Abstract

An essential prerequisite for developing successful vaccination programs is the ability to delineate the character and magnitude of the vaccine-induced antigen-specific immune response, and ultimately to examine vaccine efficacy by direct pathogen challenge. In view of the economic and operational value of captive cetaceans, direct live-pathogen challenges are not realistic. Therefore, we must rely on information from other mammalian species and in vitro marine mammal assays to determine which delivery systems (antigens, adjuvants, route of immunization, etc.) elicit the appropriate protective immune response (cellular, humoral, TH1, TH2 and/or TH3). While this information is essential for developing effective vaccines, it is also important in minimizing the risk of adverse effects in these valuable animals; there is ample literature describing the induction of inappropriate immune responses following infection and/or immunization, resulting in exacerbated clinical disease upon exposure to the virulent organism.

Since the most effective vaccines induce an immune response closely resembling the protective response invoked by the natural infection itself, our approach is directed at defining the immune responses associated with natural infections of Erysipelothrix rhusiopathiae, and comparing them with the responses induced by vaccination with a commercially available, adjuvanted, vaccine. Blood samples were collected from dolphins prior to vaccination, at the time of a 2nd immunization (booster), and then 2 weeks following the booster. In addition samples were collected from a subset of animals 2-3 days following the 2nd immunization. Peripheral blood leukocytes were subjected to analytical flow cytometry to identify vaccine-associated perturbations in lymphocyte phenotype and/or cell-surface density of leukocyte activation and adhesion proteins. Mononuclear leukocytes were cryopreserved for analysis of antigen-specific cellular immune responses. mRNA was purified from peripheral blood leukocytes that were collected in PaxGene vacutainers tubes. These latter samples will be used to identify vaccine-associated perturbations in cytokine production. Assays were developed for qualitative and quantitative identification of Tursiops cytokines associated with humoral, cellular, proinflammatory and/or anti-inflammatory immune responses (IL-2, IL-4, IL-5, IL-6, IL-10, IL-13, IL-18, TNF, TGF and IFN). While all data is not yet complete, the broad concepts of this study are applicable to assessing vaccine efficacy to other pathogens.

Acknowledgments

We gratefully acknowledge the Veterinary Staffs at SeaWorld of Orlando, Texas and California for providing the blood samples. Supported in part by the Office of Naval Research, Grant #N00014-04-1-0159.