Meeting Abstract

P3.95  Wednesday, Jan. 6  Does nutritional state affect immune function in frogs? BLACK, Samuel J*; CRESPI, Erica J; Vassar College; Vassar College sablack@vassar.edu

With emerging diseases threatening global amphibian populations, there is a need to understand the physiological mechanisms that influence susceptibility to infection in frogs and salamanders. Because variation in nutritional status is one of the main factors known to affect the immune system in other vertebrates, we investigated the effects of food restriction on immune function in juvenile Xenopus laevis. First, we compared red blood cell (RBC) and white blood cell (WBC) densities in hematological smears obtained from fed and 1-month food-deprived juveniles of three size classes. We also challenged both fed and food-deprived animals with the mitogen phytohaemagglutinin (PHA, 50 ug/g dose), which is known to stimulate proliferation in targeted cell types. Even though we did not detect a main effect of nutritional state on total RBC counts, we found that only fed animals experienced the stimulatory effect of the PHA, while food restricted animals experienced a decrease in RBCs after PHA injection. We also did not find overall effects of nutrition or PHA on total WBC counts. However, the ratio of heterophils to lymphocytes (H:L), which is particularly sensitive to stress, was increased in food-deprived animals. These findings suggest that nutritive condition may not affect baseline levels of RBC or WBC, but food restriction may impair the animal’s ability to up-regulate RBC proliferation, potentially in situations when an increase in oxygen consumption may benefit the health of the animal. This impairment could be due to an overall reduction in metabolic activity in the food-deprived animals, or due to a down-regulation of mitogenic factors related to reduced energetic reserves. In addition, the increased H:L ratio in food-restricted frogs reflects some interaction between nutritional status and immune function.