Lecture 5 Flashcards
What encodes variable region of heavy chain?
V, D, & J genes
What encodes light chain?
V & J
How does VDJ gene varry in each cell?
- The organization of theses segments of the genes is the same in EVERY cell in the body EXCEPT the B/T cells in which they are rearranged allowing transcription
What happens in B cell development?
- During B cell development DNA rearrangement must occur in which 1 V segment is placed next to one J segment
- Everything between the two that are combined is deleted from that B cells genome
- RNA will then be made, spliced, translated to get us to antibody
Where does VDJ rearrangement occur?
Bone marrow
Precursor to B cells?
HSC
How many VDJ sements are there?
There are ~ 50 - 100 V gene segments
There are ~ 20 - 30 D gene segments
There are ~ 5 - 6 J gene segments
What is purpose of VDJ rearrangement?
The creation of a highly specific antibody
What is the order of the rearrangement?
- D if first moved by J then rearranged by V
All intervening material is deleted
The rearranged gene will end up close to the constant region
Which antigens drive the rearrangement?
This is not antigen driven
What is done in bone marrow transplant?
- Wipe out bone marrow and reconstitute it with HSCs
- CD34 + - the specific HSC that is used in bone marrow transplant
Significance of CD34+
HSC used in bone marrow transplant
What is the pro B cell?
- First stage in HSC development: HSC becomes pro B cell
- VDJ heavy chain rearrangement occurs here
- Once one allele rearranges, it wants to go to surface of cell so both heavy chains will be same
When does VDJ rearrangement occur?
Pro B cell stage
What is the Surrogate light chain?
- Binds to rearranged heavy chain and take it to surface of cell
What happens when heavy chain makes it to surface?
Signal sent to cell to stop rearranging so both heavy chains will be the same
What is the the pre B cell?
- What pro B cell becomes
- Turned off enzyme so heavy change no longer rearranged
- Enzyme will turn on again to rearrange light chain
What characterizes immature B cell?
IgM on surface
What do mature B cells do?
Immature B cells leave bone marrow to look for antigens to activate them
What is on surface of mature B cells?
IgM & IgD
What is true of IgM & IgD on matuer B cell?
- Variable region has same specificity
- Differnet antibodies however as constant region is not the same
What is allelic exclusion?
- Rearrangement is only occuring on one allele and the other is turning off
- Prevents one cell from making more than one antibody
What does allelic exclusion prevent?
B cell from having more than one antibody
What is RSS?
- “Recombination signal sequence”
- Conserved sequence found upstream of V and downstream of J
What is RAG?
- Recognizes RSS by V & J and cleave sequences between allowing V & J to come together to be ligated
- The two RSS’s are coming together to ligate to each other
What is BREC?
- “B cell recombination excision circle”
- Portion of gene between RRS segments that is cut out
How do you tell if bone marrow transplant is taking?
- BRECs will be seen
- Signals that new B cells are being made
What is difference between secreted and membrane IgMs?
- The difference is in the C terminal end that will or won’t sit in membrane
- There will be a secreted or membrane portion on 3’ end of conserved area
What determines if Ig is secreted or membrane?
Splicing
What does IgD do?
- Noone really knows what IgD does, just know it is on surface of mature B cell
What is the order of the rearrangement?
- D if first moved by J then rearranged by V
- All intervening material is deleted
- The rearranged gene will end up close to the constant region
What does IgD do?
- Noone really knows what IgD does, just know it is on surface of mature B cell
What is the light chain coded for?
Variable region - encoded for by V & J
Constant regoin - C exon
How is heavy chain coded for?
Variable region - VDJ
Constant region - multiple C exons
Where is c regoin found?
3’ end of v genes
First step in antibody creation?
Gene rearrangement
What happens after V moved next to DJ?
All D segments 5’ of rearrangment are deleted
Which cells does VDJ rearrangement occur in?
Only those commited to becoming B lymphocytes
What is predominant serum Ig?
IgG
What is predominant secretory Ig?
IgA
Most B lymphocutes have membrane Ig of what class?
IgD
IgM
How much more IgM is there in serum than IgE?
1000x
Antibody fragment with single comining site is designated?
Fab
Ig classes can be distinguised base on?
Their heavy chains
First step in rearrangement of heavy chain?
D brought next to J and stuff in between has been deleted
What is Fab?
Variable region
