Epitopy

Epitopy is a term used in immunology to refer to the functional surface on an antigen that is recognized by antibodies. Unlike a single epitope, which is the specific locality recognized by one antibody, an epitopy describes the clustered pattern of residues, shape, and electrostatics that constitutes the recognition interface for a group of related antibodies or for a class of antigenic variants. Epitopy emphasizes the topography of the antigen's surface rather than a single linear sequence.

Epitopes can be linear or conformational; epitopy often concerns conformational or composite surfaces formed by residues that may be distant in primary sequence but come together in three dimensions. In practice, epitopy is used in mapping studies to describe shared surface patterns across related antigens that explain cross-reactivity or broad neutralization.

Studying epitopy involves structural and mutational approaches. Structural methods such as X-ray crystallography or cryo-electron microscopy of antigen–antibody complexes reveal the contact surface. Mutational scanning, alanine substitutions, and peptide or phage display identify residues contributing to recognition. Computational analyses of surface properties also help define epitopes and epitopes across a family of antigens.

In research and vaccine design, epitopy concepts aid in identifying conserved surface patterns that can be targeted by broadly neutralizing antibodies. While the term is used variably and less standardized than epitope, it provides a useful framework for discussing how antibodies recognize related antigens across structural families.