Use of tetanus toxoid for testing cell-mediated immunity.

Tetanus toxoid was assessed as a skin test antigen for the measurement of cutaneous delayed-type hypersensitivity (DTH) by comparing the responses to intradermal injections of aqueous tetanus toxoid and an extract of Candida albicans in 50 randomly selected healthy adults and 10 adults with immunodeficiency. Of 42 healthy subjects previously immunised with tetanus toxoid, 33 (79%) reacted to tetanus toxoid and 33 (79%) reacted to Candida albicans. Of eight non-immunised subjects, none reacted to tetanus toxoid although five reacted to Candida albicans. Ten immunodeficient adults previously shown to be anergic to a standard panel of five skin test antigens including Candida albicans, and who had received primary immunisation and booster doses of tetanus toxoid, were anergic on current testing with tetanus toxoid and Candida albicans. Tetanus toxoid in previously immunised subjects has certain advantages as a "recall" DTH test antigen over the standard skin test antigens candidin, mumps, trichophyton, tuberculin and streptokinase-streptodornase used to diagnose cell-mediated immuno-deficiency. It is a sensitive measurement of DTH, it recalls a defined immunological event, it has a low incidence of side effects, and it produces a slight but beneficial boosting of serum antibody to tetanus toxoid.