Age-related differences in the sensitivity of the fish immune response to a coplanar PCB

Polychlorinated biphenyls (PCBs) are widespread environmental pollutants. Because of their persistence and bioaccumulation in aquatic organisms (among other factors), the biological impact of PCB exposure on resident fish populations is of particular concern. To assess the effect(s) of an environmentally relevant coplanar PCB congener on the fish immune response, juvenile and aged Japanese medaka (Oryzias latipes) were injected i.p. with either vehicle or PCB 126 (at 0.01 or 1.0 μg/g BW) and examined after 3 and 14 days. CYP1A protein levels, examined as an indicator of PCB exposure, were significantly increased (compared to controls) in all fish treated with the highest PCB dose. Kidney phagocyte superoxide (O₂^•-) production was examined to indicate effects upon innate immune function. After 14 days, unstimulated O₂^•- production by kidney phagocytes from juvenile and aged medaka treated with the highest PCB dose was significantly increased compared to controls. Stimulated O₂^•- production by aged PCB-treated fish was unaffected (compared to controls) at both post-exposure timepoints. However, phagocytes from PCB-treated juvenile medaka demonstrated reduced O₂^•- production at 3 days post-exposure and increased levels after 14 days (compared to controls). These results demonstrate the sensitivity of medaka phagocyte function for examining PCB-induced immunotoxicity.