What is a hapten?

A hapten is best defined as a very small molecule that can bind to a larger carrier molecule. Haptens themselves are not immunogenic, meaning they cannot stimulate an immune response on their own due to their small size. However, when they bind to larger protein molecules (the carrier), they can form a complex that can elicit an immune response. This is significant in immunology because it illustrates how certain small molecules, when associated with larger proteins, can be recognized by the immune system as foreign and potentially provoke an immune reaction.

In contrast, large antigenic molecules refer to full antigens that can independently stimulate an immune response, differentiating them from haptens. Antibodies, which are a type of protein produced by the immune system, specifically bind to antigens, but they are not haptens themselves. Cytokines play a role in cell signaling and modulating immune responses but do not fit the definition of a hapten either. Understanding these distinctions is crucial in the study of immunology and the interactions between haptens, carriers, and immune responses.