immunogén

An immunogen, or immunogenic substance, is a molecule or a part of a molecule capable of eliciting an adaptive immune response in a host. Immunogens can trigger the activation of B cells to produce antibodies and T cells to mount cellular responses, ultimately contributing to immunity or protection against a pathogen. All immunogens are antigens in the sense that they contain recognizable epitopes, but not all antigens are immunogens. Some substances bind to antibodies or receptors without provoking a response; small molecules called haptens are classical examples that become immunogenic only when attached to a larger carrier protein.

Immunogenicity depends on multiple factors. Molecular size and complexity, foreignness to the host, the number and accessibility of epitopes, and the stability of the antigen influence the strength of the response. The inflammatory context, exposure route, and presence of adjuvants or delivery systems can dramatically enhance immunogenicity by providing necessary costimulatory signals. Self-antigens are typically poorly immunogenic due to immune tolerance, although certain conditions can break tolerance and contribute to autoimmunity.

Common immunogens include proteins, polysaccharides, and some nucleic acids. In research and medicine, proteins such as keyhole limpet hemocyanin (KLH) and ovalbumin are frequently used as model immunogens to study immune responses. In vaccines, the immunogenic component is selected to induce durable protection, often with adjuvants to boost the response.

Evaluation of immunogenicity involves measuring specific antibody production, T-cell responses, and functional outcomes such as neutralization or cytotoxic activity.