The Highlighted Topics' Selected Contributions for this issue of the Journal of Applied Physiology are a set of companion articles that report immunologic responses of C57BL/6 mice flown for 12 days aboard the Space Shuttle Endeavor (STS-108/UF-1, December 2001). There are several aspects of the spaceflight environment that can lead to changes in immunity: mission-related psychological stress, launch and landing conditions (acceleration, vibration, and acoustic), low-dose/low-dose-rate radiation, and changes in gravity. In the first Highlighted Topics article featured in this issue of the Journal of Applied Physiology,“Effects of spaceflight on immunity in the C57BL/6 mouse. I. Immune population distributions,” Pecaut et al. report that exposure to the spaceflight environment leads to shifts in immunocyte population distributions in blood, spleen, and bone marrow. The changes reported were more consistent with shifts in bone marrow hematopoiesis rather than a response to isolated changes in the periphery. In the second article featured in this issue, “Effects of spaceflight on immunity in the C57BL/6 mouse. II. Activation, cytokines, erythrocytes, and platelets,” Gridley et al. report changes in total body and organ masses, lymphocyte activation, cytokine expression, and hematological parameters. Two of the most striking findings were spaceflight-induced reductions in interleukin-2 (i.e., a cytokine that is critical for immune defense against virus-infected, tumor, and other aberrant cells) and the development of anemia.
Although the immunologic responses to spaceflight are important and interesting in themselves, probably more significant is that this represents the first time that the C57BL/6 mouse model was utilized to examine responses to the spaceflight environment. Although the rat model has been in orbit on over 20 occasions (with many articles published in the Journal of Applied Physiology), it has been a considerable challenge to approve the use of mice in the animal enclosure module (NASA Ames Research Center), which is currently the only operational, flight-qualified animal habitat. This is largely because of astronaut concerns with the odor produced by mice. Considering the confined, closed environment of an orbiting space shuttle, this is an understandable constraint. However, the benefits of utilizing mice for space experimentation are obvious to those involved in such work. Compared with previous flight models (rats and monkeys), mice require less of valuable shuttle resources (i.e., food, water, mass; crew time; and oxygen and carbon dioxide scrubbing capacity). Furthermore, because of their diminutive nature, there is an option for greater statistical sample size. Although these practical advantages are certainly worth noting, the primary scientific benefit for sending mice into space is the option to examine the interaction between various aspects of the spaceflight environment and specific genotypes. Because the C57BL/6 mouse is a common background for several genetic models, the success of this initial flight has opened the door for future studies utilizing transgenic and knock-out strains. This asset is of heightened relevance with the recent completion of the mapping of the mouse genome and its remarkable similarities with the human genome. Microarray technology has made genome-wide analysis practical. The ability to examine in vivo gene expression changes caused by the spaceflight environment has tremendous potential to help determine the molecular basis for the physiological adaptations caused by microgravity, potentially aiding in the development of countermeasures for these changes in astronauts. These advantages will only improve with the predicted wave of proteomic technologies.
- Copyright © 2003 the American Physiological Society