Glossary · concept
Epitope
The specific small piece of a molecule that an immune receptor actually binds — the precise “handle” the immune system grabs.
An antigen is any molecule the immune system can react to; an epitope is the exact sub-region that a T-cell receptor or antibody physically binds. For T-cell responses the relevant epitopes are short peptides — typically 8–11 amino acids — displayed on the cell surface.
A neoantigen is useful only if its mutated region forms an epitope that is both presented on HLA and recognized by a T cell. “Epitope prediction” — guessing which peptides will become functional epitopes — is one of the core machine-learning tasks in the field.