Goff L K, Larsson L, Fisher A G
ICRF Human Tumour Immunology Unit, Courtauld Institute of Biochemistry, London, GB.
Eur J Immunol. 1990 Mar;20(3):665-71. doi: 10.1002/eji.1830200330.
We have studied the expression of isoforms of CD45 (leukocyte common antigen, LCA) among T cell precursors using the organ culture system of Jenkinson et al. (Eur. J. Immunol. 1982. 12: 583). These experiments show that cells capable of recolonizing alymphoid embryonic thymic lobes in vitro can be detected in the thymus of fetal and adult mice and are enriched when thymocytes are depleted of cells bearing CD4 or CD8. These data are consistent with results from in vivo experiments of Fowlkes et al. (J. Exp. Med. 1985. 162: 802) indicating that T cell precursors lie within the double-negative (CD4-CD8-) compartment. No precursors were detected among the reciprocal populations of cells bearing CD4 and/or CD8 (single and double positives). Double-negative cell fractions were then divided on the basis of reactivity with monoclonal antibodies RA3-2C2 and RA3-3A1. These antibodies recognize the high molecular weight species of the LCA or, more accurately, a product defined by exon A of the CD45 gene. Recolonizing cells were found predominantly in the CD45RA+ (RA3-2C2 and RA3-3A1 reactive) fraction of double-negative thymocytes; CD45RA- enriched populations had increased efficiency of recolonization and CD45RA- depleted populations had decreased ability to recolonize as compared with the whole CD4-CD8- fraction. To clarify whether progenitors enriched in the CD45RA+ fraction were capable of giving rise to mature CD4+, CD8+ and CD4+ CD8+ cells, we analyzed the progeny of lobes seeded with CD4-CD8-CD45RA+ fractions. After 7-9 days in organ culture the proportion of CD4+, CD8+ or CD4+ CD8+ cells had increased to 35.2%, 18.6% and 23.7%, respectively (mean of five experiments), indicating that progenitors among the CD45RA+ population were indeed multipotent. These results suggest that the majority of T stem cells in the thymus are among thymocytes that express the CD45RA molecule, an hypothesis supported by our finding that removal of CD45RA-expressing cells (using complement and antibody) eliminated recolonizing capacity of thymic cell fractions.
我们使用詹金森等人（《欧洲免疫学杂志》，1982年，12卷：583页）的器官培养系统，研究了T细胞前体中CD45（白细胞共同抗原，LCA）同工型的表达。这些实验表明，在胎儿和成年小鼠的胸腺中可以检测到能够在体外重新定殖无淋巴细胞的胚胎胸腺叶的细胞，并且当胸腺细胞中携带CD4或CD8的细胞被清除时，这些细胞会富集。这些数据与福尔克斯等人（《实验医学杂志》，1985年，162卷：802页）的体内实验结果一致，表明T细胞前体位于双阴性（CD4-CD8-）区室中。在携带CD4和/或CD8的细胞（单阳性和双阳性）的相应群体中未检测到前体。然后根据与单克隆抗体RA3-2C2和RA3-3A1的反应性对双阴性细胞部分进行划分。这些抗体识别LCA的高分子量物种，或者更准确地说，识别由CD45基因的外显子A定义的产物。重新定殖细胞主要存在于双阴性胸腺细胞的CD45RA+（RA3-2C2和RA3-3A1反应性）部分；与整个CD4-CD8-部分相比，富含CD45RA-的群体重新定殖效率增加，而耗尽CD45RA-的群体重新定殖能力降低。为了阐明富含CD45RA+部分的祖细胞是否能够产生成熟的CD4+、CD8+和CD4+CD8+细胞，我们分析了接种CD4-CD8-CD45RA+部分的叶的后代。在器官培养7-9天后，CD4+、CD8+或CD4+CD8+细胞的比例分别增加到35.2%、18.6%和23.7%（五个实验的平均值），表明CD45RA+群体中的祖细胞确实是多能的。这些结果表明，胸腺中的大多数T干细胞存在于表达CD45RA分子的胸腺细胞中，这一假设得到了我们的发现的支持，即去除表达CD45RA的细胞（使用补体和抗体）消除了胸腺细胞部分的重新定殖能力。
