Lecture 6 Flashcards
What is major rule of antibody synthesis?
- Single B cell only makes one type of antibody
- Occurs by allelic exclusion
- Same is true for plasma cell
- Only one type of H chain and one type of L chain
What has occured in ProB cell?
- Heavy DJ rearrangement
- No light chain rearrangement
When does DJ rearrangement occur?
ProB stage
What do mature B cells have on surface
IgM & IgD with same variable region
What mediates VDJ rearrangement?
RSS
What do RAG1/2 do?
Enzymes that recognize and align RSS and cleave sequence between
Are all RAG rearrangements functional?
No
How do IgM and IgD end up on same cell?
Alternative splicing of nuclear RNA
What is junctional diversity?
- N region addition
- Nucleotides (B sequences) not present in germ line that are added to junctions of rearranged VDJ during rearrangement
- Adds to diverstiy
What facilitates junctional diversity?
TdT
3 contributions to Ig Diversity?
- VDJ rearrangement
- Junctional diversity
- Combination of H & L chain
What happens to non functional VDJ rearrangements?
They are deleted
What happens to self reactive B cells?
- Become anergic
- Deletion
- Rescued by receptor editing
What happens to self reactive B cells?
- Become anergic
- Deletion
- Rescued by receptor editing
Where does isotype switching occur?
In periphery, not in marrow
What causes isotype switching?
B cell interaction with antigen
What can isotype switch result in?
IgG
IgE
IgA
What is necessary for isotype switch?
- AID - Enzyme that will cleave loop
- Cleaved region is ligated associating VDJ region with new gene
- Cleaved region is deleted from genome
Can B cell undergo multiple isotype switches?
Yes
Where does generation of antibody diversity occur?
Generation of antibody diversity occurs in bone marrow in antigen independent manner
What is hypermutation?
- Variable regions of Ig genes undergo BP mutation of 1/1000 when leave marrow
- Known as hypermutation as rates exponentially greater than what’s seen in normal cells
- Results in AA change in binding site changing its specificity
- This does not occur in the bone marrow and this IS in response to antigen
Is hyermutation in response to antigen?
Yes
What is an anegic cell?
- Non responsive, will not be activated when react with self
- This can happen to self reactive cells
What is danger of anergic cells?
- Dangerous if become mutated and become activated
- Cause autoimmune disorders
What is receptor editing?
- Rescues self reactive B cells by changing receptor
- Instead of getting signal to die, RAG is upregulated allowing for another VJ rearrangement resulting in new B cell that is hopefully not self reactive
What is receptor editing?
- Rescues self reactive B cells by changing receptor
- Instead of getting signal to die, RAG is upregulated allowing for another VJ rearrangement resulting in new B cell that is hopefully not self reactive
- Only happen on light chain
Can receptor editing happen on heavy chain?
- Cannot happen on heavy chain as all the “D’s” were deleted in initial rearrangement
- However, simply changing light chain changes specificity of receptor
Which chain rearranged first?
Heavy
Which chain rearranged first?
Heavy
How many epitopes does T cell recognize?
Only one
How many epitopes does T cell recognize?
Only one
Chains on T cell?
- Alpha and Beta
- Each chain has variable and constant region
- Their variable regions come together to make binding site
Is T & B cell concurrent in bone marrow?
No, T cells made in thymus
T and B cell on same chromosomes?
Yes
What are alpha and beta chains product of?
Alpha chain - product of V J rearrangement
Beta chain - product of VDJ rearrangement
Do T cells demonstrate allelic exclusion?
Yes
What mediates Rearragement in t cell?
Rag
What ar TRECs?
- T cell rearrangement excision circles
- Intervening DNA that is removed and deleted in rearrangement
How do you tell if patient is making Trecs?
See if they have TRECs
Different in T & B cell formation?
- T cells do not display somatic hypermutation
- T cells do not display isotype switch
- T cells do not display differential splicing to get membrane & secreted form
T/F: IG are encoded by gene segements on same chromosome?
False - Each family is on different chromosome
T/F: one Ig can have two types of light chain
False
T/F: myeloma proteins are result of polyclonal B cell activation
False
T/F: In pre B cells both heavy and light chain genes are rearranged?
False
When is hypermutation highly active?
Generation of memory B cells
What has rearranged in Plasma Cell?
VDJ on one allele
VJ on other allele
What has rearranged in Pre B lymphcyte?
No VJ
DJ on one allele
VDJ on other allele
Main anitbody of primary response?
IGM
Main antibody in secondary response?
- IGG
- IGG levels stay high longer here than IGM does in primary
Explain secondary reagent?
- Inject Human IGG in animal and they make antibody it
- Take human blood and mix with tetanus or something you were vaccinated for hoping that it will bind the antigen in tray
- Take the animal generated antibodies to IGG and add them to tray and they should bind the human IGG
- You label animal antibody with something you can detect
- Secondary antibodies are directed against FC region of antibody
