Fig. 6. Bone marrow precursor proliferation is highly enhanced by FSS supernatant. Total bone marrow cells (10⁶) were cultured for 7 days with supernatant from either fetal spleen stromal cell lines (FSS) or a bone marrow stromal cell line (S17), or with recombinant growth factors, alone or mixed, as indicated. (A) Cell differentiation was analyzed by FACS for macrophages (CD11c^- Mac1⁺ F4/80⁺ or F4/80^-) and DCs (CD11c⁺); the percentage of each population is indicated. (B) Proliferation of total bone marrow precursors was evaluated for each condition by counting the absolute number of live cells (Trypan blue exclusion). To evaluate whether FSS supernatant selectively acts on the proliferation and differentiation of particular precursors, the number of each cell type obtained was determined. The percentage of macrophages and DCs in the various conditions of culture (obtained by FACS analysis in A) was multiplied by the absolute number of live cells.