antigens definition
Terminology. 1  Epitope – The distinct surface features of an antigen, its antigenic determinant. 2  Allergen – A substance capable of causing an allergic reaction. 3  Superantigen – A class of antigens that cause non-specific activation of T-cells, resulting in polyclonal T cell activation and massive cytokine release. Also, an antigen is a molecule that binds to Ag-specific receptors, but cannot necessarily induce an immune response in the body by itself. Antigens are usually peptides (amino acid chains), polysaccharides (chains of monosaccharides/simple sugars) or lipids. In immunology, an antigen is a molecule capable of inducing an immune response (to produce an antibody) in the host organism. Sometimes antigens are part of the host itself in an autoimmune disease. Antigens are targeted by antibodies. Each antibody (immune response) is specifically produced by the immune system to match an antigen after cells in the immune system come into contact with it; this allows a precise identification/matching of the antigen and the initiation of a tailored response. The antigen cannot elicit the immune response without the help of an immunologic adjuvant. Similarly, the adjuvant component of vaccines plays an essential role in the activation of the innate immune system. An immunogen is an antigen substance (or adduct) that is able to trigger a humoral (innate) or cell-mediated immune response. Definition noun, plural: antigens Any of the various substances that when recognized as non-self by the adaptive immune system triggers an immune response, stimulating the production of an antibody that specifically reacts with it. Definition. noun, plural: antigens. Any of the various substances that when recognized as non-self by the adaptive immune system triggers an immune response, stimulating the production of an antibody that specifically reacts with it. Supplement Medical Definition of antigen. : any substance (as an immunogen or a hapten) foreign to the body that evokes an immune response either alone or after forming a complex with a larger molecule (as a protein) and that is capable of binding with a product (as an antibody or T cell) of the immune response. In immunology, an antigen is a molecule capable of inducing an immune response in the host organism. Sometimes antigens are part of the host itself in an autoimmune disease. Antigens are targeted by antibodies. Each antibody is specifically produced by the immune system to match an antigen after cells in the immune system come into contact with it; this allows a precise identification or matching of the antigen and the initiation of a tailored response. The antibody is said to match the anti Exogenous antigens are antigens that have entered the body from the outside, for example by inhalation, ingestion or injection. The immune system's response to exogenous antigens is often subclinical. Antigens may be exogenous antigens, endogenous antigens or autoantigens depending on their origin. Word origin: Contraction of antibody-generator. Related forms: antigenic (adjective), antigenically (adverb) See also: allergen, immunogen. Related terms: antigenicity; Blood group antigens; Class i antigens; Class ii antigens; Class iii antigens; Jk antigens; Neoantigen
An antigen is a molecule that binds to Ag-specific receptors, but cannot necessarily induce an immune response in the body by itself.