What are haptens known for?

Haptens are small molecules that, on their own, cannot elicit an immune response because they are too small and lack the necessary complexity to be recognized by the immune system as a threat. However, when they bind to larger carrier proteins (which serve as immunogens), they can alter the structure of these proteins in a way that makes them recognizable to the immune system. This binding leads to the formation of a complex that can then trigger an immune response. Thus, the defining characteristic of haptens is their ability to bind to larger molecules, which allows them to be recognized by immune cells, thereby activating an immune response in conjunction with those larger molecules.

This interaction highlights why haptens are not classified as large immune molecules themselves, cannot elicit an immune response alone, and do not serve as a common type of antigen on their own. Their unique function in the immune response is centered around their role as small entities that must associate with larger immunogenic components to be immunologically relevant.