Microenvironment for thymocyte differentiation, selection and clonal elimination

本研究通过为期三年的“胸腺细胞分化、选择和克隆消除的微环境”项目，获得以下结论：1.胸腺和淋巴结中的细胞死亡模式（其中胸腺细胞被克隆删除或分别与生发中心的B细胞发生亲和力成熟）被证明不是细胞凋亡。在胸腺和生发中心，胸腺细胞或B细胞因固缩而死亡。因此，迫切需要重新考虑什么是细胞凋亡，如果胸腺中的克隆缺失不是通过细胞凋亡完成的，那么克隆缺失的意义何在.长期以来，人们一直认为类固醇给药引起的胸腺细胞严重和大量死亡是细胞凋亡。仔细的形态学检查在体内胸腺清楚地表明，即使在类固醇治疗后，胸腺细胞死亡的固缩，并立即死亡后，他们被吞噬的皮质巨噬细胞。3.平面电子显微镜对流式细胞仪分选的胸腺细胞的基础上FLS（细胞大小）和表面标记物确定了五个形态不同的亚群可能在不同的分化阶段。这一分析将是非常有用的，为未来的原位检查胸腺细胞，以追求他们的分化途径在胸腺。将BALB/c胸腺上皮细胞系（IT-76 MHC）注射到同种异体小鼠胸腺（C3 H）中，成功地建立了免疫耐受。机制尚待阐明。在小鼠胸腺中发现两种不同的巨噬细胞亚群，它们的位置、表面表型、形态和功能不同。这一发现将导致对胸腺微环境进行更精确的研究。

We obtained following conclusions through the 3-years' project entitled "Microenvironment for thymocyte differentiation, selection and clonal elimination".1. The pattern of cell deaths in the thymus and in the lymph nodes, where thymocytes are clonally deleted or affinity maturation takes place with B cells in germinal centers, respectively, was demonstrated not to be apoptosis. In the thymus and at germinal centers, thymocytes or B cells die by pyknosis. It is thus urgently necessary to reconsider what the apoptosis is and what the significance of clonal deletion if it is not accomplished by apoptosis in the thymus.2. Severe and massive thymocyte death due to steroid administration has long been believed to be apoptosis. Careful morphological examination of in vivo thymus clearly revealed that even after steroid treatment, thymocytes died by pyknosis, and immediately after they died by pyknosis they were engulfed by cortical macrophages.3.Plain electron microscopy on FACS-sorted thymocytes based on FLS (cell size) and surface markers identified five morphologically distinct subpopulations possibly at different differentiation stages. This analysis would be extremely useful for future in situ examination of thymocytes for pursuing their differentiation pathway within the thymus.4. Immunological tolerance was successfully established by injecting BALB/c thymic epithelial cell line (IT-76MHC) into allogeneic mouse thymuses (C3H). Mechanisms remain to be elucidated.5. Two different macrophage subsets were recognized in mouse thymus in terms of their location, surface phenotypes, morphology and functions. This finding would consequently lead to more precise investigation of the thymic microenvironment.