Abstract: INTRODUCTION: Hypoxia is known to affect the immune system. It leads to an increase in pro-inflammatory cytokines such as interleukin-6 and influences the number of different inflammatory cells. This study investigates the effect of hypoxia on the number of different subsets of circulating human dendritic cells (DCs) as professional antigen-presenting cells. METHODS: The number of circulating DCs was determined via Fluorescence activated cell sorting analysis in peripheral blood of 17 healthy volunteers (age 35.9±2.6 years) in normoxia (baseline, BL), hypoxia (altitude 3000 m, alpine passive escalation), and again normoxia (follow-up, FU). RESULTS: Exposure to hypobaric hypoxia in high altitude, 3000 m, led to a significant decrease in the participants’ oxygen saturation, and an increase in the breathing frequency whereas blood pressure and heart rate were not significantly altered. FACS analysis revealed a significant hypoxia induced decrease in circulating plasmacytoid (p) DCs compared to baseline levels (BL: 0.10 [0.08–0.18] % of white blood cell count (WBC), 3000 m: 0.03 [0.02–0.06] % WBC, p < 0.001). During follow up, again a significant reconstitution of circulating pDCs was observed (FU: 0.16±[0.11–0.26] % WBC, p = 0.0013). CONCLUSION: Hypobaric hypoxia caused by exposure to altitude results in a significant reduction in the number of circulating pDCs.
