Abstract
The effect of experimental long-term azathioprine administration on pre-existing in vitro and in vivo manifestations of delayed hypersensitivity was examined. Adult ewes were administered 3 mg/kg/day azathioprine for periods of up to 28 days. Neither phytohemagglutinin (PHA)-induced nor tuberculin-induced lymphocyte transformation was affected. Similarly, pre-existing skin test positivity to tuberculin showed no observable change following drug therapy. These results agree with the majority of those involving clinical situations and indicate that immunosuppression with azathioprine cannot be effectively monitored by either the lymphocyte transformation response to PHA or by changes in the in vivo or in vitro manifestations of pre-existing delayed cutaneous hypersensitivity.