Transcript PowerPoint 演示文稿 - Shandong University

Chapter 14
B Lymphocytes
Contents
B cell receptor and B cell complex
B cell accessory molecules
B cell subpopulations
Functions of B cells
B cell maturation
BCR diversity and
TCR diversity
I. B cell antigen receptor and B
cell receptor complex
BCR
BCR complex
Function: Recognize antigen
1. B cell receptor----BCR
• Membrane immunoglobulin
(mIg) on B cells: mIgM,
mIgD
• Recognize and bind
antigen specifically
2. BCR complex
• BCR and Ig - Ig  (heterodimer)
Ig (CD79a) , Ig (CD79b)
• Participate in BCR formation
• ITAM------bind to tyrosine kinase
• Transmit activating signal
II. Accessory membrane molecules
on B cells
1.
CD19, CD21(CR2), CD81(TAPA-1)
----B cell co-receptor complex
 CD21(CR2): receptor of C3dg,C3d and iC3b
----Enhance the binding of BCR and antigen
----Pass activating signal to CD19
----EB virus receptor
 CD19: Transmit activating signal into B cell
2. CD40----co-stimulatory receptor
• CD40 on B cell binds to CD40L on activated T cell
• Transmit an important co-stimulatory
signal to B cells
• Upregulate expression of B7 on B cells
• Participate in class switching of antibody
3. Co-stimulatory molecule: B7
• B7-1 (CD80) and B7-2 (CD86)
• Expressed on B cells or other APC
• B7-CD28: activation signal
• B7-CTLA-4: inhibitory signal
4. MHC molecules
• Class Ⅰ,Ⅱ MHC molecules
5. Mitogen receptor
• SPA, LPS
• PWM
6. Cytokine receptor
• IL-4R, IL-5R, IL-6R
7.Fc receptor (CD32---FcRII-b)
------Related to immunological regulation
III. B cell subpopulations
According to expression of CD5 or not
B1 cell (CD5+)
B2 cell (CD5-)
Comparison of B1 and B2 cells
B1
B2
Development
early
late
BCR
mIgM
mIgM and mIgD
CD5
+
Reproduction self-renewing
from pre-B cell in BM
Recognized Ag TI-Ag and auto-Ag
TD-Ag
Ab type
IgM >IgG
IgG >IgM
Ab avidity
low
high
Second IR
+
Function
innate immunity
adaptive immunity
IV. Functions of B cells
Produce the antibody----HI
Present antigen----APC
Participate in immunological regulation: secrete
various cytokines, FcRII-b
The comparison of main membrane
molecules between T and B cells
T lymphocyte
B lymphocyte
functions
Antigen receptor
TCR
BCR
Ag receptor
complex
CD3 and ξ链
Igαand Igβ
Transmit first signal
Co-receptor
CD4,CD8
CD19-CD21
complex
Help to bind Ag，
Transmit first signal
Co-stimulatory
receptor
CD28
CD40
Co-stimulatory
molecules
CD40L
MHC I
expression
expression
Antigen processing
MHC II
Activated
expression
expression
Antigen processing
Bind to Ag,
First signal
Second signal,
Transmit second signal
B7(CD80/CD86) Offer second signal
SectionⅡ Development and
differentiation of B cells
Differentiation of B cells in Bone marrow
Differentiation of B cells in peripheral
lymphoid tissue (B cell mediate immune
response, HI)
μ
1. Differentiation of B cells in
Bone marrow----Ag independent
•
•
•
•
•
•
•
Hematopoietic stem cells
Lymphoid progenitor
Pro-B cells( chain rearrangement)
Pre-B cell( chain + surrogate light chain )
Immature B(mIgM,  chain +κchain orλchain)
Mature B(mIgM, mIgD)
Functional B repertoire
Negative selection of B cells in
bone marrow
2. Differentiation of B cells in peripheral
lymphoid tissue----Ag dependant
• Virgin B/naïve B cell
most die
• Plasma cell
Ab
• Memory B cell
secondary
immune response
3. Events in the differentiation of B cells:
Gene rearrangement of Ig
Negative selection
Immature B cells :
mIgM--self antigen
mIgM -- self antigen
apoptosis or anergy
surviving to develop
mature B cells
Questions?
Why can TCR or BCR recognize so many
Ag in nature?
Why does IgM produce earlier than others?
How does Ig produce BCR and Ab?
How can B produce different type of Igs?
---------------?
PartⅢ BCR diversity and TCR diversity
BCR diversity
TCR diversity
SectionⅠ BCR diversity
 Gene structure of Ig
 Gene rearrangement of Ig
 Characteristics of Ig gene expression
 Mechanism of Ig diversity
1. Germ line gene structure of Ig (human)
H chain:14 chromosome
V region encoding genes:
VH (variable gene segments) – 65
DH (diversity gene segments) – 27
JH (joining gene segments) – 6
Leader sequence—signal peptide
C region encoding genes:
CH (constant gene segments): Cμ, Cδ, Cγ et al. (11)
L chain(--2 chromosome, --22 chromosome)
V region encoding genes:
– 40, 5
-- V, J – 30, 4
 --V, J
Leader sequence—signal peptide
C region encoding genes:
C (1); C(4)
In heavy chains, the V, D and J
segments encode the variable
domain while the C segment
encodes the constant domain.
In light chains, the V and J segments
encode the variable domain while
the C segment encodes the constant
domain.
(a)  Chain (22 chromosome))
V
JC JC JC JC
(2 chromosome)
2. Gene rearrangement of Ig
V-D-J rearrangement of H chain
pro-B cells: D-J
V-DJ
VDJ
DNA
transcription
pre-B cells: VDJCμ splicing VDJ- Cμ
RNA
mRNA
V-J rearrangement of L chain
pre-B cells: V  -J 
VJ
immature B cells: V  J  C
mRNA
DNA
V  J  -C
RNA
C C C3 C 1 C1 C2 C4 C C2
C C C3 C1 C1 C2 C4 C C2
C C C3 C1 C1 C2 C4 C C2
C
C
C
C

The expression of BCR
Intranuclear:
DNA rearrangement:
------- V region encoding gene (VDJ or VJ)
Transcription and splicing
-------leader sequence + V region encoding gene + C
region encoding gene (L gene-V gene –C gene)
Extranuclear:
Translation -------- nascent peptide L-V-C
Endoplasmic reticulum:
assembly--------H chain and L chain (IgM or IgD)
transportation------BCR (membrane Ig, mIg)
3. Characteristics of Ig gene expression
① recombination enzyme:
RAG (recombination activating gene)
TdT (terminal deoxynucleotidyl transferase)
other DNA enzymes
② Allelic exclusion and isotype exclusion
Allelic exclusion:
only one of the two alleles in homologous
chromosomes can be expressed.
Isotype exclusion:
only one of the two types of light chain genes can
be expressed(:=65:35).
Kuby Figure 5-10
Read Kuby pages 115-117: Allelic Exclusion Ensures a Single Antigenic Specificity
③ Isotype switching ( class switching )
Ag
activated B cells proliferate
VDJ is switched to recombine with another C
region encoding gene
IgM
IgD, IgG, IgA, IgE
Switching region
④ Membrane type (BCR) and Secretory type Ig (Ab)
4. Mechanism of Ig diversity
① Combinatorial diversity
human Ig:
65VH×27DH ×6JH=10530V
40V ×5J =200V
30V ×4J  =120V
C C C3 C 1 C1 C2 C4 C C2
C C C3 C1 C1 C2 C4 C C2
C C C3 C1 C1 C2 C4 C C2
C
C
C
C

② Junctional diversity
 CDR3 lies in V-DJ or D-J junctions
 Lose or insert of several nucleotides will
increase the diversity of CDR3.
 N-nucleotides insert by TdT without template
 There is no N-nucleotides insert in L chain
③ Somatic hypermutation
Ag
activated B cells proliferate
gene mutation in V region encoding genes
affinity maturation
mature B cells which finished V gene rearrangement
SectionⅡ Gene structure and
rearrangement of TCR
1. Gene structure of TCRαβ
α chain (14 chromosome): V, J, C
β chain (7 chromosome): V, D, J, C
(14 chromosome)
(7 chromosome)
2. Gene rearrangement of TCRαβ
TCR β chain rearrange first
Inactivate δ gene within α gene
3. Gene structure of TCRγδ
γ chain (7 chromosome): V, J, C
δ chain (14 chromosome): V, D, J, C
4. Gene rearrangement of TCR γδ
No junctional diversity in TCR γδ
(7 chromosome)
(14 chromosome)
5. Characteristics of TCR gene expression
•
Without somatic hypermutation
•
•
More N- nucleotides insert than BCR
More valid rearrangement in V region of TCR
BCR: 1014
TCR: 1016
Comparison of BCR and TCR
functional genes
•
NO. of chain Chromosome V
D
J
C
• ----------------------------------------------------------------------• BCR
H
14
65 27 6
11
•

2
40
5
1
•

22
30
4
4
• TCR

14
70-80
61
1
•

7
52
2 13 2
•

7
12
5
2
•

14
4
3 3
1
What you should know of this lecture
Definition of BCR/BCR complex
Major surface membrane molecules on B
cells (comparison)
Comparison of B1 cell and B2 cell
Functions of B cells
B cell maturation