Early B cell precursors in long-term bone marrow culture: selective development in the bone marrow of irradiated recipients

Differentiation of canine bone marrow cells with hemopoietic characteristics from an adherent stromal cell precursor

Stromal cell lines were established from canine long-term marrow cultures, cloned by limiting dilution, and maintained in stromal cell-conditioned medium. These cells grew adherent, maintained stable growth rate and morphology under standard conditions (in 20-30% conditioned medium; confluency, 70-90%), and supported hemopoiesis in long-term marrow cultures. In the presence of exogenous recombinant canine stem cell factor (rcSCF), round cells developed from the adherent layer, detached, and remained in culture as viable floating cells. Round floating cells also appeared when cultures were grown to > 90% confluency without rcSCF. Round cells were smaller than adherent cells, expressed CD34, showed basophilic plasma, and stained positive for c-kit, MHC-class II markers, and myeloid markers. In standard assays for colony formation, the detached cells produced granulocyte-macrophage colony-forming units (CFU-GM), fibroblast colony-forming units (CFU-F), and less well-defined colony-forming units. In addition, on allogeneic feeder cells in long-term cultures, these cells generated hemopoietic colonies. Strikingly, the differentiation was reversible: when nonadherent cells were resuspended at lower density in serum-containing medium, they reattached and grew to confluence when, once again, round cells detached. Detached cells from this secondary cycle produced mainly CFU-F and few CFU-GM when placed in clonal assays. These results suggest that some fibroblast-like stromal cells have the potential to differentiate into cells with hemopoietic characteristics. These observations provide evidence for the existence of a quiescent precursor of hemopoietic progenitors in the bone marrow stroma of the adult dog.

Establishment of IL-5-dependent early B cell lines by long-term bone marrow cultures

We established two different IL-5-dependent Ly1+ early B cell lines in long-term bone marrow culture system. One of them (J-87) is stromal cell (ST2) dependent and the other (T-88) is ST2 independent. Both J-87 and T-88 are B220+, Ly1+, sIgM-, Ia-, Thy1-, and IL-2R+, and respond to IL-3 and IL-5 in the presence of ST2. The T-88 can proliferate only in response to IL-5 in the absence of ST2. Southern blot analysis using JH probe revealed that configuration of IgH gene of both cell lines shows rearranged pattern. Binding assay for radiolabeled IL-5 to T-88 demonstrated that T-88 has two classes of IL-5 binding sites (low and high affinity) on the membrane. These data strongly suggest that there are IL-5-sensitive stages at both stromal cell-dependent and stromal cell-independent phases in early B cell development.

Monoclonal anti-Thy-1.2 antibody induced hematopoiesis in vivo

The intravenous injection of a monoclonal anti-Thy-1.2 alloantibody (IgM class) induced a rapid increase in the number, and the ratio, of multipotent hematopoietic stem cells (CFU-S) in S-phase. The onset of hematopoiesis was thymus-independent. Reconstitution of lethally-irradiated mice with bone marrow cells from mice injected with antibody augmented the T-cell responsiveness to mitogens. No activation was observed in granulocyte/macrophage progenitors. The monoclonal antibody did not directly stimulate CFU-S in vitro, although hematopoietic activity could be found in the sera of antibody-injected mice. Immediately after injection, the antibody was found bound on Thy-1+ cells in spleen. No decrease in the number of peripheral T cells was seen. These results seem to indicate that Thy-1.2-positive cells bound with anti-Thy-1.2 alloantibody may secrete a factor which induces the proliferation of hematopoietic stem cells.

Immunoglobulin heavy chain gene diversification in the long-term bone marrow culture of normal mice and mice with severe combined immunodeficiency

The change of immunoglobulin heavy (H) chain gene configuration during the differentiation of B cells from their early precursors was investigated in long-term cultures of bone marrow cells (LTBC). Hemopoietic stem cells are maintained in LTBC described by Dexter et al. (J. Cell. Physiol. 1977. 91: 335; LTBC-D), which supports the differentiation of myeloid lineage cells but not B lineage cells. By simply shifting the culture condition to that devised by Whitlock and Witte (Proc. Natl. Acad. Sci. USA 1982. 79: 3608; LTBC-B) to support the development of B lineage cells, surface IgM-bearing (sIgM+) B cells became detectable by the 2nd week after the shift and the number quickly increased thereafter, while the number of polymorphonuclear cells and granulocyte-macrophage colony-forming cell (CFU-c) decreased rapidly. H chain gene configuration of the developing cells in the culture was examined by Southern blot analysis of Eco RI-digested DNA with a JH probe. Whereas rearranged JH gene configuration was not detectable in the DNA from LTBC-D cells, it first appeared 2 weeks after the shift, and the level of the rearrangement rapidly increased thereafter as the intensity of JH band of germ-line configuration decreased. Almost all the cells in the culture had undergone H chain gene rearrangement in both chromosomes by the 6th week after the shift. During 2 to 4 weeks after the shift, a cluster of bands spanning around 4.5-5.5 kb appeared dominant among the rearranged configurations of JH gene and then it decreased in intensity as the pattern of JH band became a more homogeneous smear. The distribution of rearranged JH bands observed during 3-4 weeks after the shift was strikingly similar to that observed in normal spleen B cells. By semi-quantitative analysis of the intensity of JH and DSP2 bands remaining in germ-line configuration, it was found that the loss of germ-line JH band was far more rapid than that of germ-line DSP2 bands in the developing B cells in vitro. This result is consistent with the conclusion obtained in B cell tumor lines that D to J assembly occurred first and was followed by V to DJ assembly in this culture system. Taken together, it is likely that the process of H chain gene diversification in this culture system may represent the actual process during B cell differentiation in vivo. Differentiative capacity of bone marrow stem cells from mouse with severe combined immunodeficiency (SCID) was also analyzed in the same culture system.(ABSTRACT TRUNCATED AT 400 WORDS)