Antigen
a foreign substance in the body (a bacterium, virus, or protein, for example) that can cause disease â and whose presence triggers an immune response (the formation of antibodies).
Description: Substance (such as a virus or bacterium) that triggers an immune system response in the form of antibodies.Source: Specialized encyclopedia and dictionariesDescription: A foreign substance that elicits the production of antibodies.Source: Specialized encyclopedia and dictionaries
Any macromolecule that triggers an immune response. Antigenicity depends on the ability of the peptide fragments to be presented by the MHC molecules.