The effect of lead and polychlorinated biphenyl exposure on rat natural killer cell cytotoxicity

Splenic natural killer (NK) cell cytotoxicity was assessed in rats chronically exposed to lead (Pb) as lead acetate in the drinking water or polychlorinated biphenyl (PCB) as Aroclor 1254 in the feed. Rats treated with cyclophosphamide were included as positive immunosuppressed controls. Weanling, male Sprague-Dawley rats exposed to 50 and 500 ppm PCB in the feed for ten weeks exhibited significantly suppressed (P less than 0.01) splenic NK activity. Cyclophosphamide injected i.p. six days prior to termination at a dose of 75 mg/kg also significantly inhibited splenic NK activity. NK cell activity was reduced, though not significantly, in spleen cells isolated from animals exposed to 10 and 1000 ppm Pb as Pb acetate in the drinking water for ten weeks. In vitro exposure of rat spleen cells to PCB at concentrations of 0.4 and 20.0 micrograms/ml similarly resulted in a significant depression of splenic NK cell activity. In addition, in vitro exposure to lead at the same concentrations resulted in suppressed NK cell cytotoxicity of rat splenocytes. These results indicate that two environmental contaminants have the ability to adversely affect NK cell cytotoxicity. The effects seen here with Pb and PCB on NK cells may in part explain the tumor inducing effect these chemicals are suspected of possessing via compromising the immune surveillance system.