T cell rosette formation in primates, pigs, and guinea pigs. The influence of immunosuppresive agents

Out of 144 combinations of lymphocytes from 8 species and erythrocytes from 18, significant numbers of rosettes were found in only 14. Human and chimpanzee lymphocytes formed rosettes in the greatest number of combinations (5), pig lymphocytes with 3, and guinea pig lymphocytes with only one erythrocyte (rabbit). In all positive combinations tested, the percentage of rosette-forming cells was highest in the thymus, intermediate with lymph node and peripheral blood lymphocytes, and lowest in the spleen. Using the guinea pig rosette-forming cell as an experimental test for T lymphocytes, the effect of several immunosuppressive drugs on the percentage of lymphocytes that are T cells was measured. Cyclophosphamide injected into guinea pigs increased this percentage the most, cortisone and tilorone increased the percentage of rosette-forming cells slightly, and azathioprine and vinblastine caused no change. After in vitro incubation with the lymphocytes, cyclophosphamide, azathioprine, and tilorone increased the percentage of rosette-forming cells and vinblastine reduced this percentage.