Goldschneider Irving
Department of Immunology, University of Connecticut Health Center, Farmington, CT 06030, USA.
Immunol Rev. 2006 Feb;209:58-75. doi: 10.1111/j.0105-2896.2006.00354.x.
It has recently been observed, as in the fetal thymus, that the importation of hematogenous thymocyte progenitors by the adult thymus is a gated phenomenon, whereby saturating numbers of progenitors periodically enter the thymus and occupy a finite number of intrathymic niches. In addition, the mobilization of thymocyte progenitors from the bone marrow appears to be a cyclical process that coincides temporally with the periods of thymic receptivity (open gate). It is proposed that these events are coordinated by a thymus-bone marrow feedback loop in which a wave of developing triple negative (CD3- CD4- CD8-) thymocytes interacts with stromal cells in the stratified regions of the thymus cortex to sequentially induce the release of diffusible cytokines that regulate the production, mobilization, and recruitment of thymocyte progenitors. The likely components of this feedback loop are described here, as are the properties of the intrathymic vascular gates and niches for thymocyte progenitors. The cyclical production and release of thymocyte progenitors from the bone marrow is placed in the context of a general phenomenon of oscillatory feedback regulation involving all lymphohemopoietic cell lineages. Lastly, the question of whether the gated (as opposed to the continuous) entry of thymocyte progenitors is essential for normal thymocytopoiesis in adult life is discussed.
最近观察到，如同在胎儿胸腺中一样，成年胸腺对血源性胸腺细胞祖细胞的输入是一种有门控的现象，即大量祖细胞周期性地进入胸腺并占据有限数量的胸腺内龛位。此外，胸腺细胞祖细胞从骨髓的动员似乎是一个周期性过程，在时间上与胸腺接受期（开放门控）相吻合。有人提出，这些事件是由胸腺 - 骨髓反馈回路协调的，在这个回路中，一波发育中的三阴性（CD3 - CD4 - CD8 -）胸腺细胞与胸腺皮质分层区域的基质细胞相互作用，依次诱导可扩散细胞因子的释放，这些细胞因子调节胸腺细胞祖细胞的产生、动员和募集。这里描述了这个反馈回路可能的组成部分，以及胸腺细胞祖细胞的胸腺内血管门控和龛位的特性。骨髓中胸腺细胞祖细胞的周期性产生和释放被置于涉及所有淋巴细胞生成细胞谱系的振荡反馈调节这一普遍现象的背景下。最后，讨论了胸腺细胞祖细胞的门控（而非连续）进入对于成年期正常胸腺细胞生成是否至关重要的问题。
