Factors determining T lineage commitment in haematopoietic stem cell.

T淋巴细胞在胸腺中分化成熟。多能造血干细胞（hsc）是进入胸腺还是转入T细胞谱系的祖细胞进入胸腺一直存在争议。目前还不清楚造血干细胞是如何与T细胞谱系结合的，少数T细胞是如何被选择的，以及成熟T细胞受体（TCR）库是如何形成的。利用电镜和免疫组织化学研究，我们试图在CTS小鼠胸腺中分离hsc （NOD的姐妹株，成熟T细胞从胸腺向外周迁移的缺陷）。应用分子生物学技术，研究了不同品系小鼠胸腺细胞的发育和胸腺选择。这些研究揭示了新的发现。我们用了一万多张电镜照片，在胸腺实质中经常发现中性粒细胞和嗜酸性粒细胞处于由髓细胞向中化髓细胞的发育阶段。我们还分离出红细胞（网织红细胞，呃…更多的红细胞）和巨核细胞。这是首次报道胸腺中存在巨核细胞，提示多系造血干细胞进入胸腺。通过RT-PCR证实了胸腺细胞因子的产生支持造血。总的来说，这些结果表明多系造血干细胞迁移到胸腺。不同品系小鼠成熟胸腺细胞的TCR库有很大差异，而早期未成熟胸腺细胞的TCR库则无差异。这表明，TCR的预选库是由一些在小鼠品系中保守的遗传因素决定的。我们发现CD4SP和CD8SP中CDR3长度缩短。CD4SP的CDR3缩短程度明显高于CD8SP，且不同品系的小鼠CDR3缩短程度不同，提示CDR3缩短受MHC单倍型的影响。CDR3的缩短依赖于V段。我们假设在种系中编码的Vbeta片段的结构特征影响CDR3的长度。少

T lymphocytes differentiate and mature in the thymus. It has been still controversial whether multi-potent haematopoietic stem cells (HSCs) enter the thymus or progenitors committed to T cell lineage do. It remains also unknown how HSCs are committed to T cell lineage, how a small number of T cells are selected or how mature T cell receptor (TCR) repertoire is formed. Using electron micrographic and immunohistochemical studies, we attempted to isolate HSCs in the thymus of CTS mice (sister strain to NOD, defect in emigration of mature T cells from the thymus to periphery). By using molecular biological technique, we studied thymocyte development and thymic selection in different strains of mice. Novel findings were revealed through these studies.1. We took more than ten thousand electron micrographs and frequently found neutrophils and eosinophils at the stage of development from the myelocyte to the metamyelocyte in the thymic parenchyma. We also isolated erythroids (reticulocytes, er … More ythrocytes) and megakaryocytes. This is the first report to demonstrate that presence of megakaryocytes in thymus, suggesting multi-lineage HSCs enter into the thymus. Cytokine production supporting hematopoiesis in the thymus was confirmed with RT-PCR. Collectively, these results suggest that multi-lineage HSCs immigrate into the thymus.2. TCR repertoire is largely different among different strains of mice in mature thymocytes but not in immature thymocytes at earlier stages. This suggests that pre-selection TCR repertoire is determined by some genetic factors conserved among mouse strains.3. We demonstrated that CDR3 length shortening was occurred in both CD4SP and CD8SP. The extent of CDR3 shortening was remarkable in CD4SP than in CD8SP and varied among different strains of mice, suggesting that the CDR3 shortening was influenced by MHC haplotype. The CDR3 shortening was dependent on V segment. We assumed that structural feature of Vbeta segment encoded in germline impacts on CDR3 length. Less