109.4 Saturday, Jan. 7 Leptin enhances proliferation of amphibian lymphocytes CRESPI, Erica J.*; FITES, J. Scott; ROLLINS-SMITH, Louise A.; Washington State University; Vanderbilt University Medical Center; Vanderbilt University Medical Center firstname.lastname@example.org
Leptin is a cytokine hormone that is best known for regulating food intake and energy expenditure, but recent studies in mammals have shown that it also affects immune responses in mammals. In amphibians, leptin has been shown to have similar effects on food intake, but relatively little is known about leptin’s interactions with the immune system. We tested the hypothesis that leptin is a modulator of splenocyte activity in adult Xenopus laevis, as the spleen is the main site of lymphocyte production in amphibians and the leptin receptor is expressed in X. laevis whole-spleen extracts. First, we examined the effects of leptin on proliferation of adult X. laevis lymphocytes with or without additional mitogenic stimuli in 3H-thymidine incorporation assays. As has previously been shown for mammalian species, leptin had a dose-dependent enhancement of lymphocyte proliferation driven by the T cell mitogens phytohemagglutinin (PHA) and phorbol myristate acetate (PMA), but unlike mammals, it caused a modest increase in proliferation when cells were treated with leptin alone. Leptin also enhanced T cell proliferation stimulated by allogeneic cells in a mixed lymphocyte response assay. In a separate experiment with X. laevis juveniles, leptin treatment increased the inflammatory response around the site of a saline injection, and leptin further enhanced inflammation after PHA injection. These data provide both in vitro and in vivo evidence that leptin is a pro-inflammatory cytokine that directly stimulates lymphocyte proliferation or survival in amphibians. These findings suggest that leptin’s immunomodulatory function is evolutionarily conserved across vertebrates, and leptin may be a nutritional cue that enhances the function of the immune system and contributes to the well-being of amphibians.