Antibodyantigen

An antibody-antigen interaction refers to the specific binding between an antibody, produced by B cells, and an antigen, a molecule or part of a molecule capable of eliciting an immune response or being recognized by the immune system. Antigens are typically proteins or polysaccharides, though lipids and nucleic acids can be antigenic. The specific portions recognized by antibodies are epitopes.

Antibodies (immunoglobulins) have variable regions that form the antigen-binding site. Binding is highly specific and depends on shape, charge, and hydrophobic interactions. Affinity describes the strength of a single binding site; avidity describes the overall strength when multiple sites participate. Interactions are non-covalent, allowing reversible binding.

Outcomes of antibody-antigen binding include neutralization of pathogens, blockade of functional sites, opsonization to promote phagocytosis, activation of the complement system, and agglutination of particles. In B cells, antigen binding followed by T cell help drives antibody production and class switching, increasing duration and scope of protection.

Antibody-antigen complexes can be detected in serological assays, and lie at the core of diagnostics, vaccines, and biologic therapies. Monoclonal antibodies are engineered antibodies that target specific antigens for therapeutic or diagnostic use. Epitope mapping, cross-reactivity, and affinity maturation influence the effectiveness of antibody-antigen interactions.