Immunotoxicity of pentachlorophenol (PCP): Increased susceptibility to tumor growth in adult mice fed technical PCP-contaminated diets

Adult male C57B1 6 mice were fed diets containing 50 or 500 ppm pure (99+%) or technical grade (86%) pentachlorophenol (PCP) for 10-12 weeks prior to assessment of immunocompetence. Assays for immunocompetence included in vivo host susceptibility to virus infection and tumor growth and in vitro quantitation of T-cell cytotoxicity and macrophage phagocytosis. Exposure of mice to technical PCP resulted in profound enhancement of tumor susceptibility. The incidence of progressive methylcholanthrene (MCA)-induced transplanted tumors increased from 35% in controls to 67 and 82% in animals exposed to 50 and 500 ppm technical PCP, respectively. Mortality following primary Moloney sarcoma virus (MSV) inoculation and secondary MSB challenge increased from 19% in controls to 45 and 73% in animals exposed to 50 and 500 ppm technical PCP, respectively. An additional 50% of the MSV MSB challenged mice exposed to 50 ppm technical PCP exhibited tumor dissemination in the spleen. Animals exposed to pure PCP did not exhibit enhancement of primary MCA- or MSV-induced tumor growth. However, splenic tumor development was observed in 22 and 44% of the MSV MSB challenged mice exposed to 50 and 500 ppm pure PCP, respectively. Control mice did not develop splenic tumors. In contrast to the enhancement of tumor susceptibility, mortality associated with encephalomyocarditis virus infection tended to be reduced by technical PCP exposure. In vitro immune functional assessment indicated significant depression in T-cell cytolytic activity and enhancement of macrophage phagocytosis in animals exposed to technical PCP. No significant changes in in vitro immune response were noted with cells from pure PCP-exposed animals.