Dendritic Cells and HIF Research into the role of HIF in DCs is complicated by the fact that DCs are a rare cell type and it is difficult to obtain adequate numbers of primary cells for experimentation. Consequently, much of the in vitro work on DCs and HIF has selleck products been performed on human peripheral blood monocytes or mouse bone marrow cells differentiated into DCs by treatment with granulocyte–macrophage colony stimulating factor (GM-CSF) and IL-4 for periods of 7–11 days. Both methods produce DCs most selleck chemicals similar
to iDCs , and not the migratory cDCs that are likely to play an important sentinel role in vivo. Previous attempts to determine the role of HIF in DC maturation have yielded contradictory results. Various investigators have produced data indicating that hypoxia promotes DC maturation both alone [51, 52], and in combination with LPS stimulus [53, 54], as measured
by decreased phagocytosis [55, 56], increased migration [57, 58], and increased expression of MHC and co-stimulatory molecules [54, 56, 57, 59]. Others have come to exactly the opposite conclusion, namely, that hypoxia inhibits DC maturation , migration [60, 61] (possibly by reducing expression of MMP-9, which helps DC migrate [62, 63]), and expression of co-stimulatory Omipalisib research buy molecules [60, 64, 65]. When it comes to the effect of hypoxia and HIF on the ability of APC to prime T cells, the literature is no less mixed. Some groups have shown that hypoxia and HIF increase the ability of APCs to stimulate a T-cell response [53, 56, 66, 67] and lead to the expression of more proinflammatory cytokines [53, 59, 60, 64, 65, 68, 69] that bias toward a TH1 response , and type I interferons , which are essential for the ability of DC to induce TH1 differentiation
. Others have found the opposite [55, 72]. Still others have reported a mixed phenotype among the DC in their in vitro model system . From the above literature survey, the jury is still out on the role of HIF in priming the enough adaptive immune response. Some of the variation in reported results may be due to differences in stimuli. Critically, the context within which HIF is activated (hypoxia versus inflammation) affects the results of HIF activation. When HIF is activated by hypoxia, it enhances transcription from a different set of target genes than when it is activated by a TLR ligand such as lipopolysaccharide (LPS) . Hypoxia and LPS stabilize HIF through different pathways; LPS-induced HIF stabilization requires both NF-κB and MyD88, while hypoxia-induced HIF stabilization is independent of NF-κB . Furthermore, when hypoxia is used as a stimulus in the antigen presentation readouts, it affects not only the APC but the T cells themselves, further influencing the results of the experiments.