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

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.