Development of B cells Flashcards
1
Q
gene rearrangement
A
- leads to many different variable regions
- light chains have V and J regions that are randomly chosen
- heavy chains have V,D, and J regions that are also randomly chosen
- recombination is caused by RAG proteins and recombination in signal sequences
- can combine light and heavy chains
- regions of true randomness exist as well
2
Q
germ line
A
- constant regions not next to variable regions
- RNA was cloned from myeloma cell
- cDNA was made
- southern blot of germ line and non-immunologic tissue showed different configurations for Ig gene material compared to the myeloma
- as B cells develop their Ig material is changed in a predictable sequence
- clinically relevant because can help define if leukemia or what type
3
Q
DNA seq
A
- sequence light chain DNA
- the variable region at the site nearest the constant region consisted of a small gene segment- J region
- did not change its relative position in the genome in IgM and D producing B cells compared to the rest of the body but it did change in all other Ig producing B cells
- rearrangment
- heavy chain sequence revealed D region with different configuration in B cells compared to germ line
- remainder of variable region coded b V region, which is rather far from J and D segments
4
Q
kappa genes
A
- V-31-36
- D 0
- J 5
- C 1
5
Q
lambda genes
A
- V-29-33
- D 0
- J 4-5
- C 4-5
6
Q
heave chain genes
A
- V-38-46
- D-23
- J-6
- C-9
7
Q
DNA splicing
A
- rearranges DNA to make genes for Ig molecules
- not RNA
8
Q
V, D, and J combination
A
- RAG 1 and RAG2 recognize signal sequences that determine which segments can be joined together
- joining is imprecise and there is a special mechanism to increase diversity at CDR3 site
- joining of V to J light chains can involve 4 different nt codons to create in frame gene sequence for a variable light chain
- joining of D to J and V-D in heavy chain gene formation can involve multiple reading frames, as most Ds can be read in all three reading frames
- VJ in light chains
- VDJ in heavy chains
- in heavy- D+J first then add V
9
Q
P regions
A
- novel genetic sequence
- replace germ line sequence
- found in all joining junctions
- add a bit of randomness
10
Q
N regions
A
-added by TdT (only in developing B cells in the pro B stages after birth)
-add random nt to VD and DJ joints
-unpaired removed, synthesis/ligase forms joint
-therefore not in light chains
-add randomness
junctional diversity adds even more then VDJ combos
11
Q
checkpoints
A
- early pro B- DJ rearrangement on both chromosomes heavy chain
- late pro B- V-DJ on 1 chromosome of heavy- if constant region works with this variable region then stop, if not try on second, then apoptosis if neither work
- Pre-B- light chain- kappa 1 kappa 2, lambda 1, lambda 2 and can retry (V+J multiple times)-if none work- apoptosis
12
Q
Class switching from IgM to IgD
A
- RNA SPLICING!!!
- IgM and IgD constant regions are very close to each other on chromosome
- can do either or both in some ratio
- can make secreted or transmembrane if alternative splicing of end of RNA (2 extra exons for transmembrane)
13
Q
class switching
A
- constant regions are all on same gene
- DNA splicing moves variable region (VDJ) to new constant region
- can’t get old constant region back
- not by RAG
14
Q
mutations also take place
A
- somatic hypermutation
- takes place in whole V domain
- single base changes that are random
- does not take place in the constant region
- yields aa that improve binding to antigen they are selected for
- limited to variable region of Ig
- enzyme is AID-activated induced cytidine deaminase
- targets rearranged gene segments encoding variable region
- when B cells are most stimulated by T cells–class switch
15
Q
T Cells
A
NO SOMATIC HYPERMUTATION
everything else pretty much the same
-a/b (CD4/CD8) or d/g (innate)
-lower affinity to antigen
