haptènes

Haptens are small molecules that are too small on their own to elicit an immune response but can become immunogenic when attached to a larger carrier molecule, typically a protein. This complex of hapten and carrier is then recognized by the immune system. The term "hapten" comes from the Greek word "haptein," meaning "to fasten."

The hapten itself binds to specific sites on antibodies. These sites are part of the antibody's antigen-binding fragment (Fab). When a hapten is conjugated to a carrier protein, it creates a new antigen. The immune system can then mount a response against this complex. Antibodies are produced that recognize the hapten, and sometimes also the carrier, or a combination of both.

Haptens are important in understanding immune responses and have practical applications in diagnostics and immunology research. For example, in drug allergy testing, drugs can act as haptens. If a drug binds to a body protein, it can form a hapten-carrier complex, triggering an allergic reaction in susceptible individuals. The ability of a hapten to bind to an antibody is determined by its chemical structure and its complementarity to the antibody's binding site. The binding is typically reversible. Understanding hapten-carrier interactions is crucial for developing vaccines and diagnosing certain allergic conditions.