Cyclophosphamide-induced suppressor cells in mice: suppression of the antibody response in vitro and characterization of the effector cells.

It was found earlier that nonspecific suppressor cells obtained from the spleen of mice injected with cyclophosphamide (Cy) at a dose of 200 mg/kg body wt are nonadherent, surface Ig negative, and Thy-1 negative. It is now reported that Cy-induced suppressor (Cy-S) cells suppress the in vitro primary and secondary humoral responses in a dose-dependent manner. Suppressor activity is a property of a low density cell that is found in the spleen from 5 to 11 days after Cy administration. Cy-S cells are negative for a number of T-cell markers and are nonadherent to plastic. They are not agglutinated by peanut agglutinin and do not acquire the Thy-1 antigen after treatment with thymosin, suggesting that they are not T-cell precursors. While NK activity was detected in the Cy-S cell preparations, this activity was removed by treatment with antibodies specific for the Qa-5 antigen and complement without affecting the suppressor activity. Cy-S cells are, therefore, distinct from B cells, T cells, NK cells, and macrophages.