Effect of chlorpyrifos on immune function in rats

A commercial formulation of chlorpyrifos was evaluated for effects on selec ted immune system functions in male-fisher 344 rats. Chlorpyrifos in an oli ve oil vehicle was administered by oral gavage twice weekly for 28 d at a d ose of 5.0 mg/kg for each treatment. Body weight an;and organ/body weight r atios were unaffected by the chlorpyrifos, In contrast, chlorpyrifos impair ed T-lymphocyte blastogenesis induced by concanavalin A (P = 0.03) and phyt ohemagglutinin (P = 0.023), but did not alter B-lymphocyte blastogenesis in duced by 11 popolysaccharide/dextran (P = 0.082). Humoral immunity (anti-sh eep red blood cell), a T-lymphocyte macrophage-dependent response, was also reduced (P = 0.019) when the antibody response was expressed/10(6) spleen cells,although the response expressed/spleen was unaffected (P = 0.32), ref lecting increased lymphocyte production. The total splenic lymphocyte count s in the chlorpyrifos-treated rats increased by 91% (P < 0.0001), therefore reducing the antibody response when expressed/10(6) spleen cells. Chlorpyr ifos had no effect on macrophage phagocytosis (P = 0.27), but increased the relative percentage expression of CD5+ (P = 0.028) and CD8+ (P = 0.003). T he presence of normal antibody and phagocytic responses in association with reduced T-lymphocyte blastogenesis and enhanced expression of specific cel l surface antigens indicated that chlorpyrifos induced immune alterations a ssociated with lymphocyte subpopulations.