épitope

An epitope, or antigenic determinant, is the specific part of an antigen that is recognized by an immune receptor. For B cells, epitopes are the surfaces of proteins or other macromolecules that antibodies bind directly. For T cells, epitopes are short peptide fragments presented by major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells. The recognition of epitopes drives adaptive immune responses and influences vaccine design and diagnostics.

Epitopes can be linear (continuous) sequences of amino acids, or conformational (discontinuous) formed by amino acids that are brought into proximity in the folded protein. Most B-cell epitopes are conformational, whereas T-cell epitopes tend to align with specific lengths compatible with MHC binding. Epitopes can also be carbohydrate or lipid moieties (glycoepitopes or lipopeptidopes).

Mapping and prediction of epitopes involve both experimental and computational approaches. Experimental methods include overlapping peptide libraries, phage display, and structural analysis to identify regions recognized by antibodies or T cell receptors. Computational tools predict B- and T-cell epitopes based on sequence, structure, and MHC-binding motifs, aiding the design of vaccines and diagnostic reagents.

Clinical relevance of epitopes includes vaccine design, where multi-epitope constructs aim to broaden protection; antibody therapeutics that target specific epitopes; and the study of allergen and autoantigen epitopes. Concepts such as immunodominance and cross-reactivity influence the magnitude and scope of immune responses to different antigens.