2. T Cells Flashcards
T cell function
- To provide help to B-cells and secrete cytokines
- To kill virally infected cells
CD8+ T-cells
recognise MHC 1 molecules
cytotoxic
CD4+ T-cells
recognise MHC2 molecules
helpers
further subdivided into TH1 and TH2
T-cell selection in the thymus
T-cell precursors enter the thymus
TCR gene rearrangement is initiated
T-cell receptor (TCR) that binds weakly to self MHC are positively selected and survive
Those that do not die by default
T-cells that bind too strongly to self are induced to die
Where does T cell Selection take place
thymic medulla
What % of thymocytes survive selection
5%
TCR vs Antibody
TCR = 2 polypep. chains
Ig = 4 polypep. chains
Both have constant and variable regions
Gene rearrangement occurs in development of both
no somatic hypermutation of the TCR
TCR and CD3
TCR associates with the CD3 complex
CD3 complex transduces signal received by the TCR
CD4+ T-cell signaling after APC engagement
Binding of ligand to the receptor
phosphorylation of the ITAMs by Lck
ZAP-70 binds to the phosphorylated ITAMs and is activated
Mutation in ZAP-70
leads to SCID
Caused by defective CD4+ T-cell function
T-cell signaling =
T-cell proliferation
IL-2 binds to receptors on the surface of both CD4+ and CD8+ T-cells
T-cell proliferates
forms an “army” of identical T-cells
T-cell-B-cell interactions
B cell is triggered when it encounters its matching antigen
B cell engulfs the antigen and digests it
Antigen fragments displayed on MHC
Antigen-MHC complex attracts help of mature, matching T cell
Cytokines secreted by the T cell help B cell to multiply + mature
plasma cells release antibodies in to blood
TH1
associated with cell mediated immunity
TH2
associated with antibody mediated immunity
TH1 TH2 regulation
Activated TH2 cells secrete TGF-β and IL-10
IL-10 and TGF-β inhibit growth of TH1 cells
Activated TH1 cells secrete IFN-γ
IFN-γ inhibits proliferation of TH2 cells
