Functional characterization of two stromal cell lines that support B lymphopoiesis

Bone marrow stromal cells have well documented effects on the production of B lymphocytes, but whether or not stromal cell signals are involved in the pre-B to B cell transition is unclear. The potential of two stromal cell lines, S10 and S17, in this process was examined. Initial experiments, using a short term liquid culture, indicated that S10 and S17 stroma efficiently supported the generation of clonable B cells (B lymphocyte CFU) from their immediate precursors in fresh bone marrow. The contribution of macrophages and other accessory cells in those experiments was minimized through use of a colony assay system that permits the direct effects of stromal cell signals on single B cell progenitors to be evaluated. The results indicated that soluble mediators from the S10 and S17 lines could support colony formation from fresh or cultured surface Ig- bone marrow cells. Colonies supported by S17 stroma appeared on day 15 and contained cells that expressed the B220 Ag; surface IgM expression was never observed. S10 supported colonies appeared on day 7 and routinely included surface IgM+ cells. Individual colonies were capable of undergoing additional growth when picked and replated directly onto the different stroma. Those colonies replated onto S10 stroma generated surface IgM expressing cells in up to 60% of experiments, but colonies transferred onto the S17 cell line included B cells only 10% of the time. These data demonstrate that stromal cells alone can provide the signals necessary for generating a surface IgM+ B cell from precursors but that not all stromal cell lines are equally efficient at doing so.