Regulation of in vitro myelopoiesis by a hemopoietic stromal fibroblastic cell line.

An adherent cell line (AP63) derived from murine spleen was characterized as fibroblastic, and several of its properties distinguished it from other adherent cells (i.e., macrophages and endothelial cells). The ability of the AP63 cells to regulate in vitro myelopoiesis was investigated. Medium conditioned by the cell line (CM) induced granulocyte-macrophage (GM) colonies, thus demonstrating the production of colony-stimulating activity by AP63 cells. A relatively large proportion of these colonies had a "tight" morphology and contained many early myeloid cells and cells capable of secondary cluster and colony formation. CM also contained a prostaglandinlike inhibitor of colony formation. Furthermore, AP63 cells inhibited GM colony formation by bone marrow cells in their immediate vicinity, whereas colony formation was stimulated at greater distances. These observations may reflect in vivo regulatory properties of hemopoietic stromal fibroblasts with respect to proliferation and differentiation of GM progenitor cells.