, Volume 167, Issue 4, pp 256-263

Changes in selected aspects of immune function in the leopard frog, Rana pipiens, associated with exposure to cold

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The effect of exposure to low temperatures (5 °C) on lymphocyte proliferation, leukocyte populations, and serum complement levels was examined in the northern leopard frog, Rana pipiens. Proliferation of T lymphocytes in response to phytohemagglutinin stimulation was significantly decreased in frogs kept for 2, 3, and 5 months at 5 °C compared to that of animals kept at 22 °C. A significant increase in the average percentage of neutrophils and a decrease in the mean percentage of eosinophils was observed in the blood of frogs held for 5 months in the cold compared to animals held at 22 °C for the same length of time. Mean serum complement activity after 1 month at 5 °C was significantly reduced in comparison to animals held at 22 °C and was not detectable after 5 months in the cold. Recovery of complement levels at room temperature (22 °C) was also examined after cold exposure. Complement levels were significantly higher than controls (at 22 °C) in frogs returned to 22 °C for 7 and 14 days after 5 months in the cold. After frogs were held at 5 °C for 1 month, serum complement levels increased significantly within 2 days after returning to 22 °C and continued to rise 5 and 9 days after warming. Injections with Aeromonas hydrophila following a 5-week exposure to 5 °C failed to cause death or observable symptoms of disease in frogs that were returned to 22 °C.

Accepted: 20 November 1996