Colony-stimulating activity production by hemopoietic organ fibroblastoid cells in vitro

We have demonstrated that hemopoietic organ fibroblastoid cells can produce colony-stimulating activity (CSA) in vitro. Skin fibroblasts also produced CSA. The colonies which formed were restricted to the granulocyte/macrophage differentiation pathways. A linear relationship was obtained for granulocyte/macrophage colony formation in the presence of a variable number of bone marrow-derived fibroblastoid colonies. Fibroblastoid cells did not produce biologically detectable burst-promoting activity for erythroid progenitors. The importance of these observations with respect to in vitro hemopoietic regulatory phenomena are considered.