This might sound very basic question, but please share with me an explanation of how the T cell is activated when the antigen is not a peptide? What happens? And what are the molecules involved in terms of cytokines and receptors?
Peptide antigens are recognized by T cells via the T-cell receptor (TCR). These antigens are recognized in the context of class I and class II MHC molecules.
T cells also have PRRs, such as the Toll-like receptors and the C-type lectin receptors. These are separate molecules on the surface of the T cells that bind their target antigens - many of which are polysaccharide compounds - independent of the TCR complex.
You need to be more specific in your question, this is a very large topic that have several answers.
In general, alphabeta T cells require CD3 activation for activation (and recognize peptides), and a slew of co-stimulatory molecules. And while PRRs (like TLRs) can serve as co-stimulation and/or push and pull T cell activation towards a certain pathway, they usually cannot activate T cells by themselves.
Now...there are T cells with TCRs that do not recognize peptides, non-peptide moieties… These are classified as unconventional T cells as a whole and includes CD1 restricted T cells, gammadelta T cells, and innate T cells (which includes MAITs...).
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