Effects of pyrethroids on lymphocyte mitogenic responsiveness

The in vitro effects of pyrethroids on the mitogenic responsiveness of murine splenic lymphocytes to concanavalin A (Con A) and lipopolysaccharide (LPS) have been determined. Mitogenic stimulation was measured by uptake of [6-3H]-thymidine. Permethrin and cypermethrin inhibited the mitogenic response to Con A over a concentration range of 1 X 10(-5) M to 5 X 10(-5) M. Relative to these pyrethroids, slightly lower concentrations of fenpropathrin were required to inhibit mitogenic responsiveness to Con A. Fluvalinate was least effective of the pyrethroids tested, and caused mitogenic inhibition at concentrations of 1.5 X 10(-5) M to 5 X 10(-5) M. Unlike the other pyrethroids, concentrations of fluvalinate as high as 1 X 10(-4) M did not result in complete inhibition of the mitogenic response to Con A. Allethrin, was the most potent inhibitor, with effective concentrations in the range of 1 X 10(-6) M to 1.5 X 10(-5) M. Permethrin (3 X 10(-5) M) inhibited the mitogenic response at each of several concentrations of Con A tested, and did not cause a shift in the lymphocyte mitogenic dose-response to Con A. The mitogenic responsiveness to LPS was found to be inhibited by allethrin and permethrin at the same concentrations which inhibited the mitogenesis induced by Con A. The results support the possibility of immune suppression by pyrethroid exposure.