Colony‐stimulating factor and leukemia cell‐growth factor produced by a murine endothelial cell line, MKM‐O

A murine cultured cell line (MKM‐O) was established from a tumor of a BALB/C (nu/nu) mouse that had been subcutaneously inoculated with human hepatoma tissue fragments in the same location. The MKM‐O cell line was proven to be of endothelial origin by morphological examinations and positive staining with fluorescein‐labeled antibody against factor VIII antigen. MKM‐O cells grown in vitro produced a colony‐stimulating factor (CSF) and a leukemia cell‐growth factor (LC‐GF). CSF from MKM‐O acted on both human and murine bone marrow‐derived granulocytes and macrophage colony‐forming units (CFU‐GM). The activity of LC‐GF on human leukemia cell lines (HL‐60, HSB‐2, CEM, DAUDI and K562) was demonstrated both in conditioned medium (CM) of MKM‐O and of rat vascular endothelial cells. The CM of MKM‐O also demonstrated a limited growth promoting activity against the mononuclear cells from human cord blood and improved their survival, suggesting that endothelial cells play an important role in the proliferation and differentiation of blood cells.