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Subject - Immunology

The epitope, also called the antigenic determinant, is the specific region of an antigen that interacts with the antigen-forming part of an antibody, also known as the paratope. It may also bind to a T cell receptor.

An epitope can theoretically be constructed in two ways: as a continuous epitope made of a single, unbroken sequence of amino acids, or as a discontinuous epitope made of amino acids that are not sequential in the primary structure, but are brought into close contact upon folding of the protein.

Depending on its size and structure, an antigen may contain many different epitopes. Monoclonal antibodies are directed exclusively against a specific epitope of an antigen, whereas the various antibodies of a polyclonal serum recognize several epitopes of a single antigen.

A special case is presented by the haptenes. These are generally small molecules that display an epitope and can bind specifically to a corresponding antibody; however they are not able to initiate an immune response if they are not bound to a carrier protein.

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