Immunomodulatory effects of brevetoxin (PbTx-3) upon in vitro exposure in bottlenose dolphins (Tursiops truncatus)

Abstract

Harmful algal blooms (HAB), commonly referred to as ‘red tides’, involving the dinoflagellate Karenia brevis produce a series of neurotoxins known as brevetoxins (PbTx). Brevetoxins have long been associated with extensive fish kills, adverse human health effects such as neurotoxic shellfish poisoning, and have been associated with mortality events in aquatic mammals such as bottlenose dolphins (Tursiops truncatus). The immunotoxicological effects of these brevetoxins have been studied in manatees, humans, and cell lines, however, the effects in bottlenose dolphins remain unclear. There are increasing concerns that dolphins may be exposed to repeated/chronic, sub-lethal concentrations, which may impact their overall health. The objectives of this study were to measure the changes in innate (phagocytosis, respiratory burst, NK cell activity) and adaptive (mitogen-induced B and T lymphocyte proliferation) immune functions upon in vitro exposure to increasing concentrations of brevetoxin (PbTx-3) (0, 0.01, 0.1, 1, 10, 100, 500, and 1000nM) using bottlenose dolphin peripheral blood immune cells. Brevetoxin significantly increased spontaneous lymphocyte proliferation at 0.1–1000nM compared to the unexposed control. Brevetoxin significantly increased T lymphocyte proliferation upon suboptimal (0.1μg/ml) and optimal (1.0μg/ml) Con-A stimulation at 0.01–100nM and 0.1nM of PbTx-3 respectively, as well as suboptimal (0.05μg/ml) and optimal (5.0μg/ml) LPS-induced B lymphocyte proliferation at 0.01–100nM and 0.01–500nM of PbTx-3, respectively. Both neutrophil and monocyte respiratory burst were significantly increased at 500 and 1000nM. There were no significant effects on neutrophil or monocyte phagocytosis or NK cell activity. Importantly, concentrations that modulated immune functions in vitro were within the range measured in the blood of dolphins during two unusual mortality events, suggesting that naturally exposed dolphins may be at risk for immunomodulation. Brevetoxin-induced immunomodulation may increase an animal's susceptibility to bacterial, viral, or fungal infections. Understanding the risk for immunomodulation upon HAB toxin exposure can contribute in the health assessment and management of marine mammals, as well as guide veterinarians and wildlife rehabilitators in caring for and treating afflicted animals.