Adaptive immunity 2 Flashcards
ITAM
Immunoreceptor tyrosine based activation motif
B cell receptor
2 heavy chains
2 light chains
T cell receptor
1 alpha chain
1 beta chain
Resting B cell
Has membrane bound immunoglobulin
- IgM
- IgD
Resting B cell encounters antigen
Stimulates proliferation signal
Leads to generation of memory B cell and plasma cells
Plasma cells secrete immunoglobulin
Irreversible changes in immunoglobulin
Requires changes in base combination in DNA of loci
Reversible changes in immunoglobulin
Require changes in splicing
Light chain rearrangement
Single step VJ recombination
Heavy chain rearrangement
Involves a DJ recombination event followed by a VDJ rearrangement
B cell
44 variable regions
27 diversity regions
6 joining regions
3x10^11 possible combinations
Leads to genetic diversity
How does rearrangement occur?
Between specific sites on the DNA called recombination signal sequences (RSSs)
Rearrangement is catalysed by two recombination activating genes: RAG-1 and RAG-2
RAG-1 and RAG-2
Bind to an RSS sequence
- at the end of every V, D and J segment
Loop of DNA made by binding is spliced out
Catalysed by a group of enzymes
End up with a circularised bit of DNA
Two ends of DNA left floating are rejoined with DNA ligase and terminal deoxytransferase
Somatic hypermutation targets
The rearranged gene segments encoding the variable region
Class switch recombination
Same receptor, different constant region allowing the cell to perform a range of effector functions
Constant regions are spliced out using switch regions located upstream of each constant region
First cut is always just before the Cu region
The second cut is determined by the cytokines secreted by follicular T helper cells
First target switch region
Always the Su switch region
