When the space shuttle Discovery lifts off on its final flight Nov. 2, its six astronauts will be joined by 16 rodent passengers on a historic mission of their own.
Riding in special self-contained modules that automatically supply them with food and water, the mice will be part of a long-term NASA effort aimed at understanding why spaceflight makes humans more vulnerable to infection by viruses and bacteria.
The agency has studied the phenomenon aboard its space shuttles for more than 25 years, collecting data from laboratory animals and astronauts themselves. The mouse experiment -- a collaboration between teams at the University of Texas Medical Branch at Galveston and NASA's Ames Research Center in Mountain View, Calif. -- will be the final immunology investigation planned for the shuttle program.
"Since the Apollo missions, we have had evidence that astronauts have increased susceptibility to infections during flight and immediately post-flight -- they seem more vulnerable to cold and flu viruses and urinary tract infections, and viruses like Epstein-Barr, which infect most people and then remain dormant, can reactivate under the stress of spaceflight," said Dr. Roberto Garofalo, a professor at UTMB Health and principal investigator for the project. "We want to discover what triggers this increased susceptibility to infection, with the goal both of protecting the astronauts themselves and people with more vulnerable immune systems here on Earth, such as the elderly and young children."
The mice aboard Discovery will be in orbit for 11 days, during which time shuttle astronauts will perform daily checks on their health and well-being. Within two hours of the shuttle's return to Earth, eight of the animals will be infected with respiratory syncytial virus -- a pathogen that infects almost all human children by age two and ordinarily causes a relatively harmless cold-like upper respiratory disease. In some children, however, the infection spreads to the lungs, where the inflammation it generates causes coughing, wheezing and extreme difficulty in breathing.
Another group of mice kept in nearly identical conditions on the ground will also be exposed to the virus. Garofalo's team will conduct genetic and protein studies of the lung and nasal tissues of both sets of mice, evaluating lung inflammation, viral replication and other key factors related to RSV infection in mice.
"We have substantial experience using mice to study immune response to RSV infection, and that will enable us to look at all the aspects of the immune responses of these mice as well as the pathological manifestations of the disease, looking at ways in which the space environment affects this respiratory infection," Garofalo said.
Understanding how spaceflight impairs the immune system and finding ways to make sure that infection doesn't threaten the health of space travelers are expected to become increasingly important, as NASA plans human expeditions beyond the relative safety of Earth orbit -- to Mars, for example, or the asteroids. The developing commercial spaceflight industry, which hopes to launch large numbers of private citizens into orbit in the near future, also has a stake in ensuring that its passengers stay safe and healthy.
Despite the shuttle program's end, Garofalo said, immune system experiments in space may well continue on the International Space Station.
"The space environment incorporates many factors that we know affect the immune system -- microgravity, radiation, even different nutritional standards -- all acting in a relatively short period of time," Garofalo said. "The space station provides a unique environment for generating answers to fundamental questions about the human immune system. Those answers will benefit people here on Earth, and there's been a lot of interest in pursuing them."
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