Antigens are substances that stimulate the production of antibodies in the body. They can be found on the surface of microorganisms or other foreign substances that enter the body. Synonyms for the word antigens include immunogens, agglutinogens, and epitopes. Immunogens are substances that trigger an immune response in the body. Agglutinogens are antigens that can cause clumping of red blood cells. Epitopes are specific regions on an antigen that are recognized by antibodies. Other related terms include haptens, which are small molecules that can become antigens when combined with larger proteins, and superantigens, which can cause an extreme immune response. Understanding these synonyms can help in the study of immunology and the development of vaccines.