Influence of in vivo hypobaric hypoxia on function of lymphocytes, neutrocytes, natural killer cells, and cytokines.

We have investigated the effects of short-term hypoxia in vivo on the human cellular immune system. Seven young healthy volunteers were placed in a decompression chamber (380 Torr) for 20 min with or without supplemental O2. The leukocyte concentration increased during hypobaric conditions because of an increased concentration of lymphocytes. The absolute and relative concentration of CD16+ natural killer (NK) cells increased markedly during hypoxia and returned to pretest values after 2 h of recovery. The NK cell activity of blood mononuclear cells (BMNC, %lysis/fixed no. of BMNC) boosted with interferon-alpha, interleukin-2 (IL-2), and indomethacin rose in parallel with unboosted NK cell activity during hypoxia. The percentage of CD4+ and CD8+ cells declined during hypoxia, whereas the absolute concentration of both CD8+ cells and CD14+ monocytes increased. Although the BMNC composition varied, the proliferative responses of BMNC after stimulation with phytohemagglutinin, purified derivative of tuberculin, and IL-2 did not change significantly. The in vitro production of interleukin-1 beta and IL-2 in supernatants obtained after stimulation of BMNC with phytohemagglutinin or lipopolysaccharide was not affected. The chemiluminescence response of neutrocytes increased 2 h after hypoxia. It was concluded that acute hypoxia induced marked alterations in the immune system and that the NK cells are especially sensitive to the hypoxic stimulus.