I have seen the answer to this question which says that T cells do not express MHC II proteins which would make sense.
However, my textbook "The immune system" by Peter Parham disagrees. It says that T cells do gain MHC II receptors after activation.
*Activated T cells express MHC class II molecules, whereas resting T cells do not.
I cannot see why this is needed. MHC II molecules are for CD4 cells (helper T cells).
If the T cell presenting the antigen was a CD4 cell, then that seems useless, because this cell was already the one that could recognise this particular antigen - so why show it to others? The chance that another T cell that could recognise it too would be incredibly small no?
I guess I can see the merit of a CD8 T killer cell to show the antigen, as it could alert other CD4 T cells to come assist (although cytokines seem like a better method...)
So what is the purpose of T cells, in particular CD4, of showing MHC II proteins?