Ontogeny of Immunity in Frogs/Effects of Metamorphosis

南非爪蟾（Xenopus laevis）蝌蚪的免疫反应模式与成年爪蟾不同。变态是将两种模式分开的过渡时期。本研究的目的是检验一个假设，即成人免疫系统的发育需要变态，其特征是失去大量的幼虫淋巴细胞，代之以新的成人型淋巴细胞。为了证明或反驳这一假设，将对幼虫胸腺或脾脏细胞群进行细胞遗传学标记，并跟踪它们在变态期间和之后的命运。通过将三倍体胸腺或脾脏植入二倍体寄主体内，阻断其中部分寄主的变态，将确定变态T细胞群和B细胞群的更新是否依赖于甲状腺激素。因为变态是由甲状腺激素调节的，而甲状腺激素的作用可能受到皮质类固醇激素的调节，甲状腺激素和皮质类固醇激素在促进免疫系统变态依赖性变化中的直接作用将被分析。这些研究将有助于更好地理解两栖动物免疫系统的个体发生、个体发生过程中淋巴细胞产生的调节机制、免疫系统发育的神经内分泌调节以及对“自我”的免疫耐受如何发展。

The immune response pattern of tadpoles of the South African clawed frog, Xenopus laevis, is distinct from that of the adult. Metamorphosis is a transitional period that separates the two patterns. The objectives of this research are to examine the hypothesis that development of the adult immune system requires metamorphosis and is characterized by the loss of a major population of larval lymphocytes and replacement with new, adult- type lymphocytes. To prove or disprove the hypothesis, larval thymus or spleen cell populations will be cytogenetically labelled, and their fate during and after metamorphosis will be followed. By implanting triploid thymus or spleen into diploid hosts and blocking metamorphosis in some of them, it will be determined whether renewal of T and B cell populations at metamorphosis is dependent on thyroid hormones. Because metamorphosis is regulated by thyroid hormones whose effects may be modulated by corticosteroid hormones, the direct effects of thyroid hormones and corticosteroid hormones in promoting metamorphosis-dependent changes in the immune system will be analyzed. These studies will contribute to a better understanding of the ontogeny of the immune system of amphibians, the mechanisms that regulate production of lymphocytes during ontogeny, the neuroendocrine regulation of development of the immune system, and how immunological tolerance to "self" develops.