Factors which Determine Immunogenicity

Immunogenicity is the ability to induce a humoral and/or cell mediated immune response. Although a substance that induces a specific immune response is usually called an “antigen” the more proper term is an “immunogen.” Antigencity is the ability of an antigen simply to interact specifically with free antibody and/or with antigen binding receptors on lymphocytes. Although all molecules possessing the property of immunogenicity also possess the property of antigenicity, the reverse is not true. Some small molecules called haptens possess the property of antigenicity but are not capable by themselves of inducing a specific immune response.

Factors which influence immunogenicity include the following:

(1) composition and size: (see outline)

(2) Conformation: See right hand panel

(3) foreignness: In order to elicit an immune response, a molecule must be recognized as nonself. The ability to recognize self molecules is thought to arise during development by exposure of immature lymphoctyes to self-components. Any molecule that is not exposed to immature lymphoctyes during this critical period is later recognized as nonself, or foreign, by the immune system.

(4) dose and route: (see outline)

(5) genotype of an immunized animal also influences the type of immune response the animal manifests. MHC gene products which function to present processed antigen to T cells play a central role in this variety. The response of an animal is also influenced by the genes that encode B-cell and T-cell receptors and by genes that encode various proteins involved in immune regulatory mechanisms. Genetic variability in all of these genes affects the immunogenicity of a given macromolecule in different animals.