Lecture 31 Flashcards
TCR structure
Composed of an alpha and beta chain
Each has a variable and constant region
Contents of alpha chain of TCR
Multiple V and J segments
Contents of beta chain of TCR
Multiple V, D, and J segments (like heavy chain in BCR)
Where does TCR somatic recombination take place
Thymus, irreversible
Combinatorial diversity of TCR in alpha and beta chain
Alpha chain–> VJ
Beta chain–> VDJ
Combination of alpha and beta chain
Similarities in mechanisms of TCR and BCR recombination
1) V, D, and J segments are flanked by RSS recognized by RAG 1 and 2
2) Artemis cuts DNA hairpins
3) TdT adds non-coded nucleotides in the joining regions
Differences in BCR and TCR recombination
BCR
Ig Heavy chain–> D segment is surrounded by 2 RSS BOTH with 12-bp spacing
TCR
Beta chain–> D segment has a 5’ 12bp RSS and a 3’ 23bp RSS
How many CDRs does TCR have per chain
3 CDRs per chain
Which CDR in TCR is the most important for diversity
CDR3
Where are CDR1 and 2 encoded in TCR
Within V segments of alpha and beta chains
Where is CDR3 encoded in TCR
In the D and J segments
What does Allelic exclusion ensure
That each B cell synthesizes only 1 allele for a heavy chain and 1 allele for a light chain
(through genomic silencing of other chromosomes (methylation))
Consequence of Alternative RNA splicing
1) Expression of IgM vs IgD
2) If immunoglobulin is secreted vs transmembrane
5 Isotypes of Heavy chains BCR
1) M (mu)
2) D (delta)
3) G (gamma)
4) A (alpha)
5) E (epsilon)
Which immunoglobulin classes have variants
IgG and IgA
