Changes in neutrophil functions in astronauts
Introduction
Astronauts live and work in a relatively crowded and stressful environment. Stresses integral to space flight, such as containment, isolation, space radiation, physical exertion, psychosocial conflict, anxiety, and sleep deprivation, can adversely affect astronaut health. A general consensus suggests that stress effects are likely to increase as mission duration and mission activity demands and complexities increase (Taylor et al., 1997). Studies of space flight and the human immune response have shown changes in lymphocyte proliferation (Konstantinova et al., 1993), phenotypes of peripheral blood mononuclear cells (Meehan et al., 1992; Taylor et al., 1986), cytokine production (Berry et al., 1991; Konstantinova et al., 1993; Sonnenfeld et al., 1990), natural-killer cell cytotoxicity (Konstantinova et al., 1993; Mehta et al., 2001), cell-mediated immunity (Konstantinova et al., 1993; Taylor and Janney, 1992), and other aspects of immune function (Taylor et al., 1997). However, the effects of spaceflight on phagocytic, degranulation, and oxidative functions of neutrophils have not been previously reported.
Neutrophils are important elements of astronaut health, and increases in the number of neutrophils of more than 100% after space flight have been reported (Taylor et al., 1997). Stowe et al. (1999) were first to report changes in neutrophil function after space flight by demonstrating alterations in neutrophil chemotaxis and adhesion to endothelial cells in astronauts following short-duration space flights.
Understanding the effects of space flight on the human immune response is essential to ensure the health, safety, and performance of space station crewmembers. As crewmembers are now continuously occupying the International Space Station, it is essential to understand the possible effects of stress associated with space flight on the immune system. This study was undertaken as part of astronaut health assessment and specifically examined the basic functions of neutrophils necessary to meet invading microbial challenges.
Section snippets
Subjects
Twenty-five astronauts from four space shuttle missions of 5- to 11-day duration were subjects for this study. The crew of the 5-day mission consisted of three males and two females in the age group of 44.8 ± 5 years. The crew of the longer missions (9-, 10-, and 11-day duration) consisted of 14 males and 6 females, with 19 of them in an age group of 41.9 ± 4.8. One crewmember was 77 years old. Nine healthy subjects, 8 males and 1 female, in an age group of 48.5 ± 4 years were included as a control
Results
When the phagocytic and oxidative burst functions of neutrophils from the astronauts were compared to those functions of the control subjects, we found that neutrophils from the astronaut samples of the 5-day mission performed similarly to those of the controls. Thus, samples from the control subjects, the astronauts from the 5-day mission, and the astronauts from the 9- to 11-day missions were grouped separately for analysis.
Discussion
Spaceflight, along with preflight preparations, represent a complex and stressful environment. Some of the stresses that astronauts experience are found in stress models found on earth. These may include anxiety, fear, isolation, containment, psychosocial issues, physical exertion, sleep deprivation, increased radiation levels, and microgravity. Astronauts may continuously or intermittently experience some or all of these stresses, making spaceflight a unique stress environment. However, many
Acknowledgements
The authors extend their appreciation to the astronauts and control subjects for participating in this study. We thank Dr. Gary Hudson of SPSS Inc. and Dr. Alan H. Feiveson of the Johnson Space Center for their suggestions in the statistical analysis of the data, Dr. Jane Krauhs of Wyle Life Sciences for editing the manuscript, and Sharon K. Jackson of Wyle Life Sciences for her assistance with preparation of the manuscript. We thank NASA for providing funding through NRA 111-30-10-06 to
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