Effects of pentachlorophenol on innate immunity in an estuarine teleost

Abstract

Nonspecific immune function provides the first defense against potential pathogens; primary cells in this component of immunity are those of phagocytic lineage. Interference with the function of these cells could therefore affect their ability to kill microorganisms, and could ultimately result in decreased resistance to disease. The effects of a model pollutant, pentachlorophenol (PCP), on nonspecific immune functions in an estuarine fish were studied. Macrophages and eosinophils, the two predominate phagocytic cell population in Fundulus heteroclitus, were exposed in vitro and in vivo to environmentally relevant concentrations of PCP. The cells were then assayed in vitro for phagocytosis, the production of reactive oxygen intermediates (ROIs), and bactericidal activity against Listonella anguillarum, a common marine pathogen. Unexposed eosinophils were 2-3 fold more active than macrophages in the production of ROIs and bactericidal activity. Following in vitro exposure to varying concentrations of PCP, both phagocyte populations showed significant decreases in phagocytosis, the production of superoxide {dollar}\rm (O\sb2\sp-),{dollar} and bactericidal activity were significantly inhibited. Two other aspects of ROI-mediated bactericidal activity, hydrogen peroxide {dollar}\rm (H\sb2O\sb2){dollar} production and {dollar}\rm H\sb2O\sb2{dollar}-peroxidase-halide activity, were not significantly changed. Subsequent to these screening studies, Fundulus were exposed in vivo to 50 {dollar}\mu\rm g/l{dollar} PCP for 12 days. A static-renewal system was used for exposures, with water changes every 24 hours. Significant reductions in eosinophil phagocytic activity were produced by this in vivo PCP exposure. Both cell types showed decreased bactericidal activity against Listonella; this was significant in the case of the macrophages. Macrophages and eosinophils from PCP-treated fish also produced significantly increased basal levels of {dollar}\rm O\sb2\sp-{dollar} and {dollar}\rm H\sb2O\sb2{dollar}-peroxidase-halide activity. However, PCP had no effect on the stimulated levels of these ROIs, nor on the stimulated production of {dollar}\rm H\sb2O\sb2.{dollar} These results show that environmentally relevant, sublethal concentrations of PCP can modulate immune function in an aquatic vertebrate, changes which have the potential to negatively affect disease resistance in this and other fish.