Bisphenol A (BPA) is a well-known endocrine disrupting chemical (EDC), ubiquitous
in the aquatic environment, which poses an ecotoxicological risk to the health of
aquatic organisms. However, the immunotoxic effects of its long-term exposure on fish
have received limited attention. We examined a number of typical immune-related parameters
and oxidative stress indices in the liver and blood serum of the red common carp (Cyprinus
carpio), following a 30-day exposure to five different concentrations of BPA (0.1,
1, 10, 100, and 1000μg/L). A significant increase in the hepato somatic index was
observed in fish upon exposure to 1000µg/L BPA, which correlated strongly with the
accumulated BPA concentrations in fish bile. Induced oxidative stress was also apparent
in the exposed fish liver, based on the enhanced levels of lipid peroxidation and
inhibited activities of catalase, superoxide dismutase, and glutathione peroxidase.
Serum lysozyme and C-reaction protein levels increased at low concentrations of exposure;
however, they were significantly suppressed upon exposure to high concentrations.
A significant increase was observed in the levels of immunoglobulin M, complement
component 3, and alkaline phosphatase, in both fish liver and serum at low doses of
0.1 and 1μg/L. This suggests that long-term exposure to environmentally relevant concentrations
of BPA (even as low as 0.1μg/L) could significantly disturb the immune response of
fish. Moreover, RXRα expression in the liver was significantly altered upon BPA exposure
and the trend underlying this change correlated closely with those of the most immune-related
parameters, implying the involvement of the PPARγ/RXRα signaling pathway in regulating
the immune response of fish upon long-term BPA exposure. In short, our results demonstrate
the susceptibility of fish immune system to long-term BPA exposure. Therefore, the
immunotoxicity of EDCs in aquatic organisms should not have been underestimated.