superantigen, one of a family of related substances, including staphylococcal and streptococcal exotoxins, that can short-circuit the normal sequence of events leading to activation of helper T cells. Superantigens initiate an uncontrolled proliferation of T cells but do not require processing and presentation by macrophages. The result is either an acute and potentially life-threatening disease, such as toxic shock syndrome, or a chronic inflammatory process, such as rheumatic fever.
