Immunomodulation in adult largemouth bass (Micropterus salmoides) exposed to a model estrogen or mixture of endocrine disrupting contaminants during early gonadal recrudescence

Authors: LEET, JESSICA - Us Geological Survey (USGS); RICHTER, CATHERINE - Us Geological Survey (USGS); CLAUNCH, RACHEL - Us Geological Survey (USGS); GALE, ROBERT - Us Geological Survey (USGS); TILITT, DONALD - Us Geological Survey (USGS); Iwanowicz, Luke

Submitted to: Comparative Immunology Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2024
Publication Date: 2/17/2024
Citation: Leet, J.K., Richter, C.A., Claunch, R.A., Gale, R.W., Tilitt, D.E., Iwanowicz, L.R. 2024. Immunomodulation in adult largemouth bass (Micropterus salmoides) exposed to a model estrogen or mixture of endocrine disrupting contaminants during early gonadal recrudescence. Comparative Immunology Reports. 6 (2024) 200140. https://doi.org/10.1016/j.cirep.2024.200140.
DOI: https://doi.org/10.1016/j.cirep.2024.200140

Interpretive Summary: Environmental estrogens and herbicides are known to adversely affect reproduction in fishes via endocrine disrupting mechanisms. Lesser known are the effects of these aquatic contaminants on immune function. Research here documents that exposure to estrogens or the agricultural herbicide artazine leads to immunomodulation that can be observed months following the cessation of exposure. This has implications beyond reproductive health for fishes exposed to the aquatic contaminants in natural environments of or pond culture operations.

Technical Abstract: Disease outbreaks, skin lesions, fish kill events, and reproductive abnormalities have been observed in wild populations of Centrarchids in watersheds throughout the United States. Occurrence of synthetic and natural hormones from wastewater treatment plants and livestock operations, pesticides from agricultural land use, and phytoestrogens have been implicated as potential causes of these adverse effects. Our objective was to investigate possible immunomodulation in adult largemouth bass (Micropterus salmoides) in response to a seasonal exposure to environmentally relevant contaminants in outdoor experimental ponds. Exposures included 17alpha-ethinylestradiol (EE2; 2.4 ng/L) or a binary mixture of endocrine-active substances commonly detected in surface waters, estrone (E1; 47.9 ng/L)atrazine (5.4 µg/L) and atrazine (ATR; 5.4 µg/L)estrone (47.9 ng/L). The 5-month exposure was conducted from July to December. Functional immune responses of anterior kidney derived leukocytes were evaluated in December at the end of the exposure period, and the following April, 4 four months after dosing ended and just prior to spawning. Concentrations of EE2 and estrone in the mesocosms fell below detectable levels in December, but detectable concentrations of atrazine (2.3 µg/L) persisted at least through May. For each sampling time, anterior kidney leukocytes were isolated and grown in primary culture for the assessment of zymosan-stimulated respiratory burst and lectin-stimulated mitogenic responses. We observed seasonal differences in respiratory burst stimulation over time and treatment with a significantly greater response in April relative to December (Mann-Whitney; P < 0.001). Respiratory burst activity was also significantly greater in April for fish exposed to the binary mixture (atrazine and estrone)E1+ATR relative to control (Kruskal-Wallis One Way on Ranks, Dunn's post hoc vs control; P = 0.008). There were no significant differences in responses between sexes. In April, prior to spawning, we observed a significantly dampened mitogenic response to PHAP (a T cell mitogen) and LPS (a B cell mitogen) in the EE2 treatment relative to control fish. There were no significant differences in responses between sexes for mitogenic response or respiratory burst. However, there was significantly higher alternative complement pathway haemolytic activity in males compared to females in both the control and E1+ATR treatment groups. Our results demonstrate that environmentally relevant concentrations of contaminants can alter immune function in an economically important fish species.