Modulation of chemokine receptor expression and functions by hypoxia. Human monocyte–derived DCs were cultured for 18 hours under normoxic or hypoxic conditions in the presence or absence of LPS and analyzed for their chemotactic responsiveness and chemokine receptor expression. (A) Effects of hypoxia on the chemotactic responsiveness of monocyte-derived DCs toward CXCR4-, CCR5-, and CCR7-specific ligands, CXCL12/SDF-1, CCL5/RANTES, and CCL19/ MIP-3β, respectively. DCs were cultured for 18 hours in the indicated conditions, and the migration assay was performed using a chemotaxis microchamber. Chemokines were used at 100 ng/mL. Data are means plus or minus SD of 3 independent experiments done in triplicate. *P < .05 versus normoxic counterparts. (B) Flow cytometric analysis of chemokine receptor surface expression of monocyte-derived DCs. DCs were stained with CXCR4-APC, CCR7-PE-Cy7, CCR5 + Alexa488, and isotype-matched antibodies (isotypic control). Results are means plus or minus SD of 3 independent experiments. *P < .05 versus normoxic counterparts. (C,D) Effects of hypoxia on human myeloid DCs isolated from peripheral blood. CD1c⁺ myeloid DCs were cultured for 18 hours under normoxic or hypoxic conditions in the presence or absence of LPS. (C) In CD1c⁺ myeloid DCs isolated from blood, LPS-induced TNFα secretion was enhanced in hypoxia, while low oxygen tension reduced IL-10 and CXCL10 secretion. Furthermore (D), hypoxia promoted a strong decrease of CCR7 surface expression, partial reduction of CD40, CD83, MHC class II, and significant up-regulation of CXCR4. Numbers on top of bars show mean fluorescence intensity.