Ontogeny of Immunity in Frogs/Metamorphic Changes

9421349南非爪蛙的罗林斯-史密斯变态导致免疫系统发生显著变化。它的特点是胸腺和脾显着退缩，随后在变性后阶段淋巴细胞显著扩张。在其他一些两栖和爬行动物物种中，胸腺的退化是季节性的，在一些脊椎动物物种中，随着年龄的增长，胸腺会退化。在这些胸腺退化的大多数例子中，原因没有很好地定义。皮质类固醇激素(CH)已经被涉及，但对天然激素和特定激素受体拮抗剂的生理浓度的仔细研究尚未完成。为了确定CH是否是导致非洲爪哇胸腺退化和变态时淋巴细胞数量下降的原因，将测试两种特定的CH受体拮抗剂。体外研究将确定这些化合物在该系统中的有效性，并确定有效浓度范围。体内研究旨在抑制CH与其受体的结合，从而抑制可能由类固醇诱导的细胞死亡。CH诱导细胞死亡的可能机制是细胞程序性死亡或细胞凋亡。为了研究这一问题，将在变态前、变态中和变态后的几个阶段测定对照蛙和用CH-拮抗剂处理的蛙的胸腺和脾细胞群中的自发凋亡率。如果CH诱导的细胞凋亡是细胞衰退的一种机制，则应该被CH拮抗剂所抑制。如果胸腺细胞和脾细胞数量的减少不是由于CH诱导的细胞凋亡，这可能是由于变态高潮期间前体迁移和扩增速度降低所致。为了研究这个问题，二倍体(2N)前体向植入的三倍体(3N)胸腺的迁移率和扩张率将在高潮时被研究，并与在变态前和变态后观察到的相比较。更确切地说，这些研究将更准确地确定胸腺在变态过程中细胞死亡和替换的动态。幼蛙变态后的存活可能取决于它们对遇到蝌蚪的病原体做出记忆反应的能力。因此，我们想知道蝌蚪淋巴细胞在后变质期持续了多大程度。蝌蚪T细胞不同于T细胞，因为它们不表达第二类主要组织相容性复合体(MHC)抗原。设计了几个实验，以了解蝌蚪T细胞是否在变态过程中持续存在，并保持其蝌蚪表型，或者变成成体样并表达II类MHC。%这些实验将提供有关免疫系统在发育过程中的调节以及皮质类固醇激素在细胞程序性死亡中的作用的信息*

9421349 Rollins-Smith Metamorphosis in the South African clawed frog, Xenopus laevis, results in significant changes in the immune system. It is characterized by a striking involution of the thymus and spleen followed by significant lymphocyte expansion in the postmetamorphic period. Thymus involution is observed seasonally in some other amphibian and reptilian species, and with aging in a number of vertebrate species. In most of these examples of thymus involution, the causes are not well defined. Corticosteroid hormones (CH) have been implicated, but careful studies with physiological concentrations of natural hormones and specific hormone- receptor antagonists have not been done. To determine whether CH are responsible for thymus involution and the decline in numbers of lymphocytes at metamorphosis in Xenopus, two specific CH receptor antagonists will be tested. In vitro studies will establish the effectiveness of these compounds in this system and determine effective concentration ranges. In vivo studies are designed to inhibit binding of CH to their receptors and thus inhibit possible steroid-induced cell death. The likely mechanism of CH-induced cell death is programmed cell death or apoptosis. To examine this question, the rates of spontaneous apoptosis in the thymus and spleen cell populations of control frogs and frogs treated with CH- antagonists will be determined at several stages before, during, and after metamorphosis. If CH-induced apoptosis is a mechanism of cell decline, it should be inhibited by the CH-antagonists. If the decline in thymocyte and splenocyte numbers in not due to CH-induced apoptosis, it may be due to a decreased rate of precursor immigration and expansion during metamorphic climax. To examine this question, the rate of immigration and expansion of diploid (2N) precursors into an implanted triploid (3N) thymus will be studied at climax and compared with that observed at premetamorphic and postmetamorphic stages. C ollectively, these studies will more precisely define the dynamics of cell death and replacement in the thymus at metamorphosis. Survival of young postmetamorphic frogs might depend on their ability to mount a memory response to a pathogen encountered as a tadpole. Therefore, we would like to know to what extent tadpole lymphocyted persist in the postmetamorphic period. Tadpole T cells differ phenotypically from T cells because they do not express class II major histocompatibility complex (MHC) antigens. Several experiments are designed to learn whether tadpole T cells persist through metamorphosis and retain their tadpole phenotype or become adult-like and express class II MHC. %%% These experiments will provide information about the regulation of the immune system during development as well as the role of corticosterid hormones in programmed cell death ***