Alg treatment of rhesus monkeys: Attempts to reduce complications by the induction of tolerance

Rhesus monkeys given ultracentrifuged normal horse globulin (NHγ) I.V. prior to antilymphocyte globulin (ALG) treatment became sensitized rather than tolerant to horse globulin, in the majority of cases. The animals’ reactivity to the foreign protein was assessed by measuring antibodies at regular intervals. The possibly enhanced immunosuppressive effect of a standardized ALG course and the severity of localized or generalized complications (presumably attributable to the presence of antibodies) were studied also. A pretreatment course of 4 injections of 10 mg NHγ/kg given on 4 consecutive days during the week prior to ALG treatment led to a degree of tolerance in a few cases; additional immunosuppression with high doses of Imuran did not seem to increase the likelihood of our being able to induce tolerance. The implications of the results, in relation to the current clinical practice of giving NHγ prior to ALG treatment, are discussed.