Characteristics of neutrophil chemotaxis in bottlenose dolphin (Tursiops truncatus)

Cetaceans have adapted to aquatic life by evolving various anatomic and physiologic traits, but biological defense mechanisms specific to aquatic mammals that protect against pathogenic microorganisms in the aquatic environment have not been elucidated. In this study, we investigated the migration of polymorphonuclear leukocytes in bottlenose dolphins in response to various chemotactic factors and compared the migration response with that of terrestrial animals such as cows and humans to characterize biological defense mechanisms unique to cetaceans. Bottlenose dolphin neutrophils showed strong chemotactic activity toward zymosan-activated serum and recombinant human interleukin-8 but no chemotaxis toward N-formyl-methionyl-leucyl-phenylalanine or leukotriene B₄ at any concentration examined. Bovine and human neutrophils showed the strongest chemotactic activity at 37°C, whereas chemotactic activity declined significantly at 15°C and 4°C. By contrast, bottlenose dolphin neutrophils exhibited relatively strong chemotactic activity even at 15°C. These results suggest that the mechanism by which bottlenose dolphin neutrophils detect chemoattractants differs from that of terrestrial mammals and that the immune system of cetaceans may be cold-adaptive, allowing the animals to exert robust host defense responses in aquatic habitats, which tend to be colder than the terrestrial environment.