Eosinophilia and biotoxin exposure in bottlenose dolphins (Tursiops truncatus) from a coastal area impacted by repeated mortality events.

Bottlenose dolphins (Tursiops truncatus) inhabiting coastal waters in the northern Gulf of Mexico have been impacted by recurrent unusual mortality events over the past few decades. Several of these mortality events along the Florida panhandle have been tentatively attributed to poisoning from brevetoxin produced by the dinoflagellate Karenia brevis. While dolphins in other regions of the Florida coast are often exposed to K. brevis blooms, large-scale dolphin mortality events are relatively rare and the frequency and magnitude of die-offs along the Panhandle raise concern for the apparent vulnerability of dolphins in this region. We report results from dolphin health assessments conducted near St. Joseph Bay, Florida, an area impacted by 3 unusual die-offs within a 7-year time span. An eosinophilia syndrome, manifested as an elevated blood eosinophil count without obvious cause, was observed in 23% of sampled dolphins. Elevated eosinophil counts were associated with decreased T-lymphocyte proliferation and increased neutrophil phagocytosis. In addition, indication of chronic low-level exposure to another algal toxin, domoic acid produced by the diatom Pseudo-nitzschia spp., was determined. Previous studies of other marine mammal populations exposed recurrently to Pseudo-nitzschia blooms have suggested a possible link between the eosinophilia and domoic acid exposure. While the chronic eosinophilia syndrome could over the long-term produce organ damage and alter immunological status and thereby increase vulnerability to other challenges, the significance of the high prevalence of the syndrome to the observed mortality events in the St. Joseph Bay area is unclear. Nonetheless, the unusual immunological findings and concurrent evidence of domoic acid exposure in this sentinel marine species suggest a need for further investigation to elucidate potential links between chronic, low-level exposure to algal toxins and immune health.

Immunomodulatory effects of domoic acid differ between in vivo and in vitro exposure in mice.

The immunotoxic potential of domoic acid (DA), a well-characterized neurotoxin, has not been fully investigated. Phagocytosis and lymphocyte proliferation were evaluated following in vitro and in vivo exposure to assay direct vs indirect effects. Mice were injected intraperitoneally with a single dose of DA (2.5 microg/g b.w.) and sampled after 12, 24, or 48 hr. In a separate experiment, leukocytes and splenocytes were exposed in vitro to 0, 1, 10, or 100 microM DA. In vivo exposure resulted in a significant increase in monocyte phagocytosis (12-hr), a significant decrease in neutrophil phagocytosis (24-hr), a significant decrease in monocyte phagocytosis (48-hr), and a significant reduction in T-cell mitogen-induced lymphocyte proliferation (24-hr). In vitro exposure significantly reduced neutrophil and monocyte phagocytosis at 1 muM. B- and T-cell mitogen-induced lymphocyte proliferation were both significantly increased at 1 and 10 microM, and significantly decreased at 100 microM. Differences between in vitro and in vivo results suggest that DA may exert its immunotoxic effects both directly and indirectly. Modulation of cytosolic calcium suggests that DA exerts its effects through ionotropic glutamate subtype surface receptors at least on monocytes. This study is the first to identify DA as an immunotoxic chemical in a mammalian species.

Immunomodulatory effects of organochlorine mixtures upon in vitro exposure of peripheral blood leukocytes differ between free-ranging and captive southern sea otters (Enhydra lutris).

Organochlorines (OCs), notably polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are ubiquitous environmental contaminants. Contaminant-induced immunosuppression by OCs has been implicated as a co-factor in the deaths of thousands of marine mammals in infectious disease epizootics over the last two decades, and limited studies support the hypothesis that PCBs are immunomodulatory. This study represented a unique opportunity to assess the potential differences in susceptibility to OCs between captive and free-ranging sea otters originating from the same genetic population. In vitro immune assays were utilized to evaluate both innate (phagocytosis and respiratory burst) and acquired (mitogen-induced B and T lymphocyte proliferation) immune functions. Individual PCBs (138, 153, 169 and 180) as well as TCDD and all 26 possible combinations were tested. Mixtures were tested as they represent 'real life' exposure. Our results suggest that (1) different immune functions were sensitive to different OC mixtures in both magnitude and direction (enhancement/suppression) and (2) differences in sensitivities upon in vitro exposure to OCs occurred between free-ranging and captive otters. Differences in susceptibility could be explained by the acute stress of capture, the chronic stress of captivity or nutritional differences. Understanding differences in toxicity to different populations of sea otters will have important implications for risk assessment as well as conservation and management strategies.