Operation Everest II: alterations in the immune system at high altitudes

Area of Science:

• Aerospace Medicine
• Immunology
• Environmental Physiology

Background:

• Understanding immune system responses to extreme environments is crucial for astronaut health and high-altitude adaptation.
• Hypobaric hypoxia, a condition of reduced oxygen pressure at high altitudes, presents a significant environmental stressor.
• Previous research has indicated potential immune dysregulation under hypoxic conditions, but comprehensive human studies are limited.

Purpose of the Study:

• To investigate the impact of progressive hypobaric hypoxia simulating a 4-week ascent to 25,000 ft on human immune function.
• To assess both in vitro and in vivo immunological variables at various simulated altitudes.
• To elucidate the specific effects on T-cell activation, B-cell function, and mucosal immunity.

Main Methods:

• Subjects underwent simulated ascent to 7,500 ft and 25,000 ft in a decompression chamber.
• In vitro immune assays included phytohemagglutinin-stimulated thymidine uptake, protein synthesis, and mitogen-stimulated immunoglobulin secretion from mononuclear cells.
• In vivo assessments included mononuclear cell subset analysis, plasma immunoglobulin levels, interferon production, natural killer-cell cytotoxicity, and mucosal immune markers.

Main Results:

• Phytohemagglutinin-stimulated thymidine uptake and protein synthesis in mononuclear cells were reduced at extreme altitudes.
• Mononuclear cell analysis showed an increase in monocytes but no significant changes in T-cell or B-cell subsets.
• Plasma IgM and IgA levels increased, while T-cell activation appeared blunted, contrasted by preserved B-cell function and mucosal immunity.

Conclusions:

• Severe hypobaric hypoxia at 25,000 ft appears to blunt T-cell activation in humans.
• B-cell function and mucosal immunity (IgA, lysozyme) remain largely unaffected by simulated high-altitude exposure.
• Hypoxia may induce alterations in immune regulation, impacting effector-cell function, though mechanisms require further elucidation.