Mechanisms of Immunosuppression: Effects of Cyclophosphamide on Cellular Immunity

Abstract

Abstract A course of cyclophosphamide administered to guinea pigs after immunization with mycobacteria led to a transient inhibition of cutaneous hypersensitivity to tuberculin protein. This treatment resulted in generalized depletion of lymphoid cells, including lymphopenia, and a substantial reduction in the number of macrophages found in induced peritoneal exudates. Results of in vivo cell transfer studies indicated that cyclophosphamide-treated recipients were rendered transiently unresponsive to purified tuberculin protein (PPD). However, sensitized lymph node cells from drug-treated donors were capable of transferring immunity to normal recipients. In vitro tests of cellular immunity with lymph node cells from drug-treated animals yielded discordant results. The proliferative response to both PHA and PPD was significantly impaired. However, these lymphoid cells functioned normally in assays for migration inhibition factor (MIF). Thus, these data suggest that cyclophosphamide can limit proliferation without impairing intermitotic functions of sensitized lymphocytes, such as the release of MIF. Results of this study suggest that cyclophosphamide does not impair development of a population of specifically sensitized T-type lymphocytes. However, several components of the expression phase are affected; the resultant anergy is probably due to a summation of effects on lymphocytes and macrophages.