Regional variations and relationships among cytokine profiles, white blood cell counts, and blood mercury concentrations in Steller sea lion (Eumetopias jubatus) pups

The Steller sea lion (SSL) populationwest of 144 degrees Wlongitude experienced a significant population decline. While there appears to be a stable or increasing population trend in rookeries in the Gulf of Alaska (GOA) and Southeast Alaska (SEA), some rookeries within the Aleutian Islands (AI) have failed to recover. Previous studies found regional differences in whole blood total mercury concentrations ([THg]) showing more than 20% of AI pups had [THg] above critical thresholds for increased risk of immunological effects and other adverse outcomes. Measurements of immune cell-signaling proteins can be used to evaluate the immune status ofmarinemammals in relation to [THg]. We compared serum cytokine and chemokine concentrations in pups among regions (AI, eastern GOA, SEA), and examined associations among cytokines, chemokines, white blood cell (WBC) counts, and [THg]. Considering liver is an important target organ formercury and immune protein synthesis we additionally examined the relationship of [THg] with liver-related enzymes serum aspartate (AST) and alanine aminotransferase (ALT). We observed regional differences in cytokine and chemokine measurements and immune protein associations. There was a positive association between totalWBC counts and [THg] in AI pups, whereas a negative association between lymphocytes and [THg] in SEA pups. These findings may indicate regional variation in proliferation and differentiation of hematopoietic cells, differences in immune systemdevelopment, and/or a difference in antigenic stimuli. No associations between [THg] and cytokines, chemokines, AST or ALT were found. Observed regional differences in cytokine and chemokine milieu during gestational and early development in SSL pups could lead to an imbalance in cell differentiation that could impact immunological resiliency in juvenile and adult life stages. We report concentration ranges of a suite of cytokines and chemokines whichmay prove to be a useful metric for ecotoxicology and risk assessment studies in SSLs and other wildlife. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The Steller sea lion population west of 144 degrees W longitude has experienced a significant decline, with some rookeries in the Aleutian Islands failing to recover. Differences in immune cell signaling proteins and mercury concentrations were found among regions, suggesting potential impacts on immune status in pups. Regional variations in cytokine and chemokine measurements were observed, indicating potential differences in immune system development and hematopoietic cell differentiation. No direct associations were found between mercury concentrations and immune proteins or liver-related enzymes. These findings highlight the importance of considering regional differences in immune factors and mercury exposure for ecological and risk assessment studies in Steller sea lions and other wildlife.