Noun | 1. | antigen - any substance (as a toxin or enzyme) that stimulates an immune response in the body (especially the production of antibodies) substance - a particular kind or species of matter with uniform properties; "shigella is one of the most toxic substances known to man" immunizing agent, immunogen - any substance or organism that provokes an immune response (produces immunity) when introduced into the body immunology - the branch of medical science that studies the body's immune system agglutinogen - any substance that acts as an antigen to cause agglutinin production fetoprotein, foetoprotein - any of several antigens that occur naturally in the fetus and sometimes in adults with cancer anatoxin, toxoid - a bacterial toxin that has been weakened until it is no longer toxic but is strong enough to induce the formation of antibodies and immunity to the specific disease caused by the toxin; "diphtheria toxoid" antigenic determinant, epitope, determinant - the site on the surface of an antigen molecule to which an antibody attaches itself Rh, Rh factor, rhesus factor - a blood group antigen possessed by Rh-positive people; if an Rh-negative person receives a blood transfusion from an Rh-positive person it can result in hemolysis and anemia |