Question

• Explain how T cells are primed and how they differ from the effector phase. Make certain to be able to talk specifically about the MHC/T cell receptor interaction and CD28/B7 activation signals as well as the PD-L1/PD-1 and CTLA4/B7 inhibitory signals

Answer 1

T cells are primed by Antigen presenting cells . These cells have MHC molecules on their surface to present the antigen .

MHC II having antigen presenting cells present to CD4 + T cell and activate them . MHC I having antigen presenting cells present to CD8+ T cells . This MHC - TCR interaction in signal 1 . But for them to become effector cells they need Signal 2 which is provided by B7 proteins , Like CD 80 and CD 86 present on APC's . This interacts with CD 28 on T cell . B7 proteins are expressed on APC after innate immunity is activated . However if the APC preset self antigen , instead of B7 proteins , inbhitory CTLA-4 and PD-1 are expressed and effector cells are not formed.