Flashcards in Chapter 4 Deck (117)
What is the fundamental difference between TCR and BCRs?
BCRs can recognise free antigen whereas TCRs can only respond to peptide presented by MHC
What is the benefit of TCR vs BCR receptors?
TCRs can respond to antigens confined within cells
What is the major difference between MHC classes I and II?
MHC class I present peptides from intracellular sources whereas MHC class II- extracellular
What is the structure of a TCR?
transmembrane molecule composed of 2 disulfide-linked chains a and b
How are the alpha and beta chains of the TCR organised?
folded into 2 domains- one with invarian structure and one with high dgree of variability- like Fab fragment
How many hypervariable regions does each variable region of the TCR have?
What is the name of the hypervariable regions found on TCRs?
CDR- complementarity determining regions
What is the function of the CDRs?
contain the amino acids which make contact with the pMHC
What is found on the cytoplasmic tail of CD4 and CD8?
bound to tyrosine kinase Lck
What is the function of Lck?
initiates signal transduction cascase following encounter of T cell with antigen
What is the structure of CD4?
single-chain polypeptide containing 4 Ig-like domains which form an extended rod
What is the structure of CD8?
disulfide-liinked heterodimer of a and b chains which each have a single Ig-like domain contnected to a glyosylated polypeptide
What is the ab TCR known as?
Where are yd TCRs mainly found?
What is the difference between T-cells expressing ab TCRs and yd TCRs?
yd do not require MHC for antigen detection and often do not express MHC co-receptors (CD4 and CD8)
What is the function of CD4 and CD8?
act as coreceptors for TCRs
Why may yd T-cells be involved in regulation of the immune system?
recognise molecules that appear on activated T cells
What complex is associated with the TCR?
What is the function of CD3?
relays signal to the interior of the T-cell to act on ligation of antigen
What is the structure of the CD3 molecule?
a ye dimer; a x-x dimer and de dimer
what is the function of the fourth hypervariable region of beta chain of a TCR?
binding site for superantigens (not pMHC)
What is found in the cytoplasmic domains of CD3 peptide chains?
immunoreceptor tyrosine-based activation motifs
What are ITAMs linked to?
src protein tyrosine kinases
What happens to the ITAMs on the CD3 compex when TCR meets p-MHC?
phosphorylated by the Lck tyrosine kinase on CD4/CD8-- recruitment of proteins---etc
Why would a cell express non-classical MHC class I molecules?
cell stress of DNA damage
What type of PRR are particularly suited to inducing the expression of type I interferons?
ones situated within the intracellular compartments- TLR3, TLR7-9, RIG-like helicases
What is one of the downstream consequences of interferon secretion?
cessation of protein synthesis and therefore downregulation of MHC molecules
what do inhibitory receptors on NK cells have on their cytoplasmic tail?
ITIMs- immunoreceptor tyrosin-kinase inhibitory motifs
What is the function of ITIMs?
recruit phosphatases eg SHP-1 which antagonise signal transudction