Certain types of antigens that activate a large proportion of an organism’s immune system T cells. These superantigens, which thus over-activate the organism’s immune system, are thought to be responsible for some autoimmune diseases (in which T cells attack and destroy the organism’s own, healthy tissues).
An antigen that binds with class 1 major histocompatibility antigens and T-cell receptors and causes the simultaneous activation of large numbers of T cells and massive release of cytokines. Such antigens do not have to be processed by macrophages to be recognized by T cells. Exotoxins from bacteria such as staphylococci and group A streptococci act as superantigens. A superantigen known as toxic shock syndrome toxin-I causes toxic shock syndrome.