Meeting Abstract

P1.155  Saturday, Jan. 4 15:30  Synergistic effects of thyroid hormone and glucocorticoids on thymus gland involution in Xenopus laevis tadpoles MAUCH, E*; SCHREIBER, A.M.; St. Lawrence University, NY; St. Lawrence University, NY aschreiber@stlawu.edu

Metamorphosis in anurans is accompanied by a dramatic loss of larval thymocytes as a new adult antibody repertoire is formed. Rising levels of glucocorticoids (GC) during metamorphosis have been shown to inhibit lymphocyte proliferation and induce thymus lymphocyte cell death. Although increased thyroid hormone (TH) concentrations are known to mediate most aspects of metamorphosis, the influence of TH on the larval thymus, either directly or in combination with GC, remains unclear. Nieuwkoop-Faber stage 50 and 54 tadpoles were treated with TH (5nM T3) and dexamethasone (DEX, 2uM) individually and in combination for 4 days, after which thymus sizes were measured in vivo using image analysis. Treatment with either TH or DEX alone resulted in approximately 40% reductions of thymus size. In comparison, treatment with TH+DEX produced a 60% decrease in size. The kinetics of programmed cell death was evaluated in NF50 stage tadpoles using whole-mount immunohistochemistry against active caspase-3. Maximum thymus immunoreactivity following treatment occurred at 72 hours (TH), 48 hours (DEX), and 24 hours (TH+DEX). These findings suggest that TH and GC each separately induce larval thymus involution and apoptosis, and together exhibit a synergistic effect that accelerates these processes.