Regulation of the immune response in autoimmune NZB/NZW F1 mice. I. The spontaneous generation of splenic suppressor cells.

The lymphoproliferative responses of rat peripheral blood lymphocytes to phytohemagglutinin (PHA) were studied following treatment with single or multiple doses of cyclophosphamide. A dose-dependent lymphocytopenia was observed with both regimes. The remaining lymphocytes had decreased responses to PHA. Serum collected 24 hr after a single injection of cyclophosphamide and used at a concentration of 5% enhanced the response of cells from normal or cyclophosphamide-treated rats. Serum collected after a course of treatment did not have this effect, but it lacked the marked suppressive activity, at a concentration of 20%, which was shown by normal rat serum. The enhancing activity was not dialysable. Doses of cyclophosphamide adequate to abolish primary antibody production to sheep erythrocytes did not totally abrogate responsiveness to PHA. Thus, the pattern of immunological defects in cyclophosphamide-treated rats consisted of decreased primary antibody production, lymphocytopenia with a decreased response of the remaining lymphocytes to PHA, and diminution of serum suppressive activity.