造血再生初期に出現する細胞群の形態学的追究 : 特に血液幹細胞について

A single high dose of 5-fluorouracil (5-FU) was administered intravenously in mice to induce the aplastic bone marrow and to seize the morphological characteristics of blood stem cells. Time course observations of histological and cytological changes in bone marrow hematopoiesis and stem cell assay revealed that the day 2 bone marrow contained a number of quiescent blood stem cells. For advanced morphological studies of blood stem cells, the day 2 marrow cells were seeded in methylcellulose culture medium for stem cell assay. Blast cell colonies (BCC) which contained CFU-GEMM (colony-forming unit granulocyte, erythroid, monocyte/macrophage, megakaryocyte) were formed within 2 weeks. BCC-constituting cells (BCC-cell) were lifted and processed for morphological analyses. The BCC-cells were variable in size as well as morphology, and were divided into 3 sub-groups according to their size. Large-sized group (> 14 μm) consisted of large blastic cells with a tendency of differentiation into early granulocyte or monocyte/macrophage lineage. Medium-sized group (10~ 14μm) consisted of more immature blastic cells which lacked a differentiation. Small-sized group (7~10μm) consisted of two celltypes. One type (named'transitional cell'or'TC cell') had distinctive features as a dark nucleus and a narrow basophilic cytoplasm seemed to be the most immature cell type. The other (named 'lymphoid cell') was morphologically indistinguishable from the small lymphocyte. Blast cell colony-replating experiments disclosed that the proportion of small-sized cells in BCC-cells (about 4%) was equivalent to the incidence of GEMM colonies formed in replated culture (about 2~5%). Furthermore, immunohistochemical staining of wheat germ agglutinin (WGA), anti-Thy- 1 antibody and anti-B cell antibody revealed that most of TC cells were positive for WGA suggesting of CFU-GEMM, and negative for anti-B cell antibody. Most of lymphoid cells were positive for anti-B cell antibody, and negative for WGA and anti-Thy-1 antibody, and were estimated to be true B-lymphocytes. Based on these results, it was reasonable to consider that a majority of TC cells were multipotent blood stem cells.