Effect of administration of malathion for 90 days on macrophage function and mast cell degranulation

Previous studies have shown that acute, oral administration of malathion modulated the humoral immune response to T cell-dependent antigen, mitogenic responses, macrophage function and mast cell degranulation. In this report, the effects of malathion administration for 90 days on macrophage function, as measured by respiratory burst capacity, phagocytic capability and the production of cathepsin D, and mast cell integrity were assessed. A dose-dependent increase in respiratory burst activity was observed at all doses tested. The production of cathepsin D was elevated at doses of 1 mg/kg/day malathion or greater. The phagocytic capability of peritoneal macrophages was elevated at the dose of 0.1 mg/kg/day, but was suppressed at higher doses. The effect of oral administration of malathion for 90 days on the degranulation of mast cells, in both organs (skin and uterus) and peritoneal lavage fluid, was also assessed. Degranulation (both severe and slight) of mast cells from the skin and peritoneum was observed at a dose of 1.0 mg/kg/day or greater. In addition, the percentage of mast cells that were undegranulated was decreased. In the skin, but not the peritoneum, these effects were dose-dependent. In the uterus, the percentage of mast cells that were undegranulated was decreased and severely degranulated was increased at a dose of 0.1 mg/kg/day or greater. These data indicate that repeated administration of malathion increased macrophage function and led to mast cell degranulation at doses as low as 0.1 mg/kg/day for 90 days.