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.