Impacts of PCBs on grey seal pup immunity and influenza A infection vary across biological scales.

Disease outbreaks in marine species have increased, prompting concern regarding the health of coastal ecosystems. Environmental contaminants are hypothesized to contribute to disease outbreaks, as many contaminants have documented immunosuppressive effects in a variety of marine organisms. Of particular concern are marine mammals that have long life-spans, live in coastal waters, and have thick blubber, all of which leads to greater contaminant exposure and accumulation. In the Northwest Atlantic Ocean, polychlorinated biphenyls (PCBs) have been detected in grey seals (Halichoerus grypus), yet research on impacts of PCBs in this species is limited or yields contradictory results. We first validated the use of dried blood spot (DBS) cards to measure contaminants in wild grey seal pups using a paired analysis to whole blood samples (N = 30). Then, DBS was used to measure PCBs in pup blood (N = 127) and we assessed the impact of PCBs on gene expression (N = 23), cytokines (N = 87), and influenza A virus (IAV) infection status (N = 127). We found a significant correlation between the concentrations of PCBs detected by DBS and whole blood. PCBs were found to down-regulate adaptive immunity genes, but up-regulate innate immunity and defense response genes. Despite the apparent effects of PCBs at the molecular level, we observed no difference in cytokine profiles nor IAV infection status across pups with and without measurable PCBs. Our research highlights the intricacies of contaminant-induced effects on immune function and sheds light on how grey seals survive ongoing threats in their environment.