Mercury-Modulated Immune Responses in Arctic Barnacle Goslings (Branta leucopsis) upon a Viral-Like Immune Challenge

Historical mining activities in Svalbard (79 degrees N/12 degrees E) have caused local mercury (Hg) contamination. To address the potential immunomodulatory effects of environmental Hg on Arctic organisms, we collected newborn barnacle goslings (Branta leucopsis) and herded them in either a control or mining site, differing in Hg levels. An additional group at the mining site was exposed to extra inorganic Hg(II) via supplementary feed. Hepatic total Hg concentrations differed significantly between the control (0.011 +/- 0.002 mg/kg dw), mine (0.043 +/- 0.011 mg/kg dw), and supplementary feed (0.713 +/- 0.137 mg/kg dw) gosling groups (average +/- standard deviation). Upon immune challenge with double-stranded RNA (dsRNA) injection, endpoints for immune responses and oxidative stress were measured after 24 h. Our results indicated that Hg exposure modulated the immune responses in Arctic barnacle goslings upon a viral-like immune challenge. Increased exposure to both environmental as well as supplemental Hg reduced the level of natural antibodies, suggesting impaired humoral immunity. Hg exposure upregulated the expression of proinflammatory genes in the spleen, including inducible nitric oxide synthase (iNOS) and interleukin 18 (IL18), suggesting Hg-induced inflammatory effects. Exposure to Hg also oxidized glutathione (GSH) to glutathione disulfide (GSSG); however, goslings were capable of maintaining the redox balance by de novo synthesis of GSH. These adverse effects on the immune responses indicated that even exposure to low, environmentally relevant levels of Hg might affect immune competence at the individual level and might even increase the susceptibility of the population to infections.

Automated summary

Historical mining activities in Svalbard have led to mercury contamination, which can affect the immune responses of Arctic organisms. In this study, newborn barnacle goslings were raised in control or mining sites with different levels of mercury. Results showed that exposure to mercury modulated the immune responses in barnacle goslings. Increased exposure to both environmental and supplemental mercury reduced natural antibodies and upregulated the expression of proinflammatory genes. These adverse effects on immune responses suggest that even low, environmentally relevant levels of mercury can impact immune competence and increase susceptibility to infections at the individual and population levels.