Ag 特异性 B (蓝色)
在滤泡边缘相遇
滤泡区: B
T
副皮质区: T
B
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