Abstract

The immune system, which protects the body from potential infectious agents, is critical for health maintenance and survival. Stress has been shown to have effects on the immune system, and may ultimately increase susceptibility to disease. Therefore, as part of the Chase Encirclement Stress Studies (CHESS), the effects of repeated chase and encirclement on the immune system of dolphins (Stenella attenuata) in the Eastern Tropical Pacific (ETP) were investigated. Lymphocytes were isolated from dolphin peripheral blood and labeled with monoclonal antibodies to cell surface proteins to measure specific lymphocyte subsets. In addition, lymphocytes were cultured and incubated with T and B cell dependent mitogens to measure proliferation.

Lymphocyte percentages and absolute cell numbers were obtained for T cells, B cells, T helper cells, and class II+ cells in the first time capture and encircled dolphin group (n=51) and the repeat capture group (n=10). There was a significant increase in T cell percentages and a significant decrease in B cell percentages (p<0.05) in the repeat capture group vs. the first time capture group. Males in the first time capture group had significantly higher absolute class II+, T cells, and T helper cells (p<0.05) than females in the first time capture group. Mature dolphins had higher percentages of T and T helper cells with significantly lower percentages of B cells than immature dolphins (p<0.05). Absolute lymphocyte, class II and B cell counts were significantly higher in immature vs. mature animals (p<0.05). There were no significant differences in lymphocyte proliferation for the first capture group vs. the repeat capture group of dolphins, although a decrease in B cell function was observed in those animals repeat captured on day three vs. day one. Confounding variables present in this study make it difficult to draw definitive conclusions; however, it is possible that changes in the lymphocyte percentages observed or decreases in lymphocyte function observed after three days recapture, may increase susceptibility to disease. This is the first report of lymphocyte subsets for this species as well as the first study of the investigation of the effects of a stressor--repeated chase and encirclement on the cetacean immune system.

Acknowledgements

This work was supported by a grant from the National Marine Fisheries Service contract # 40-AB-NF-108447 and the Office of Naval Research #N00014-00-1-0041. The authors wish to thank the CHESS team for their dedicated efforts in obtaining blood samples from dolphins in the Eastern Tropical Pacific. The authors pay special tribute, gratitude and honor to Dr. David St. Aubin. We thank Roger Geertsema (US Navy Marine Mammal Program) and Karin Fourney (Southwest Fisheries Science Center). We thank Dr. Jeffrey Stott (UC Davis) for the CD2 and CD21 antibodies and Drs. Stephen Reilly and Robert Brownell (Southwest Fisheries Science Center).