The immunotoxic effects of dual exposure to PCP and TCDD

Pentachlorophenol (PCP) was a commonly used fungicide, herbicide, insecticide, and bactericide in industrial, agricultural, and domestic settings; however, it was also contaminated with polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). It has been reported that technical grade PCP had immunosuppressive effects and that the immune system was the major target of PCDD/PCDFs toxicity. Although the immune response after exposure to PCP or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been studied, the toxic effects of exposure to both PCP and TCDD have not yet been reported. The aim of this study was to evaluate the effects on immune cells from mice intraperitoneally immunized with OVA and subsequently treated with PCP or TCDD alone or in combination by gavage. The animals were terminated on day 7 and 14, and the spleen and plasma samples were collected for immunotoxicity evaluation. The numbers and populations of splenocytes, T cell-derived cytokines produced by splenocytes, splenocyte-generated cytotoxicity and OVA-specific antibodies in plasma were investigated. Our results indicate that the spleen/body weight ratio and splenocyte number was reduced by TCDD alone; in addition, this reduction was enhanced when TCDD was combined with PCP. Exposure to TCDD alone or in conjunction with PCP suppressed many ovalbumin (OVA)-stimulated cytokines, including IL-2, IFN-γ, IL-4, IL-5, and IL-10. Furthermore, the immunoglobulins IgG and IgM were suppressed in mice administered by PCP alone, but the suppressive effects were greater in mice treated with TCDD alone or in combination with PCP. Co-exposure to PCP and TCDD resulted in an antagonistic effect on TCDD-induced suppression of IFN-γ and IL-10. Our results demonstrate that PCP alone is immunotoxic, regardless of the presence of TCDD. PCP led to mild changes in cytokine secretion, and it compromised splenocyte-generated cytotoxicity and IgM and IgG antibody production on day 7. The finding that PCP antagonizes TCDD-induced IFN-γ suppression could be due to the competitive binding of PCP to AhR (aryl hydrocarbon receptor).