abstract

Evolutionary and environmental adaptations of the dolphin immune system are not well understood. The incidence of pathogens such as morbillivirus, papillomavirus, gammaherpesvirus and Brucella warrant investigation of the dolphin immune system and more specifically, investigations of the mechanisms that have evolved to combat viruses and tumors versus bacteria. Of particular interest are natural killer cells which are a type of lymphocyte that can target and kill both virally infected and tumor cells without prior exposure. Natural killer cells are distinguished from other lymphocytes by the presence of the cell surface protein CD56. The gene for CD56 has currently been sequenced in five different terrestrial mammalian species but no information is available for marine mammals. As a first step in studying this protein in marine mammals and its significance, CD56 was obtained and cloned by standard molecular techniques including extracting RNA from dolphin white blood cells, cerebellum, and adrenal tissue followed by cDNA synthesis and amplification by the polymerase chain reaction (PCR). Sequencing revealed the dolphin CD56 gene to be 2547 nucleotides in length, translated to a protein of 849 amino acids. The dolphin CD56 nucleotide sequence is 91% homologous to the human CD56 nucleotide sequence, with bovine sharing the highest percentage homology (94%) with dolphin. At the protein level, dolphin CD56 is 95% homologous with feline, bovine and human. Dolphin CD56 contains identical protein motifs as other CD56 terrestrial mammals, suggesting a similar protein structure. Further study of this molecule and the development of molecular tests and reagents to use in functional tests for dolphin natural killer cell function will be useful in further examination of the processes involved in dolphin viral and tumor immunity.

acknowledgements

This research was supported at Mystic Aquarium & Institute for Exploration through funding from the Office of Naval Research (N00014-06-0297) and at Union College through Union College's Internal Education Foundation and the Department of Biological Science.