antigen

/ˈæntəʤən/

Other forms: antigens

An antigen is a substance that your immune system reacts against. A harmful virus is one kind of antigen.

When your immune system detects some toxic foreign body or substance, it sends up defenses against this antigen called antibodies. This ability of your body, to protect you against bacteria and other antigens, helps keep you healthy. Antigen comes from a French word, antigène, from Greek root anti-, "against, and the word-forming suffix -gen, "thing that produces or causes."

Definitions of antigen

1. noun

   any substance (as a toxin or enzyme) that stimulates an immune response in the body (especially the production of antibodies)
   types:

   immunizing agent, immunogen

   any substance or organism that provokes an immune response (produces immunity) when introduced into the body

   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

   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

   vaccine, vaccinum

   immunogen consisting of a suspension of weakened or dead pathogenic cells injected in order to stimulate the production of antibodies

   toxin antitoxin

   a mixture of toxin and antitoxin used to immunize against a disease

   isoagglutinogen

   an antigen capable of causing the production of (or reacting with) an isoagglutinin

   AFP, alpha fetoprotein, alpha foetoprotein

   an abnormally large amount of this fetoprotein in the fetus can signal an abnormality of the neural tube (as spina bifida or anencephaly)

   type of:

   substance

   a particular kind or species of matter with uniform properties