Adaptive Immune responses; T cells Flashcards
What are the molecules that all T cells have?
CD4 and CD8
When are CD4 and CD8 both expressed on T cells?
When they are immature.
What does maturation of T cells involve?
The suppression of either CD4 or cD8
Which T cells mainly have CD4?
T helper cells and T regulatory cells.
Which T cell mainly have CD8?
Cytotoxic T cells
How do T cells recognise antigen?
Via the TCR
What is the structure of the TCR?
It is a heterodimer with alpha and beta chains, however a subgroup of T cells have heterodimer of gamma and delta chains. The TCR is antigen specific with a variable (V) and contstant (C) regions. The TCR does not recognise whole antigens, instead it recognises epitopes.
Describe the structure of the TCR.
The variable region is most distal to the cell membrane and the constant region is most proximal. There is then a transmembrane sequence anchoring it to the plasma membrane with an intracellular carboxyl terminus.
What do CD4/8 recognise?
part of the MHC that is constant in every individual for tissue compatibility. MHC-1 recognises CD8 and MHC-II recognises CD4
What does the variable region of MHC do?
Holds the peptide antigen which is then presented to the TCR (MHC-II).
What are the difficulties underlying cell signalling in T cells?
The short carboxyl tail does not have enough amino acids fro recognition by kinases, so the TCR has ITAMs (Immunoreceptor tyrosine-based activation motif) which is recognised by tyrosine kinases which phosphorylates the tyrosines, activating and initiating signalling in the cell.
Name an example of a tyrosine kinase in T cells.
LCK (lymphocyte specific protein tyrosine kinase)
Name the two sets of CD3 co-receptor complexes
CD3 molecules (3 types delta, gamma and epsilon. And homodimer zeta chains
How are the variable regions of T cells created?
Through genetic recombination of TCR genes; randomly generated variability requires subsequent selection of T cells recognising the correct peptide-MHC combination i.e. the foreign peptide and self-MHC. Recognition of self-petides can occur.
Where does the selection of T cells occur?
In the thymus; positive selection of the ability to recognise self-MHC
Negative selection for the recognition of peptides of self antigens.
MHC-I in humans are which HLA?
A B and C
MHC-II in humans are which HLA?
DP, DQ, DR
What happens if when a T cell only recognises peptide-MHC?
It does not activate the T cell, it becomes functionally inactivated (anergy) and cannot elicit an immune response. Activation of T cells requires co-stimulation
What are the co-stimulatory molecules of APCs?
B7 and ICAM; become expressed at higher levels in response to infection. These co-stimulatory molecules bind to receptors on the T cell surface; B7 - CD28 and ICAM-1 - LFA-1. This occurs alongside MHC-II - TCR
How else can T cells become activated?
Through cytokines binding to cytokine receptors.
What does activation cause T cells to do?
Proliferate, mediate effector functions and form memory cells, however most become effector cells.
Mutual antagonism occurs between which T cells?
Th1 and Th2 to aid in differentiation of infections; bacterial or viral respectively.
What does Th1 express and do?
Produces: IFN-gamma, IL-2 and TNF beta
Function: Aids Tcyt cells, macrophages and some B cells. Inhibits Th2 cells
What does Th2 express and do?
Produces: IL-4/5/10/13
Function: aids B cell function and inhibits Th1
