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Dendritic cells (DCs) are key players in immunity and tolerance. Some DCs express c‐kit, the receptor for stem cell factor (SCF), nevertheless c‐kit functional role and the regulation of its expression in DCs are incompletely defined. We recently demonstrated that autocrine SCF sustains a pro‐survival circuit, and that SCF increases phospho‐AKT in c‐kit+ mouse bone marrow‐derived DCs (BMdDCs). Herein we observed that CpG and PolyI:C, two stimuli mimicking bacterial and viral nucleic acids respectively, strongly inhibited c‐kit expression by BMdDCs and spleen DCs in vitro and in vivo. Experiments in IFNARI−/− mice showed that IFN‐I pathway was required for c‐kit down‐regulation in cDC1s, but only partially supported it in cDC2s. Furthermore, CpG and PolyI:C strongly inhibited c‐kit mRNA expression. In agreement with the reduced c‐kit levels, SCF pro‐survival activity was impaired. Thus in the presence of exogenously provided SCF, either PolyI:C or CpG induced spleen DC death in 2 days, while at earlier times IL‐6 and IL‐12 production were slightly increased. In contrast, SCF improved survival of unstimulated spleen DCs expressing high c‐kit levels. Our studies suggest that c‐kit down‐modulation is a previously neglected component of DC response to CpG and PolyI:C, regulating DC survival and ultimately tuning immune response. c‐kit down‐modulation is a previously neglected component of DC response to CpG and PolyI:C, regulating DC survival and ultimately tuning immune response. [ABSTRACT FROM AUTHOR]

Stem cell factor (SCF), the ligand of c-kit, is a key cytokine for hematopoiesis. Hematopoietic precursors express c-kit, whereas differentiated cells of hematopoietic lineage are negative for this receptor, with the exception of NK cells, mast cells, and a few others. While it has long been recognized that dendritic cells (DCs) can express c-kit, several questions remain concerning the SCF/c-kit axis in DCs. This is particularly relevant for DCs found in those organs wherein SCF is highly expressed, including the bone marrow (BM). We characterized c-kit expression by conventional DCs (cDCs) from BM and demonstrated a higher proportion of c-kit+ cells among type 1 cDC subsets (cDC1s) than type 2 cDC subsets (cDC2s) in both humans and mice, whereas similar levels of c-kit expression were observed in cDC1s and cDC2s from mouse spleen. To further study c-kit regulation, DCs were generated with granulocyte-macrophage colony-stimulating factor (GM-CSF) from mouse BM, a widely used protocol. CD11c+ cells were purified from pooled non-adherent and slightly adherent cells collected after 7 days of culture, thus obtaining highly purified BM-derived DCs (BMdDCs). BMdDCs contained a small fraction of c-kit+ cells, and by replating them for 2 days with GM-CSF, we obtained a homogeneous population of c-kit+ CD40hi MHCIIhi cells. Not only did BMdDCs express c-kit but they also produced SCF, and both were striking upregulated if GM-CSF was omitted after replating. Furthermore, a small but significant reduction in BMdDC survival was observed upon SCF silencing. Incubation of BMdDCs with SCF did not modulate antigen presentation ability of these cells, nor it did regulate their membrane expression of the chemokine receptor CXCR4. We conclude that the SCF/c-kit-mediated prosurvival circuit may have been overlooked because of the prominent use of GM-CSF in DC cultures in vitro, including those human DC cultures destined for the clinics. We speculate that DCs more prominently rely on SCF in vivo in some microenvironments, with potential implications for graft-versus-host disease and antitumor immunity. [ABSTRACT FROM AUTHOR]

Stem cell factor (SCF), the ligand of c-kit, is a key cytokine for hematopoiesis. Hematopoietic precursors express c-kit, whereas differentiated cells of hematopoietic lineage are negative for this receptor, with the exception of NK cells, mast cells, and a few others. While it has long been recognized that dendritic cells (DCs) can express c-kit, several questions remain concerning the SCF/c-kit axis in DCs. This is particularly relevant for DCs found in those organs wherein SCF is highly expressed, including the bone marrow (BM). We characterized c-kit expression by conventional DCs (cDCs) from BM and demonstrated a higher proportion of c-kit + cells among type 1 cDC subsets (cDC1s) than type 2 cDC subsets (cDC2s) in both humans and mice, whereas similar levels of c-kit expression were observed in cDC1s and cDC2s from mouse spleen. To further study c-kit regulation, DCs were generated with granulocyte-macrophage colony-stimulating factor (GM-CSF) from mouse BM, a widely used protocol. CD11c + cells were purified from pooled non-adherent and slightly adherent cells collected after 7 days of culture, thus obtaining highly purified BM-derived DCs (BMdDCs). BMdDCs contained a small fraction of c-kit + cells, and by replating them for 2 days with GM-CSF, we obtained a homogeneous population of c-kit + CD40 hi MHCII hi cells. Not only did BMdDCs express c-kit but they also produced SCF, and both were striking upregulated if GM-CSF was omitted after replating. Furthermore, a small but significant reduction in BMdDC survival was observed upon SCF silencing. Incubation of BMdDCs with SCF did not modulate antigen presentation ability of these cells, nor it did regulate their membrane expression of the chemokine receptor CXCR4. We conclude that the SCF/c-kit-mediated prosurvival circuit may have been overlooked because of the prominent use of GM-CSF in DC cultures in vitro , including those human DC cultures destined for the clinics. We speculate that DCs more prominently rely on SCF in vivo in some microenvironments, with potential implications for graft-versus-host disease and antitumor immunity.