Abstract

Over the last several decades, the frequency and global distribution of harmful algal blooms (HAB) incidents appear to have increased. This increase in HAB events may be related to human activity, such as increased pollution runoff into aquatic ecosystems or global warming. Exposure to two HAB toxins, brevetoxin and domoic acid (DA), produced by the dinoflagellate Karenia brevis and marine diatom Pseudo-nitzschia, respectively, has resulted in adverse health effects in marine mammals. Biotoxin-induced immunomodulation may increase an individual's susceptibility to a variety of bacterial, viral, protozoal, or fungal pathogens. Dolphins may be exposed to sublethal (acute, subacute, and chronic) low-dose concentrations of brevetoxin and DA, which may impact their overall health and may contribute to unusual mortality events and stranding events. This project is testing the following hypothesis, "In vitro exposure to domoic acid and brevetoxin induces bottlenose dolphin immune cells to upregulate and express cytokines necessary to recruit eosinophils and eosinophil-derived Th2 cytokines modulate immune functions," using the specific aims: 1) measure and compare changes in bottlenose dolphin Th1 and Th2 cytokine profiles upon in vitro exposure to brevetoxin and domoic acid, 2) measure changes in lymphocyte proliferation and phagocytosis upon exposure to recombinant cytokine-activated eosinophils, and 3) measure changes in lymphocyte proliferation and phagocytosis upon in vitro exposure to eosinophil cationic protein (ECP). Immune cells were isolated from whole blood collected from healthy dolphins housed at Gulf World Marine Park and processed within 24 hours of collection. For objective one, we found no significant changes in Th1 or Th2 cytokines concentrations as a result of DA or brevetoxin exposure. We are currently in the processing of testing objective two. For objective 3, ECP did significantly decrease lymphocyte proliferation with the T cell mitogen ConA, but only at the highest ECP concentration tested, 2 x 10^-9 M. In contract, ECP significantly increased unstimulated (no mitogen) lymphocyte proliferation only at the two middle concentrations of ECP tested, 1 x 10^-11 and 1 x 10^-10 M. Only ECP at a concentration of 1 x 10^-8 M significantly reduced neutrophil phagocytosis. At this point in the project, it appears that ECP at the tested concentrations modulated important innate and adaptive immune functions in bottlenose dolphins.

Acknowledgments

Funding for this project is supported by the FY 2012 John H. Prescott Marine Mammal Rescue Assistance Grant Program (Prescott Grant Program), #NA12NMF4390161. We would also like to thank the Gulf World Marine Park (Panama City Beach, FL) for providing bottlenose dolphin blood samples.

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