immunogens

An immunogen is any substance that can provoke an adaptive immune response and generate immunological memory. In many contexts immunogen is used to mean a component that will stimulate B or T cells, while the broader term antigen refers to any substance that can be recognized by the immune system. Not all antigens are immunogenic in every context; some may be tolerated or require specific conditions to elicit a response.

Immunogenicity depends on multiple factors. Larger, complex, and foreign molecules are more likely to be immunogenic. The route of exposure, dose, and the presence of adjuvants or other inflammatory signals influence the strength of the response. The host’s genetic background and prior exposure history also play important roles. Some substances, such as self-antigens, are typically non-immunogenic due to tolerance, while small molecules called haptens become immunogenic only when linked to a carrier protein.

Mechanisms of immunogenicity involve antigen presentation and lymphocyte activation. B cells recognize specific epitopes and can produce antibodies, while T cells require peptide presentation on MHC molecules to become activated. Helper T cells aid B and cytotoxic T cell responses, leading to clonal expansion and the formation of memory cells for faster responses upon re-exposure.

Clinical and practical relevance includes vaccines that use immunogenic antigens to confer protection, the use of adjuvants to boost responses, and considerations of immunogenicity in biotherapeutics, autoimmunity, and allergies. Haptens, autoantigens, and allergens illustrate the spectrum of immunogenic substances encountered in medicine.