Witherden D A, Kimpton W G, Abernethy N J, Cahill R N
Department of Veterinary Science, University of Melbourne, Parkville.
Eur J Immunol. 1994 Oct;24(10):2329-36. doi: 10.1002/eji.1830241011.
The thymus plays an essential role in the generation and selection of T cells and exports approximately 0.5-1% of thymocytes per day in young animals and considerably fewer in older animals. To date there have been no studies directly examining fetal thymic export in any species. Using the technique of intrathymic injection of fluorescein isothiocyanate, followed by an assay for green fluorescent cells in the periphery and for the expression of cell surface antigens on these cells, we have compared directly the export of T cells from the fetal and postnatal ovine thymus. While the thymus exports both alpha beta and gamma delta T cells, our results demonstrate that the proportion of thymic gamma delta T cells that are exported per day is much higher than that of thymic alpha beta T cells. Moreover, the export rate of gamma delta T cells increased from approximately 1 in every 60 gamma delta thymocytes per day emigrating from the fetal thymus to 1 in every 20 from the postnatal thymus. In addition, we identify a population of CD5+CD4-CD8-gamma delta-. T cells emigrating from the fetal thymus but greatly reduced among thymic emigrants after birth. These findings have several implications regarding the mechanisms and control of selection of both gamma delta and alpha beta T cells.
胸腺在T细胞的产生和选择过程中发挥着至关重要的作用，在幼龄动物中，胸腺每天输出约0.5%-1%的胸腺细胞，而在老龄动物中输出的数量则要少得多。迄今为止，尚无任何研究直接检测过任何物种的胎儿胸腺输出情况。我们采用胸腺内注射异硫氰酸荧光素的技术，随后对外周血中的绿色荧光细胞以及这些细胞表面抗原的表达进行检测，从而直接比较了胎儿和出生后绵羊胸腺的T细胞输出情况。虽然胸腺输出αβ和γδ两种T细胞，但我们的结果表明，每天输出的胸腺γδ T细胞比例远高于胸腺αβ T细胞。此外，γδ T细胞的输出率从胎儿胸腺每天每60个γδ胸腺细胞中约有1个迁出，增加到出生后胸腺每20个γδ胸腺细胞中约有1个迁出。此外，我们还鉴定出一群CD5⁺CD4⁻CD8⁻γδ⁻ T细胞，它们从胎儿胸腺迁出，但在出生后的胸腺迁出细胞中数量大幅减少。这些发现对于γδ和αβ T细胞选择的机制及调控具有若干重要意义。
