MHC-II proteins are presenting antigens on the surface of cells with lysosomal activities where they eventually might get transported off by some T-cell receptor-anti-gens, as far as I understand (pls apologise and correct me if I am wrong). I would be interested in two questions regarding this specific immuno-cascade reaction.
It appears that in cases self-pepties are bound to the MHC-II proteins (say HLA-DP2) when they are at the surface already. Where do such self-peptides come from? Do they come from inside the endosomal active cell or could they also come from "outside" from where the T-cell comes?
What would happen if (for some reason) a) the self-peptide binds "irreversibly" to the MHC-II? b) the self peptide binds irreversibly to the MHC-II and at the same time is structurally significantly distorted (e.g. if there is something, like a heavy metal bound in-between the MHC-II and the self-peptide)?
(I apologise for the case I got some terminology wrong or some basic concepts, I am no specialist in bio-chemistry.)