Lack of immunosuppressive effects of acute and subacute administration of malathion on murine cellular and humoral immune responses

Malathion has been previously shown to cause allergic responses and suppress the generation of a humoral immune response in vivo. In this study, the effect of in vivo administration of malathion on cellular, humoral and mitogenic responses was examined. Acute (50% LD₅₀) or subacute (10% LD₅₀ per day for 14 days) treatment with malathion in vivo did not affect the in vivo generation of specific antibody secreting cells to sheep red blood cells (SRBC) or cytotoxic T lymphocytes (CTL) to allogeneic tumor. However, 5 days following acute administration of malathion, there was a slight increase in humoral immune responsiveness. Acute treatment with 50% LD₅₀ purified malathion did not affect body weight, splenic cell number, or thymus size. However, mitogenic responses to Concanavalin A (Con A) and lipopolysaccharide (LPS) was significantly enhanced on all days tested following acute administration of malathion. In contrast, subacute treatment with malathion did not affect mitogenic response to Con A or LPS, but led to a significant decrease in thymic cell number.