Transferrin modulation of colony stimulating factor elaboration by adherent blood and bone marrow cells

When added to cultured normal, adherent blood and marrow cells at concentrations of 25-100 micrograms/ml (3 X 10(-7) to 1.3 X 10(-6) M), human transferrin enhanced colony-stimulating factor (CSF) elaboration. Fe saturated and relatively unsaturated Tf were equally effective in increasing CSF release, but soluble ferric nitriloacetate was ineffective. Dose-dependent increases in CSF release by adherent blood and marrow cells occurred in serum-free media and the continuous presence of Tf was necessary for this effect. Using a monoclonal anti-Tf receptor antibody, normal blood mononuclear cells contained no detectable Tf receptor positive cells. However, after 5 d culture in serum-free medium, Tf receptor positive cells were identified among normal adherent blood cells, and the per cent receptor positive cells increased with Tf concentration. We conclude Tf modulates CSF production from normal, adherent blood and marrow cells in vitro. These findings indicate a possible role for Tf in intramedullary regulation of normal granulopoiesis.