The effects of an in vitro exposure to 17β-estradiol and nonylphenol on rainbow trout (Oncorhynchus mykiss) peripheral blood leukocytes

While xenoestrogens are routinely detected in the aquatic environment, there is little understanding of the immunotoxicological consequences of exposure to these chemicals in fish, or of the mechanisms through which these effects are mediated. This study was conducted to determine if estrogen receptors (ERs) are present in fish leukocytes and to characterize the effects of 17β-estradiol (E2) and the xenoestrogen nonylphenol (NP) on immune system endpoints in rainbow trout (Oncorhynchus mykiss). Q-PCR was used to confirm that freshly isolated peripheral blood leukocytes (PBLs) express ERs. Following 96-h incubations with E2 or NP (1 nM to 10 μM), PBL ER transcription was again examined using Q-PCR and lipopolysaccharide (LPS)-stimulated proliferation was assessed using flow cytometry. While the transcription of all four forms of rainbow trout ER was unaffected by treatment with E2 or NP, transcription of ERα1 and ERα2 was down-regulated following LPS stimulation. Both E2 and NP, at concentrations of ≥ 100 nM and 10 nM respectively, suppressed leukocyte proliferation. This first report of ERs in rainbow trout PBLs suggests a mechanism through with E2 and other xenoestrogens can modulate immune function. These results highlight the potential for xenoestrogens to impact host resistance to pathogens in wild fish populations.