Suppressor T cells in tolerance to deaggregated horse anti-human thymocyte globulin in man

To understand the mechanism by which deaggregated horse anti-human thymocyte globulin (dATG) fails to induce untoward immunological reactions in man, three patients who received ATG and two patients who received dATG were studied for evidence of sensitization or tolerance to the foreign globulin. The ATG but not the dATG recipients developed allergic or serum sickness reactions; antihorse serum antibody could be detected in their serum and their blood cells proliferated in vitro in the presence of horse serum and secreted antihorse serum antibodies (P less than 0.001). Tolerance of the dATG recipients was shown to be mediated by specific T suppressor cells that carry receptors for horse serum and could be detected in the blood of one patient, whom we have studied serially, 13 weeks after therapy. Deaggregated ATG does not induce allergic or serum sickness reactions. It induces tolerance to the foreign protein via the generation of specific short-lived suppressor cells.