B cell maturation and Ab synthesis Flashcards
List the steps of B cell maturation
Pro-B –> Pre-B —> B cell —> Plasma Cell
During which stage of B cell maturation does D-J rearrangement for heavy chain occur
Pro-B cell (early stages of heavy chain production)
During which stage of B cell maturation does V-DJ rearrangement for heavy chain occur?
Pre-B cell
Which stage does initiation of light chain rearrangement occur?
Pre-B cell to B cell. Once light chain is synthesized, you have a B cell
What stage of B cell maturation secrete antibodies?
Plasma cells
Where does differentiation of B-cell occur?
in bone marrow
Pre-B cell turns turns on a gene whose product is?
Surrogate light chain
Accessory molecule (a fake light chain) that binds to cytoplasmic u heavy chain and brings a small amount to the surface
Surrogate light chain
When the surrogate light chain brings a part of the heavy chain to the surface, what two important signals does it give off?
Tells cell to stop undergoing further V-DJ rearrangement and to start rearrangement of light chain
Pre-B cell has what marker?
Cytoplasmic u heavy chain (recall that IgM is the only Ig present in immature B cell)
Antibody synthesis is mediated by rearrangement of ____ to form functional Ig genes
Ig gene segments
First stage of Ab synthesis
Rearrangement of heavy chain segments
Heavy chain segments are made of the following gene segments:
Variable (V)
Diversity (D)
Joining (J)
Constant Region (C)
VDJ rearrangement results in a functional _____
V region
What does the functional V region (VDJ rearrangement) encode?
Heavy chain variable domain of the assembled antibody molecule
After VDJ rearrangement, RNA synthesis of the rearranged ehavy chain gene is initiated and proceeds through which region gene segments?
C region
What is the primary transcript processed into?
mRNA
What is the mRNA then translated into?
IgM, D, G, A, or E, depending on the stage of B cell maturation and class switching
Amount of V heavy chain domains (VH)
and V light chains
100 VH, 35 VL
amount of D heavy chain domains and D light
27 DH, and 0 DL!
Amount of J heavy chain domains and Jlight
6 JH, and 5 JL
What is rearranged in light chain?
V-J
After V-J rearrangement, RNA synthesis of the rarranged light chain gene is initiated and proceeds through the C region gene segments. This primary transcript is processed into what?
mRNA
light chain mRNA is then translated into?
Kappa or lambda light chains
Once the light chain and heavy chain synthesis have occured, an Ig is assembled where?
In B cell and transported to cell surface
When does Ig convert from a membrane anchored form to a secreted form?
Upon differentiation of the B cell into a plasma cell
What enzyme mediates the V-DJ rearrangement?
VDJ recombinase; it can cleave/ligate/correct DNA errors
VDJ recombinases that are lymphoid specific (T cells and B cells)?
RAG1 and RAG2 = recombinase activating genes (need lymphoid specific so it doesn’t occur in…skin or kidney!)
What ensures that you have correct rearrangement order of DJ and then V-DJ?
12-23 spacer rule
What are the 5 molecule basis of Ig Diversity?
- Multiple V region genes
- Recombination of VJ and VDJ gene segments
- Combinatorial association of H and L chains
- Junctional Diversity
- Somatic hypermutation
How many multiple V region in heavy and light chains?
V heavy = 100
V light = 35
How many recombination variations can you have for heavy chain VDJ and light chain VJ gene segments?
VDJ = 16,200 (100V*27D*6J) VJ = 175 (35V * 5J)
How many H and L combinatorial associations?
16,200 *175 = 2.836 x 10^6 different combinations
When the gene segments come together during the rearrangement process but don’t combine faithfully
Junctional diversity
This enzyme is shown during VDJ rearrangements in junctional diversity that adds nucleotides in a non-template driven fashion at DNA break points prior to ligation
terminal deoxynucleotidyl transferase
Junctional sites on heavy and light chains
heavy chain : V and D, D and J
light chain: V and J
When does somatic hypermutation take place?
After B cell engages antigen (antigen dependent)
Antibodies mutate at a higher/lower rate than DNA in rest of genome
Higher rate. Particularly in the DNA coding the variable domains
What are the two main things Somatic hypermutation contribute to?
- affinity maturation
2. upregulates Activation Induced Cytodine Deaminase (AID)
higher affinity antibodies will out-compete the lower affinity antibodies (higher affinity B cell will survive, lower affinity dies)
Affinity maturation
This enzyme introduces mutations into the variable domains of Igs; contributes to converstions of nucleotides from DNA into RNA (by uridine) leading to affinity maturation
AID
When does AID become activated?
When B cell is activated
B cells undergo asymmetric division to form?
Memory B cells and plasma cells
Circle of DNA consisting of everything between the “D3” and “JH4” connection (could be any one of the Ds with the Js in heavy chain)
Circular episome
If you knock out RAG genes, what happens?
Severely compromise immune system
2 antigen independent steps of antigen biosynthesis/modification
- VDJ rearrangement
2. VJ rearrangemet
Antigen dependent steps of antigen production
- class switching
2. somatic hypermutation
