Epitopes

From Proteopedia

An epitope is the portion of the surface of an antigen that binds to an antibody, or the peptide fragment of a protein antigen that binds to the T lymphocyte antigen receptor when presented by the cognate major histocompatibility protein. The best way to identify an antibody epitope is from a crystal structure of the antibody:antigen complex, where the contacts are evident. There are several servers that attempt to predict epitopes.

Terminology

Antibody epitopes may also be called determinants, which is a historically earlier but equally good term. The term epitope implies that the determinant is on the surface of the antigen ("epi"). It is unfortunate that epitope has caught on as the term to describe the peptide fragments that T cells recognize, since these are not on the surfaces of protein antigens, but fragments which may have been buried in the folded protein.