Immunology Lecture 5. Flashcards
What is included in the light chain locus? Heavy chain locus?
Light chain: V, J, (kappa or gamma) Heavy chain: V, D, J
How are V, D, & J brought together?
unique enzymes induced by recombinase genes: RAG1 and RAG2 - pull ends of DNA together, while another enzyme ligates, followed by TdT addition of n-nucleotides
What is formed by the RAG complex?
A DNA hairpin and then opens hairpin to generate palindromic P-nuclotides
How are the V, D, and J joined after ligation by RAG?
TdT - an enzyme that adds random nucleotides with no template until there is overlap and then an edit-repair enzyme comes and fixes it up - an exonuclease removes unpaired nucleotides
Where are N-regions (N-nucleotides) found?
only heavy chains - NOT light chains
What is the importance of N and P nucleotides?
add a bit of randomness to the splice site -> junctional diversity
When is H-chain gene rearrangement checked?
after V-DJ rearrangement (no checking after D-J rearrangement) 2 chances
When is L-chain gene rearrangement checked?
after H-chain works - start with K twice and then try L twice
How does switching from IgM to IgD happen?
selective splicing of PRIMARY RNA TRANSCRIPT - no class switching involving gene rearrangements
How does switching between transmembrane and secreted immunoglobulin happen?
selective splicing of primary RNA transcript
How does class switching occur?
a variable region is joined to a new constant region except to IgD
What is the function of AID? (activation induced deaminase)
class switching (by splicing) and somatic hypermutation (which ends up improving binding to antigen) - single base changes in hypervariable region (CDRs)
When does AID function?
during immune response with T cell help
What is the one mechanism that works for generating B-cell diversity but not T-cell diversity?
somatic hypermutation
Can the IgM to IgG class switching be reversed?
NO - those genes are spliced out
