The glucocorticoid dexamethasone programs human dendritic cells for enhanced phagocytosis of apoptotic neutrophils and inflammatory response

GCs are powerful anti-inflammatory compounds inhibiting inflammatory cell recruitment and production of proinflammatory cytokines. We have recently found that DCs, the key players of T cell priming and polarization, respond to allogeneic apoptotic neutrophils with proinflammatory cytokine release and Th1 cell activation. Here, we show that monocyte-derived human DCs develop their capacity to engulf apoptotic cells by up-regulating a set of apoptophagocytic genes. This gene expression pattern was reprogrammed when differentiation took place in the presence of the synthetic GC Dex, which increased the expression of phagocytosis receptors MERTK and CD14, the bridging molecule C1QA, DNASE2, and ADORA3. The increased phagocytosis was attenuated by the addition of ADORA3 antagonist and could not be observed when bone marrow-derived DCs of ADORA3 KO mice were treated with Dex. The GC-treated human DCs loaded with allogeneic apoptotic neutrophils secreted, in response to LPS and IFN-γ, the inflammatory cytokine TNF-α. Furthermore, the Dex-treated DCs could activate autologous T lymphocytes toward Th1 effector cells, and this was enhanced by their exposure to allogeneic apoptotic neutrophils.