Lecture 6 Flashcards
What are the 4 mechanisms that generate antibody diversity?
- Somatic recombination
- Imprecise recombination junctions
- Combinational pairing
- Somatic hypermutation
Which antibody diversity mechanisms occur BEFORE antigen stimulation?
-Somatic recombination
-Imprecise junctions
-Combinatorial pairing
Which antibody diversity mechanisms occur AFTER antigen stimulation?
Somatic hypermutation
True or false: the 4 mechanisms of antibody diversity occurs in both the variable and constant regions
False
-happens in VARIABLE regions of light and heavy chains
What happens in somatic recombination?
Alternative versions of the variable region (variable, joining, and diversity) are brought together by DNA rearrangement
How many segments are encoded by the variable light chain?
2
-Variable
-Joining
How many segments are encoded by the heavy chain?
3
-Variable
-Joining
-Diversity
True or false: The variable light chain has a diversity segment
False
-Only variable and joining segment
Where does rearrangements of the V and J occur?
Germline
-At DNA level
How does somatic recombination lead to B cell diversity?
By randomly picking pieces there are many different versions of B cell for variable region sin the light and heavy chains that will make different specificity
True or false: Only developing B cells rearrange their Ig loci
True
How does gene recombination work?
RAG proteins bind to RSS (signal sequence) flanks segments that need to be recombined and breaks DNA at the joint
How is a coding joint formed?
RAG gets rid of a portion of immunoglobulin loci which brings V and J making a coding joint
How does imprecise recombination further increase diversity?
Uses TDT enzyme that adds nucleotides to junctions after RAG cleaves
-Adds/subtracts nucleotides RANDOMLY to each developing cell which makes diff junctions
Why does CDR3 have the highest variability?
Has 2 imprecise junctions
What is combinatorial pairing?
Pairs different combinations of heavy and light chains which adds diversity
What is somatic hypermutation?
Uses AID to introduce random mutations by using nontemplated nucleotides in variable region of light and heavy chain
-occurs after antigen stimulation
What is AID?
Used in somatic hypermutation
-introduces non-templated nucleotides that cause mutations to Variable region of light and heavy chain
Does AID affect the constant region?
No, only affects variable regions
Why can somatic hypermutation lead to antibodies withy higher, similar, or lower affinities?
Because it is a random process
Before antigen encounter, the only heavy chains expressed by mature B cells are?
u and delta
What does the Cu and Cdelta encode for?
IgM and IgD respectively
What regions determine isotype swtiching?
switch regions
Naive immature B cells express?
ONLY IgM
-only Cu region
Naive mature B cells express?
Can make both IgM and IgD
-make both Cu and Cdelta
-IgD CANNOT be secreted
What determines if Cu and/or Cdelta is made?
Alternative mRNA splicing
True or false: Alternative mRNA splicing is a type of isotype switching
False
It is not a type of isotype switching b/c does not use switch sites and isotype switching occurs AFTER antigen encounter
-Alternative mRNA splicing happens before antigen encounter
After antigen encounter occurs what is needed to do isotype switching?
T cell help (CD4 T cells)
Which isotypes occur before antigen encounter and isotype swtiching?
IgM and IgD
What happens when there is antigen stimulation accompanied by T cell help?
T cell help allows for isotype switching through induction of AID–>allows for switching
-Variable region does NOT change
Does variable region change during isotype switching?
No, it is the same from somatic recombination
- constant region changes
What happens when there is antigen stimulation without T cell help?
Only IgM is produced
-NO isotype switching
How do B cells secrete their receptor/antibody after activation?
Eliminate trans-membrane region via RNA processing
How does isotype switching work?
- BEFORE antigen encounter: Naive B cells only make Cu (immature) or Cu/Cdelta (mature)–>RNA splicing determines
- AFTER antigen encounter: isotype switching occurs via DNA recombination of switch sequences when AID is induced and T cell help
