Choi E Y, Park W S, Jung K C, Kim S H, Kim Y Y, Lee W J, Park S H
Department of Pathology, Seoul National University College of Medicine, Korea.
J Immunol. 1998 Jul 15;161(2):749-54.
CD99 is a cell surface molecule involved in the aggregation of lymphocytes and apoptosis of immature cortical thymocytes. Despite its high level expression on immature cortical thymocytes, the functional roles of this molecule during thymic selection are only now being elucidated. Examination of the effects of CD99 engagement on the expression kinetics of the TCR and MHC class I and II molecules, which are involved primarily in thymic positive selection, revealed a marked up-regulation of these proteins on the surface of immature thymocytes. This increase was the result of accelerated mobilization of molecules stored in cytosolic compartments to the plasma membrane, rather than increased RNA and protein synthesis. Confocal microscopic analysis revealed the changes in subcellular distribution of these molecules. When CD99 was engaged, TCR and MHC class I and II molecules were concentrated at the plasma membrane, particularly at cell-cell contact sites. The TCRlow subpopulation of immature double positive thymocytes was much more responsive to CD99-mediated up-regulation than was the TCRhigh population. These findings suggest that CD99-dependent up-regulation may have possible implication in positive selection during thymocyte ontogeny.
CD99是一种细胞表面分子，参与淋巴细胞聚集以及未成熟皮质胸腺细胞的凋亡。尽管它在未成熟皮质胸腺细胞上高表达，但该分子在胸腺选择过程中的功能作用直到现在才被阐明。研究CD99激活对主要参与胸腺阳性选择的TCR以及MHC I类和II类分子表达动力学的影响，结果显示这些蛋白在未成熟胸腺细胞表面显著上调。这种增加是由于储存于胞质区室的分子加速转运至质膜，而非RNA和蛋白质合成增加所致。共聚焦显微镜分析揭示了这些分子亚细胞分布的变化。当CD99被激活时，TCR以及MHC I类和II类分子集中于质膜，尤其是在细胞-细胞接触部位。未成熟双阳性胸腺细胞的TCRlow亚群比TCRhigh亚群对CD99介导的上调反应更强烈。这些发现表明，CD99依赖性上调可能在胸腺细胞发育过程中的阳性选择中具有潜在意义。
