Macrophage colony stimulating factor-induced differentiation of human cord blood monocytes into IL-10(high)IL-12(absent) dendritic cells with tolerogenic potential and into a rare population of CD16(+) monocytes

Tolerogenic dendritic cells (DCs) play an extremely important role in establishing immune tolerance. However, it is not clear how they develop in vitro and in vivo. The aim of this study was to identify a differentiation pathway of DCs with tolerogenic potential in vitro and to characterize their migration capacity. Granulocyte-macrophage (GM)- colony stimulating factor (CSF), combined with interleukin (IL)-4 or IL-4/transforming growth factor (TGF)-beta1 induces monocyte differentiation into DCs. Macrophage (M)-CSF is critical for the monocytic lineage, its level is dramatically elevated in immunosuppressive conditions, and M-CSF deficient mice are osteopetrotic. We hypothesized that M-CSF might be involved in generation of a novel subtype of suppressive DCs which may be capable of migrating into places where a non-efficient immune reaction occurs, such as tumour stroma, placenta and bone marrow. As SDF-1 is expressed in the above places, we hypothesized that M-CSF-induced suppressive DCs might respond chemotactically to SDF-1. Highly purified umbilical cord blood (CB) monocytes cultured in the presence of M-CSF and IL-4 differentiated, in a GM-CSF-independent fashion, into IL-10 highIL-12absent cells with heterogeneous morphology and DC phenotype. The addition of TGF-beta1 into M-DC cultures produced cells with a DC morphology. Single time stimulation with immature DCs derived from CB induced regulatory T cells. Mature M-DCs induced lower proliferation of naive CD4 T cells in both primary and secondary mixed lymphocyte reaction (MLR) than mature DCs and showed tolerogenic potential. Furthermore, TGF-beta-treated M-DCs expressed higher levels of surface CXCR4 than TGF-beta-treated DC and demonstrated enhanced responsiveness to SDF-1-induced chemotaxis. Beyond its role in DC differentiation, M-CSF in combination with IL-4 and IL-10 induced monocyte differentiation into CD14+CD16++ dendritic-like cells with a similar phenotype and function to that of the rare population of CD14+CD16++ monocytes present in vivo. CB monocytes were more responsive than adult blood (AB) monocytes to the effect of IL-10 on the generation of CD14+CD16 ++ cells. Together, our results demonstrate novel and multiple roles for M-CSF in the differentiation of suppressive DCs and CD14+CD16 ++ dendritic-like cells. This information is of relevance to efforts to induce bone marrow chimerism and/or tolerance during bone marrow transplantation and/or autoimmune diseases.