Human monocyte-derived dendritic cells produce macrophage colony-stimulating factor: enhancement of c-fms expression...

Human monocyte-derived dendritic cells (DC) generated with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4 express c-fms (CD115), the receptor for macrophage-CSF (M-CSF). Expression of c-fms on monocyte-derived DC has been interpreted as the susceptibility of these cells to M-CSF-induced macrophage development. We show here that homogeneous cultures of CD14 DC constitutively produced large amounts of M-CSF. However, presence of M-CSF neither induced macrophage development nor did it prevent terminal maturation into CD83+ DC. M-CSF production by DC was driven by GM-CSF and inhibited by the specific phosphatidylinositol 3-kinase inhibitor wortmannin. M-CSF synthesis was rapidly induced during the first 24 h of DC culture and then declined during the 5-day culture period. Replating of the cells, which was associated by a transient adherence, always induced a strong up-regulation of M-CSF synthesis. Addition of recombinant IL-10 to DC cultures enhanced c-fms expression and induced macrophage development as measured by the strong up-regulation of CD14 expression as well as by enhanced expression of the Fcgamma receptors I, II, and III (CD64, CD32, CD16). Our data demonstrate that immature monocyte-derived DC produce M-CSF which does not induce macrophage development, despite the surface expression of c-fms on DC. IL-10 appears to induce macrophage development by up-regulating c-fms and, thereby, enhancing the sensitivity of the cells to endogenously produced M-CSF.