just a question regarding antigen first observed in adaptive immunity

[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

Edited March 30, 2015 by gusah193

[Xalatan]

You may be confusing the function of APC vs. that of CD8+ Tc cells.

 

If a CD8+ lymphocytes binds to and is activated by the MHCI molecule on a virally infected cell, it receives a second signal via T Helper cells, eg. IL-2. Co-stimluation by MHC-1 and Th will activate the cytotoxic T cells on site, to release perforin, granzyme, and CD95L to apoptose the virally infected cell in situ. This is why Tc cells are called cytotoxic.

 

APCs in the skin will process external antigens, present them on MHC II, and travel to the regional lymph nodes for paracortical activation.

 

If the antigen happens to be in the blood, then it will be circulated to the spleen instead of lymph nodes for white pulp activation. So the site of antigen presentation isn't always in Lymph nodes, it depends on whether the antigen has access to haematogenous or lymphatic circulation - much like different routes of cancer spread coincidentally.

Edited December 27, 2015 by Xalatan