title: Characterization of early B lymphocyte precursors present in long-term bone marrow cultures.
abstract: Lymphoid precursor cells are present in long-term bone marrow cultures (LTBMC), but their differentiation into mature lymphocytes is blocked. A quantitative assay for B cell precursors in LTBMC, which gives a linear relationship between the number of grafted LTBMC cells and the frequency of B cell colony forming units (CFU-B) in the spleen and bone marrow of immunodeficient CBA/N mice 19 days after reconstitution, is described. Characterization of the B cell precursor indicates that this assay is detecting a very early precursor and not a B lymphocyte or a late pre-B cell. This conclusion is based on the observations that a) pre-B cells transformable by Abelson murine leukemia virus are not present in LTBMC by 3 days postrecharge and CFU-B are absent by 6 days postrecharge; b) late B cell progenitors capable of rapid repopulation of irradiated CBA/N mice are not present in LTBMC, since a lag in the kinetics of B cell reconstitution in animals grafted with LTBMC cells is observed compared with fresh bone marrow cells; c) the B cell precursors in LTBMC have high proliferative potential, since they can stably repopulate recipient mice for at least 8 wk postreconstitution and through two serial passages in irradiated CBA/N recipients; and d) the B cell precursors are large, rapidly sedimenting cells as determined by velocity sedimentation. The serial transplantation experiment further shows that a split is often observed between lymphoid and myeloid reconstituting ability of LTBMC cells. The LTBMC B cell precursor may be a pluripotent stem cell or a lymphoid stem cell, although its differentiative potential remains to be determined.
mesh_terms: D000011:Abelson murine leukemia virus / Q000276:immunology; D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology; D001799:Blood Sedimentation; D001853:Bone Marrow / Q000276:immunology; D001854:Bone Marrow Cells; D016026:Bone Marrow Transplantation; D002448:Cell Adhesion; D002469:Cell Separation; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D005260:Female; D006410:Hematopoiesis; D007700:Kinetics; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008808:Mice, Inbred CBA; D013234:Stem Cells / Q000166:cytology* / Q000276:immunology; D013997:Time Factors