Antihapten

An antihapten is an antibody that binds a hapten, a small molecule that is not immunogenic on its own but can elicit an immune response when covalently linked to a larger carrier protein. Haptens are typically recognized by B cells only in the context of a hapten-carrier conjugate, because T helper cells respond to epitopes on the carrier and provide the signals needed for B cell activation. Consequently, the antibody response to the hapten is usually dependent on the carrier protein used in immunization.

Antihapten antibodies are generated by immunizing with hapten-carrier conjugates and then isolating serum or creating monoclonal antibodies. They are highly specific for the hapten moiety, though cross-reactivity can occur with structurally related molecules. Some antihapten antibodies can bind free hapten in solution if the affinity is sufficient.

Applications of antihapten antibodies include diagnostics and research. In competitive immunoassays, they detect or quantify small-molecule analytes such as drugs, hormones, or environmental chemicals. Dinitrophenyl (DNP) is a classic hapten used in studies of antihapten responses. Other common haptens, such as digoxigenin or fluorescein, are used in immunoassay systems as model haptens. Anti-hapten antibodies thus enable detection of hapten-labeled substances and facilitate assays for small molecules that would not be detectable by antibodies against larger macromolecules.