Innate Immune Phenotypes During Acute High-Altitude Exposure

We found several impacts of high altitude on immune cell populations, including shifts in monocytes from classical to intermediate (<i>p</i> = 0.004 after 1 night at high altitude [HA1], and <i>p</i> < 0.001 after 2 nights at high altitude [HA2]) and nonclassical subsets (<i>p</i> = 0.013 on HA2), and increases in total B cells (<i>p</i> = 0.001 on HA2, <i>p</i> = 0.004 [HA3]). An effect of altitude was found for neutrophil CD15 expression (<i>p</i> < 0.001), with a trend toward increased expression over time at high altitude. Higher Acute Mountain Sickness (AMS) scores on the second day at high altitude were associated with more pronounced shifts to nonclassical monocyte populations (<i>R</i>² = 0.79, <i>p</i> = 0.001). These data indicate that acute high-altitude travel results in a pro-inflammatory immune response, which may contribute to AMS. This response appears to blunt with acclimatization, although elevation in B cells remain by HA3.