Antigen is a virus, bacterium, or other foreign substance in the body that triggers an immune response. The body forms a protein substance called an antibody in response to a specific antigen. The antibody reacts with or neutralizes that antigen. Antigens also include toxins and foreign blood cells.
The effects of antigens on the body vary. In some cases, when foreign antigens enter the body, the body produces enough antibodies to prevent symptoms from developing. In other cases, the body does not manufacture enough antibodies to prevent symptoms, but the antibodies help the victim recover. Individuals respond to antigens differently. For example, the immune systems of most people are not affected by pollen. But in people who suffer an allergy known as hay fever, pollen acts as an antigen and triggers an immune response. The body can produce a great number of different antibodies that attack specific antigens.
See also Immune system .
