A cell surface (membrane bound) antigen receptor (TCR) formed by 2 polypeptides – α chain and β chain
Unconventional T cells have antigen receptors formed by gamma and delta chains.
Each T cell has receptor of unique specificity
Does TCR bind to the antigen directly?
No, it will only bind to fragments of antigens (peptides) that are bound to major histocompatibility complex (MHC) proteins on the surface of the target cell
What are the 2 types of MHC?
Class I and Class II
MHC class I: overall structure similar but α polypeptide is larger and forms complete peptide binding domain β2microglobulin
-(β2m) is not transmembrane domain
What is the structure of MHC II:
What does it look like when a T helper cell binds via TCR to an MHC II complex with a peptide?
-Alpha helices (shown in red) along with the peptide are recognised by the TCR
- So its not just the peptide or just the MHC that it recognises, they are recognised by TCR when together.
What is CD3?
Complex of 6 transmembrane proteins
Forms part of TCR complex and transmits activation signal
Do CTLs express CD4?
No, but they express CD8 in association with the T cell receptor
What is CD8?
A dimer & type of protein on the plasma membrane of T-cells
TCR of CTL is associated with CD8 which binds to MHC I
What are the differences between MHC class I & II proteins?