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a factor that establishes the nature of an entity or event.
antigenic determinant a site on the surface of an antigen molecule to which a single antibody molecule binds; generally an antigen has several or many different antigenic determinants and reacts with many different antibodies. Called also epitope.
hidden determinant an antigenic determinant located in an unexposed region of a molecule so that it is prevented from interacting with receptors on lymphocytes, or with antibody molecules, and is unable to induce an immune response; it may appear following stereochemical alterations of molecular structure.
immunogenic determinant the part of an immunogenic molecule that interacts with a helper T cell in triggering antibody production as opposed to the antigenic determinant or hapten, which interacts with B cells.