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Peripheral Leukocyte Subpopulations and Catecholamine Levels in Astronauts as a Function of Mission Duration

From the Departments of Psychiatry (P.J.M.) and Medicine (M.G.Z.), University of California, San Diego, La Jolla, CA; the Cardiovascular Laboratory (J.M.), Johnson Space Center, Houston, TX; and the National Space Biomedical Research Institute (W.W.W., D.D.), Baylor College of Medicine, Houston, TX.

Address reprint requests to: Paul J. Mills, PhD, UCSD Medical Center, 200 W. Arbor Dr., San Diego, CA 92103-0804. Email: pmills{at}ucsd.edu

OBJECTIVE: The objective of this study was to determine the effects of spaceflight duration on immune cells and their relationship to catecholamine levels.

METHODS: Eleven astronauts who flew aboard five different US Space Shuttle flights ranging in duration from 4 to 16 days were studied before launch and after landing.

RESULTS: Consistent with prior studies, spaceflight was associated with a significant increase in the number of circulating white blood cells (p < .01), including neutrophils (p < .01), monocytes (p < .05), CD3⁺CD4⁺ T-helper cells (p < .05), and CD19⁺ B cells (p < .01). In contrast, the number of CD3^-CD16⁺56⁺ natural killer cells was decreased (p < .01). Plasma norepinephrine levels were increased at landing (p < .01) and were significantly correlated with the number of white blood cells (p < .01), neutrophils (p < .01), monocytes (p < .01), and B cells (p < .01). Astronauts who were in space for approximately 1 week showed a significantly larger increase on landing in plasma norepinephrine (p = .02) and epinephrine (p = .03) levels, as well as number of circulating CD3⁺CD4⁺ T-helper cells (p < .05) and CD3⁺CD8⁺ T-cytotoxic cells (p < .05) as compared with astronauts in space for approximately 2 weeks.

CONCLUSIONS: The data suggest that the stress of spaceflight and landing may lead to a sympathetic nervous system–mediated redistribution of circulating leukocytes, an effect potentially attenuated after longer missions.

Key Words: spaceflight, • leukocytes, • lymphocytes, • catecholamines, • stress.

Abbreviations: NK = natural killer (cells);; SNS = sympathetic nervous system;; WBC = white blood cells.

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