Organophosphorus pesticide immunotoxicity: effects of O,O,S-trimethyl phosphorothioate on cellular and humoral immune response systems

The time course of immunosuppression induced by acute treatment with O,O,S-trimethyl phosphorothioate (OOS-TMP), an impurity in technical formulations of malathion, was examined in female C57B1/6 mice. Both cell-mediated and humoral immune responses were examined and included allospecific cytotoxic T cells, proliferative response to mitogens, interleukin-2 production and antibody production to sheep red blood cells. OOS-TMP pretreatment led to a reversible suppression of the generation of cytotoxic T lymphocytes and antibody-secreting cells to sheep erythrocytes. However, the mitogenic response of splenocytes from animals treated with nontoxic doses of OOS-TMP (as measured by body weight loss, serum cholinesterase levels and splenic lymphocyte number) to concanavalin A was not significantly suppressed, but the response to the B cell mitogen lipopolysaccharide was slightly decreased on day 1 following treatment. In contrast, interleukin-2 production was elevated by 24 h following treatment, but had returned to control levels by day 7. These data suggest that OOS-TMP was able to block the generation of cytotoxic T lymphocytes and antibody responses at doses of OOS-TMP that did not affect body weight or splenic lymphocyte number and this suppression was reversible.