Study on Early Process of B Cell Differentiation

实验血液学现在有一系列生长因子，其中包含近20种作用于各种血细胞谱系细胞的不同分子。尽管列出尽可能多的造血生长因子是重要的，然而，随着参与造血系统的分子数量的增加，对整个造血系统有一个清晰的图像变得更加困难。这个国际合作实验室项目的主要目的是为建立一个简化的造血系统模型铺平道路，在这个项目的过程中，两个生长因子/受体系统被证明构成了造血系统的核心结构。一个是c-fms/M-CSF系统，另一个是c-kit/SCF系统。D. Schultz在杰克逊实验室的研究中，我们已经证明了一种突变，骨硬化症（OP），是M-CSF编码区的一个单核苷酸插入，通过该插入，M-CSF的生物学活性被废除。进一步的组织学检查 ...更多信息 证实了在没有M-CF的情况下维持巨噬细胞生成。另一方面，破骨细胞的生成是制备骨腔所不可缺少的，它完全依赖于M-CSF。没有骨腔就没有骨髓造血，c-fms/M-CSF系统可能是维持骨髓造血的重要系统，但如果没有支持干细胞自我更新的系统，即使有骨腔也不能维持骨髓造血。以往对c-kit及其配体功能缺陷的突变小鼠的表型分析表明，该系统可能构成造血干细胞自我更新的核心结构。为了验证这种可能性，我们建立了分泌抗c-kit单克隆抗体的杂交瘤。利用其中一株能阻断c-kit功能的单克隆抗体，研究了c-kit/SCF系统在骨髓造血中的作用。我们的研究结果表明，髓系和红系干细胞的自我更新完全需要c-kit/SCF。与亚拉巴马大学的马克斯库珀博士合作，FritzMelchers和巴塞尔免疫学研究所的罗纳德帕拉西奥斯、弗里茨Melchers和AntoniusRolink等博士的研究中，我们还证实了c-kit在早期淋巴细胞前体细胞系的表面表达。综上所述，c-kit/SCF系统构成了包括淋巴样干细胞在内的各种造血干细胞自我更新的核心分子结构，由此我们提出了一个简化的模型，即受体型酪氨酸激酶及其配体构成了骨髓造血的核心结构，其他细胞因子受体家族分子及其配体被置于该核心结构周围，可能起着保证造血系统灵活性的作用。这个模型可以通过研究造血系统的发育和个体发育来检验，我们实验室目前正在进行这方面的研究。少

Experimental hematology has now a list of growth factors, which contains nearly 20 distinct molecules acting on the cells of various blood cell lineages. Although it is important to list as many hematopoietc growth factors as possible, however, it become more difficult to have a clear image of hematopoietic system in toto as the number of molecules involved in the system increases. The major purpose of this international collaboratory project is pave a way towards a simplified model of hematopoietic system.During the course of this project, two growth factor/receptor systems have been demonstrated to constitute the core structure of hematopoietic system. One is c-fms/M-CSF system, and the other is c-kit/SCF system.First, in collaboration with Dr. L. D. Schultz in Jackson Laboratory, we have demonstrated that a mutation, osteopetrosis(op), is a single nucleotide insertion within M-CSF coding region, by which biological activity of M-CSF is abrogated. Further histological examination ind … More icated that macrophage generation is maintained in the absence of M-CF. On the other hand, osteoclast generation whuch is indispensable for preparing bone cavity, is absolutely dependent on M-CSF. Noting a simple fact that there is no intramarrow hematopoiesis without bone cavity, c-fms/M-CSF system may well be a essential system for maintaining the intramarrow hematopoiesis.Even in the presence of bone cavity, however, no intramarrow hematopoiesis is maintained if the system supporting self-renewal of stem cell is absent. Since Previous phenotype analysis of mutant mice defective in the functions of c-kit or its ligand suggested that this system could constitute the core tructue for hematopoietic stem cell self-renewal. To test this possibility, we have estabished hybridomas which secrete anti-c-kit moneclonal antibody. Using one of these mAb which can block c-kit function, we investigated the role of c-kit/SCF system in intramarrow hematopoiesis. Our result indicated that the self-renewal of myeloid and erythroid stem cells requires c-kit/SCF absolutely. In collaboration with Dr. Max Cooper in Alabama Univ., Frirtz Melchers, and Drs. Ronald Palacios, Fritz Melchers, and Antonius Rolink in Basel Institute for Immunology, we also demonstrated that c-kit isexpressed on the surface of early lymphocyte Precursors cell lines. Taken together, it is clear that c-kit/SCF system constitutes a core molecular structure for the self-renewal of all kinds of hematopoietic stem cells including lymphoid stem cells.From these results, we are proposing a simplified model that receptor type tyrosine kinases and their ligands form a core structure of intramarrow hematopoiesis, and other cytokine receptor family molecules and their ligands are placed around this core structure, Probably Playing a role for ensuring the flexibility of hematopoietic system. This model might well be testable by investigating phylogenical and ontogenical development of hematopoietic system, and the investigation along this line is currently carried out in our laboratory. Less