Michael Sela, Department of Chemical Immunology, The Weizmann Institute of Science, Rehovot, Israel

Immunogen is a substance (molecule) capable of provoking an immune response. This immune response may be strictly cellular, leading to a specific T cell response, or it may lead to specific antibody formation. The notion of immunogen should be distinguished from that of antigen, which encompasses both the properties of an immunogen but also that of a substance which cross-reacts immunospecifically with antibodies or immunocytes but is incapable of triggering an immune response. It should also be distinguished from a tolerogen, which is a substance (molecule) inducing immunological tolerance.

Immunogenicity is the capacity to provoke an immune response. When one refers to an immunogenic molecule, this means that this molecule is capable of triggering an immune response by itself, not when conjugated to another macromolecule. Thus, an immunogenic peptide, for example, refers to a peptide immunogenic by itself, whereas a peptide which serves as an important epitope while attached to a macromolecule, should be referred to as immunopotent or, if it is more immunopotent than related peptides, as immunodominant.

A chemical or physical change in a molecule that will result in an increased immune response will increase its immunogenicity, even though it may or may not have changed its antigenic specificity.

The immunogenicity of a substance will depend on the manner in which it is administered, on the amount administered, and on the genetic make-up of the animal or human being immunized. Defining a substance as immunogenic will depend on the sensitivity of the method used to detect the immune response.

See also: Adjuvants; Antibodies, specificity; Antigens; Autoantigens; Cytotoxic T lymphocytes; Immune response; Immune response (Ir) genes; Immunodominance; Immunopotentiation; Tolerance, peripheral; Vaccines.

Further reading

Berzofsky JA and Berkower IJ (1993) Immunogenicity and antigen structure. In: Paul WE (ed) Fundamental Immunology, pp 235-282. New York: Raven Press. Sela M (1969) Antigenicity: some molecular aspects.

Science 166: 1365-1374. Sela M (1973-1987) The Antigens, vols 1-7. London:

Academic Press. Herzenberg LA, Weir DM, Herzenberg LA and Blackwell C (eds) (1997) Handbook of Experimental Immunology, vol 1: Immunochemistry and Molecular Immunology. Oxford: Blackwell Science.

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