Investigations into the mechanism of immunosuppression caused by acute treatment with O,O,S-trimethyl phosphorothioate. I. Characterization of the immune cell population affected.

Acute administration of O,O,S-trimethyl phosphorothioate (OOS-TMP), an impurity in technical formulations of malathion, to female C57B1/6 mice was previously shown to suppress the generation of both cytotoxic T lymphocyte to alloantigen and antibody-secreting cells to sheep red blood cells. In this report, macrophages were shown to be the immune cell population most affected by acute OOS-TMP pretreatment by cell separation and reconstitution experiments. Macrophages from OOS-TMP-treated animals had increased levels of nonspecific esterases. In addition, the size distribution of macrophages from treated animals was slightly larger and more heterogeneous than macrophages from control animals. However, macrophages from OOS-TMP-treated animals did not exhibit tumoricidal activity. These data suggest that macrophages from OOS-TMP-treated animals were similar to those located in nonimmune inflammatory sites.