Transcript Features of B lymphocyte development

Lymphocyte Development & Generation
of Lymphocyte Antigen Receptors
• Pin Ling (凌 斌), Ph.D.
ext 5632; [email protected]
• References:
1. Abbas, A, K. et.al, Cellular and
Molecular Immunology (6th ed., 2007),
Chapter 8
Questions
What is the Bare Lymphocyte Syndrome?
 An immunodeficiency disease
 Lacking Class-II MHC expression
 Mutations in transcriptional factors regulating Class II
expression, ex. CIITA
What is the advantage of MHC
Polymorphism? Is that good if MHC is
as diverse as Ig or TCR?
 MHC polymorphism may provide a broader protective
immunity in a population during pathogen infection .
Outline
• Overview of Lymphocyte Development
• Generation of Diversity in Lymphocyte
Ag receptors
• B & T Lymphocyte Development
• Summary & Question
Key Concepts in lymphocyte development
1. Lymphocyte development-A process of differentiation
of lymphoid progenitor cells into mature lymphocytes (T
& B).
2. Rearrangement and expression of Ag receptor genes
are associated with lymphocyte development.
3. Selection events are involved in preserving cells w/
correct Ag receptors and eliminating dangerous cells
w/ self-recognition Ag receptor
4. Proliferation in the early lymphocyte development is
stimulated by IL-7.
Stages of lymphocyte development-I
Checkpoints in lymphocyte development
Selections in
lymphocyte
development
Pluripotent HSCs
=> lymphocyte
lineages
Outline
• Overview of Lymphocyte Development
• Generation of Diversity in
Lymphocyte Ag receptors
• B & T Lymphocyte Development
• Summary & Question
Key Concepts in Diversity of
lymphocyte Ag receptors
1. The germline organizations of Ig & TCR are similar.
a. Multiple (V)ariable, (D)iversity, & (J)oining gene segments.
b. These gene segments are spatially separated on the
chromosomes
2. During lymphocyte development, gene rearrangement of
Ag receptor genes occurs:
a. Combinatorial diversity
- Non-homologous DNA recombination (VDJ recombination)
- Lymphoid-specific enzymes- RAG1 & RAG2
Other factors-DNA-PK, TdT, Ku, DNA ligase IV…
b. Junctional diversity
- Addition or removal of nucleotides among V (D)J joints
-The largest contribution to diversity of Ag receptors
In 1970s, Scientists thought
105 genes in human body => Antibodies over
1010 ?
=> Limited gene segments
 Hybrid-DNA nature (Recombination)
 Diverse Ab products
Germline organization of Human Ig loci
D segment
in H chain
Germline organization of Human TCR loci
D segment
in b chain
Domains of Ig & TCR proteins
HV3 or CDR3
Generation of Diversity in Ag
receptor genes
V(D)J
Recombination-I
1. Recombination Signal
Sequence (RSS):
Heptamer & Nonamer
=> separated by 12or 23- spacers
=> Recognized by
Recombinase
2. Deletion-VJ exons
have the same
orientation
3. Inversion – VJ have
the different
orientation
V(D)J Recombination-II
V(D)J Recombination III –
Junctional Diversity
Junctional diversity=> the greatest variability
at HV3 (CDR3)
Generation of Diversity in Ig or TCR
Generation of Diversity in Ig or TCR
Overview of Ig gene rearrangement
Outline
• Overview of Lymphocyte Development
• Generation of Diversity in Lymphocyte
Ag receptors
• B & T Lymphocyte Development
• Summary & Question
Pluripotent HSCs
=> lymphocyte
lineages II
1. Regulated by
transcriptional factors
2. Notch-1 & GATA3 => T
EBF, E2A & Pax-5 => B
Features of B lymphocyte development
1. Maturation of B Lymphocytes development
- Rearrangement & expression of Ig gene in a precise order
- Selection & proliferation of pre-B cells via pre-Ag receptor
2. Selection of the mature B cell repertoire
- Self Ag => Affect the strength of the BCR signal
- Immature B cells => self Ag/high avidity => Receptor editing =>
Additional L chain recombination => Not Self-reactive
=> Fail to receptor editing => Apoptosis
3. During this maturation, B cell lineage cells go through
distinct stages => A specific Ig gene expression
=> Distinct surface markers
4. At Pre-B cell stage, H chain recombination occurs first and
associates w/ Surrogate light chains (l5 & VpreB).
- l5 & VpreB are similar to k & l light chains but invariant
- form pre-B cell receptor => Development
Stages of B lymphocyte development-I
Stages of B lymphocyte development-II
Pre-B cell & Pre-T cell receptors
Stages of B lymphocyte development-III
Receptor Editing–2nd Chance
Features of T lymphocyte development
1. Maturation of T Lymphocytes development
- Sequential Rearrangement & expression of TCR genes
- Selection & proliferation of T cell repertoire
2. Selection of the mature T cell repertoire occurs in Thymus
- Positive selection => Self MHC-restricted
- Negative Selection => Self Ag-MHC/high avidity =>
Apoptosis => Central Tolerance
3. CD4 & CD8 are surface markers for differentiation of
Thymocytes (immature T cells).
Stages of T lymphocyte development-I
Maturation of T lymphocytes in Thymus
CD4 & CD8 expression on Thymocytes
Selection of T lymphocytes in Thymus
TCR transgenic
mouse model
=> T cell
selection
Outline
• Overview of Lymphocyte Development
• Generation of Diversity in Lymphocyte
Ag receptors
• B & T Lymphocyte Development
• Summary & Question
SUMMARY
1. Rearrangement and expression of Ag receptor genes
regulate B & T lymphocyte development.
2. Selection events are involved in preserving cells w/
correct Ag receptors and eliminating dangerous cells
w/ self-recognition Ag receptor
3. Gene rearrangement of Ag receptor genes occurs during
lymphocyte development.
- The basic mechanism is common to both B & T cells
- Generate the Combinatorial diversity by randomly
combining different V(D)J gene segments
- Generate the Junctional diversity by filling the gap
betweenjointed gene segments
Question
What is happened to the immune
system if RAG1 & RAG2 are mutated?