Nakanishi M
Department of Pediatrics, Hokkaido University School of Medicine, Sapporo, Japan.
Hokkaido Igaku Zasshi. 1994 May;69(3):515-26.
Premature thymocytes proliferate and differentiate from immature to mature T lymphocytes through out both positive and negative selections in thymus. The clonal deletion is a major mechanism of cell selection and mainly depends on apoptosis. Recently, Itoh et al. isolated cDNAs encoding Fas antigen which mediate apoptosis and is expressed on mouse thymocytes. Herein, I further attempted to examine the expression of Fas antigen gene in human thymocytes from thymus resected at cardiac operations. Human thymocytes were separated into 5 fractions with discontinuous gradient using bovine serum albumin (BSA). They consisted of fractions I (BSA concentrations: 10-14%), II (14-16%), III (16-18%), IV (18-20%), and V (20-24%). Human thymocytes in each fraction were characterized regarding the rearrangement of T cell receptor (TCR) genes and the expression of human Fas antigen gene. Human thymocytes were divided into three sub populations according to their stages of differentiation and maturation. First population, thymocytes contained in fraction I, expressed interleukin 2 receptor alpha-chain (IL-2R alpha) and proliferated without the presence of recombinant IL-2 (rIL-2). Second, thymocytes contained in fraction II and III, expressed IL-2R alpha but could not proliferate without the presence of rIL-2. Third, thymocytes contained in fraction IV and V, could not express IL-2R alpha nor proliferate under any conditions assayed, and occupied over 90% of total human thymocytes in number. The southern blot analysis of T cell receptor beta-chain gene constant region (C beta) showed that C beta were rearranged in most of all thymocytes except for small population contained in fraction I. The reverse transcription-polymerase chain reaction (RT-PCR) analysis of Fas antigen gene expression revealed that the thymocytes in fraction I expressed Fas antigen gene more than those in any other fractions and that the thymocytes in fraction V expressed no Fas antigen gene. These results suggested that Fas antigen plays a minor role in the clonal deletion of postnatal human thymocytes.
早产胸腺细胞在胸腺中通过阳性和阴性选择从幼稚状态增殖并分化为成熟的T淋巴细胞。克隆性缺失是细胞选择的主要机制，主要依赖于细胞凋亡。最近，伊藤等人分离出了编码Fas抗原的cDNA，该抗原介导细胞凋亡并在小鼠胸腺细胞上表达。在此，我进一步尝试检测在心脏手术中切除的胸腺来源的人胸腺细胞中Fas抗原基因的表达。使用牛血清白蛋白（BSA）通过不连续梯度将人胸腺细胞分离为5个组分。它们分别为组分I（BSA浓度：10 - 14%）、II（14 - 16%）、III（16 - 18%）、IV（18 - 20%）和V（20 - 24%）。对每个组分中的人胸腺细胞进行T细胞受体（TCR）基因重排和人Fas抗原基因表达的特征分析。根据分化和成熟阶段，人胸腺细胞被分为三个亚群。第一群，包含在组分I中的胸腺细胞，表达白细胞介素2受体α链（IL - 2Rα），并且在没有重组IL - 2（rIL - 2）的情况下增殖。第二，包含在组分II和III中的胸腺细胞，表达IL - 2Rα，但在没有rIL - 2的情况下不能增殖。第三，包含在组分IV和V中的胸腺细胞，在任何检测条件下都不表达IL - 2Rα也不增殖，并且在数量上占总人胸腺细胞的90%以上。T细胞受体β链基因恒定区（Cβ）的Southern印迹分析表明，除了组分I中包含的少量细胞外，大多数胸腺细胞中的Cβ发生了重排。Fas抗原基因表达的逆转录 - 聚合酶链反应（RT - PCR）分析显示，组分I中的胸腺细胞比其他任何组分中的胸腺细胞表达Fas抗原基因更多，并且组分V中的胸腺细胞不表达Fas抗原基因。这些结果表明Fas抗原在出生后人胸腺细胞的克隆性缺失中起次要作用。
