Last updated: July 30, 2018

What Does Hapten Mean?

A hapten is a small molecule that does not trigger the production of antibodies but can react with an antibody.

Antibodies react with antigens by forming chemical bonds at specific sites called epitopes on the antigen molecule. Usually very small molecules, a hapten is capable of binding to the antibody but alone does not trigger the body's immune system. It is sometimes described as an incomplete antigen or an antigen that is not immunogenic.

However, haptens can stimulate an immune response thus triggering the production of antibodies if they are attached to a carrier protein. The combination of the hapten and larger carrier protein molecule renders the completed antigen recognizable by the body's immune system.


WorkplaceTesting Explains Hapten

Many antibiotics, such as penicillin, are haptens. These drugs work by attaching to proteins in the body. Once bound to these protein molecules, the newly formed antigen can then bind to antibodies and prompt the body's immune system into action.

In some instances, haptens may act as imposters and inhibit the immune system. This happens when antibodies attach to the hapten rather than the larger antigens that triggered the initial immune reaction.

Many drugs of abuse are haptens and thus can attach to specific antibodies. This characteristic can be used to test for the presence of drugs of abuse in a specimen of bodily fluid. An immunoassay test employs specific antibodies and a multi-step process to determine the presence a targeted drug (the hapten) in a specimen.


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