Kinetics of the reactive cell clones after immunosuppression and induction of tolerance: (1) inhibition of 19 S and 7 S plaque-forming cells in the primary and secondary immune response to sheep red blood cells by cyclophosphamide and 036.5122 (Asta).

The kinetics of the reactive cell clones after primary and secondary immunization with SRBC1) modified by cyclophosphamide and a newly synthesized cyclophosphamide analogue 036.5122 (Asta), have been studied. After primary immunization, both substances caused a severe and dose dependent depletion of 19 S PFC2). The 7 S PFC in the late primary response were only slightly inhibited by cyclophosphamide in low dose ranges, indicating, that sensitization could not be prevented by this substance. In contrast, 0.36.5122 was fully able to suppress 7 S PFC. Thus, treatment with 0.36.5122 after primary immunization can fully prevent the expression of the specific response. Experiments dealing with inhibition of a secondary immune response revealed that both test substances were able to strongly suppress the 19 S as well as the 7 S PFC. In general, 036.5122 demonstrates a higher suppressive potency, and the timing of its application for optimal suppression is less delicate than that of cyclophosphamide. 036.5122 was equally well inhibitory, whether given directly before or after antigenic challenge. The hypothesis is discussed, whether the immunosuppressive effect of 036.5122 given before antigenic challenge in the secondary immune response is due to cytotoxic damage of antigen reactive clones stimulated by persisting antigen.