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)