What is the term for an area on an antigen that is recognized by the immune system as nonself?

• A. Hybridoma
• B. Antidote
• C. Epitope
• D. Clone

Answer: (C)

The area on an antigen that the immune system recognizes as nonself is called an epitope. An epitope is the specific surface feature—the binding site—that antibodies or T cell receptors interact with. It can be a short linear sequence of amino acids or a three-dimensional shape formed by the folded protein. A single antigen may have multiple epitopes, each capable of triggering an immune response. The other terms don’t describe this recognition site: a hybridoma is a lab-created cell line that produces monoclonal antibodies; an antidote is a remedy for poisoning; a clone refers to a genetically identical group of cells. Epitope is the pinpoint that the immune system targets.