The preparation and immunosuppressive properties of equine antihuman thymocyte membrane immunoglobulin G.

Human thymocytes separated by a Ficoll gradient produced a cell population that was 99% pure thymocytes and free of platelets, leukocytes, and epithelial cells. These cells, disrupted by a nitrogen bomb, produced a membrane-ribosome antigen fraction confirmed by enzyme analysis. Equine antithymocyte membrane-immunoglobulin G (ATM-IgC) prepared against this antigen in four of five horses contained immunosuppressive properties capable of prolonging monkey skin allograft survival longer than 21 days. No adverse effects were noted by the intramuscular and intravenous administration of this antisera to primates, and autopsy examination showed marked depletion of paracortical lymphocytes in the spleen and mesenteric lymph nodes. A moderate thrombocytopenia occurred during a 4 hour intravenous administration of ATM-IgG to primates with a marked decrease in the peripheral lymphocyte count. The deposition of ATM-IgG upon monkey glomerular basement membrane could not be demonstrated by immunofluorescent techniques. The specificity of this globulin to contain anti-T-cell antibody was confirmed by an immunofluorescent assay in that ATM-IgG reacted with both human thymocytes and peripheral blood thymus-dependent cells, but was nonreactive when tested against a panel of human cells free of thymus-dependent antigens.