gusah193

Hello, so what i've learnt so far is that engulfed antigen's peptide will be presented on the surface of antigen presenting cell with MHC class II, and CD4 T cell will see it and trigger humoral immune response. And for the MHC class I, the virally infected/intracellular peptide will be cut up by proteosome and sent to the surface for CD8 T cell to recognize. My lecturer said that if the peptide of the antigen is first-seen in this case, the CD8 T cell will not activate immediately, but it will signal the infected cell to go to lymph node where they can be cross presented. My question here is, will this happen to every first-seen peptide of an antigen? and even if it is not first-seen, and T cells have memory of it, wouldn't it take a while for T cells to be educated in thymus and be sent out to lymph nodes? that means no CD8 T cell will immediately activate and kill. yeah? And what if the first seen peptide is extracellular and it's been engulfed by phagocytes like the first scenario, will MHC class II and CD4 T cell be able to detect the new foreign peptide? Thanks so much guys I apologize if my grammar is bad and you have trouble understanding it