The expression of c‐kit ligand and interleukin 6 (IL‐6) genes in mouse bone marrow‐derived stromal cell lines was examined using quantitative polymerase chain reaction (PCR) analysis based on the design of an internal DNA control. The stromal cells studied included the 14F1.1 endothelial‐adipocytes that support long‐term hemopoiesis and two additional cell lines (MBA‐1, MBA‐13) which do not have this function. All the cell lines expressed c‐kit ligand gene constitutively, and this expression was not increased by lectins. On the other hand, the expression of the IL‐6 gene was markedly induced in all the lines by lipopolysaccharide (LPS) and by phorbol 12‐myristate 13 acetate (PMA). The constitutive expression of c‐kit ligand in 14F1.1 cells was the lowest among the three cell lines studied and could be increased by stimulation with IL‐4. Thus, we observed some quantitative differences among the cell lines in their expression of cytokine genes. However, the unique capacity of 14F1.1 cells to support in vitro hemopoiesis cannot thus far be explained solely on the basis of the ability of these cells to secrete cytokines which are not produced by other stromal cell lines. c‐kit ligand may be necessary, but its presence alone is not sufficient for 14F1.1 cells to support prolonged hemopoiesis.
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