Abstract

Certain species of the marine diatom Psuedo-nitzschia produce the toxin domoic acid (DA), which biomagnifies in the food web and can adversely affect marine mammals. DA blooms have resulted in stranding and mortality events involving California sea lions and Southern sea otters. While the neurotoxic effects of DA exposure are relatively well understood, the sub-lethal, immunotoxic effects have not been investigated in marine mammals. This is especially important, as the immune system is an important interface between an individual's health and the pathogens present in its environment. It was recently demonstrated in our laboratory for the first time in a mammalian species that in vitro exposure to DA significantly decreased mouse leukocyte phagocytosis, while no effects were observed for ConA-induced T lymphocyte proliferation. In vitro immune assays were utilized to evaluate both innate (phagocytosis, respiratory burst) and acquired (mitogen-induced B and T lymphocyte proliferation) immune functions in healthy California sea lions and Southern sea otters. The direct effects of DA on peripheral blood leukocytes (neutrophils and monocytes for phagocytosis and respiratory burst, mononuclear cells for lymphocyte proliferation) were performed using increasing concentrations of DA (0, 0.0001, 0.001, 0.01, 0.1, 1.0, 10, and 100 µM). These concentrations are within the range of those measured in the serum of naturally exposed California sea lions. The results to date show that for California sea lions, (1) DA does not significantly modulate phagocytosis or the respiratory burst, (2) DA significantly increases ConA-induced T lymphocyte proliferation at 0.001, 0.01, 0.1 and 1.0 µM, and (3) that mice failed to predict the immunotoxic effects of DA in California sea lions upon in vitro exposure. Sea otter data has insufficient statistical power to date. Understanding the risk for immunotoxicity upon DA exposure will contribute in the health assessment and management of Southern sea otters and California sea lions, as well as guide veterinarians and wildlife rehabilitators in caring for and treating afflicted animals.

Acknowledgements

This work was supported by a grant from the Morris Animal Foundation.