Dolphin Immunology Research
By Jeff Stott, PhD and Myra Blanchard
University of California, Davis

This project is designed to provide a state-of-the-art assessment of the immunologic health of the dolphins in Sarasota Bay.  Advanced techniques are being applied to peripheral blood samples to characterize and/or identify leukocyte (white blood cell) subpopulations, lymphocyte function and inflammatory mediators.  Such measures complement the conventional immunologic data provided by a complete blood cell count (CBC) and serum chemistry panel.  Our current goal is to identify associations between specific immunologic perturbations and relative levels of environmental contaminants in various tissues.  In an attempt to identify contaminant-associated immunologic dysfunction, two additional approaches are being employed.  Firstly, blood samples are being obtained immediately upon capture, and then again just prior to release, in an attempt to associate an increased immunologic stress response with relatively high tissue contaminant levels.  More recently (initiated in 2003), mRNA has begun to be isolated from peripheral blood leukocytes and cryopreserved for the purpose of utilizing differential gene display for identifying immunologic and/or physiologic perturbations as a function of tissue contaminant load.  A panel of bottlenose dolpohin-specific genetic probes is currently being developed for identifying abnormal expression of a variety of pro- and anti-inflammatory immunologic mediators, heat shock proteins, endocrine pathways and metabolic enzymes associated with breakdown of environmental contaminants.

Baseline values for peripheral blood leukocyte subpopulations have been established for this free-ranging population of dolphins.  This data has identified significant age- and sex-associated differences in all leukocyte subpopulations.  This information indicates we need to sample a greater number of animals such that each age and sex group is sufficiently represented.  This will ultimately allow meaningful statistical comparison of contaminant levels and immunologic status.  Young animals have relatively high numbers of T and B lymphocytes, with these subpopulations declining rather dramatically by 30 years of age.  There is also a shift from naïve T lymphocytes (never exposed to antigen) to memory T lymphocytes as animals age.  Lymphocyte function, as determined by non-specific stimulation with T and B cell mitogens, is largely consistent, regardless of age and sex, assuming the animal is in a healthy state.

As would be expected, outliers in immunologic phenotype and function have been identified.  The implication of these findings, relative to animal health and survival, will become evident as the study proceeds.  While the application of differential gene display technologies will revolutionize our ability to identify contaminant-associated perturbations in animal health, leukocyte phenotyping and lymphocyte function data are already suggesting associations between total PCB’s and immunologic health.  While only two years of data have been analyzed to date, there is evidence that those animals with high contaminant loads have relatively decreased numbers of memory T lymphocytes and T:B lymphocyte ratios.  From a functional perspective, lymphocytes appear to be marginally compromised in those animals with the highest levels of contaminants in the year 2000.  This was not evident the following year (2001).  Immunologic and contaminant data will need to be analyzed from subsequent years to determine if the cell dysfunction in 2000 was merely an aberration or a reflection of as-yet-unidentified seasonal influences.  The modest dysfunction identified in lymphocytes derived from those animals with the highest levels of contaminants in 2000 was supported by decreased function following the stress of capture.  Those animals with the highest tissue levels of contaminants had a tendency to be those that experienced the greatest loss of T lymphocyte function following capture (comparison of the sample obtained immediately upon capture to the sample obtained just prior to release). 

In summary, these immunologic studies are not only establishing important immunologic baseline values for free-ranging bottlenose dolphins in Sarasota Bay, but are providing a sensitive tool for assessing the biological effects of environmental perturbations on animal health.  Funding for this research has been provided by NOAA Fisheries, International Whaling Commission, Office of Naval Research, Dolphin Quest, and the Laboratory for Marine Mammal Immunology, School of Veterinary Medicine, University of California-Davis