NASA uses land model to test stress of space flight on immune systemIt lays claim to being the coldest, driest, windiest continent on Earth. It also is the world's highest and most isolated continent. Not sterling characteristics to attract the casual continent hopper. But for stalwart National Aeronautics & Space Administration scientists and their Australian collaborators, Antarctica offers an enticing land-based analog to space flight and a near-perfect laboratory for studying the stress-inducing effects of confinement and isolation on human health.NASA stress-related research is being carried out at Mawson, Davis, and Casey, three rocky outcrops on the edge of Antarctica's ice plateau, some 2,170 to 3,410 miles from Hobart, Tasmania. These stations are staffed year-round by personnel from the Australian Antarctic Division, which has been studying the continent's biology, geology, glaciology, climate, human impacts, and human biology for more than 50 years. Stress-related research is carried out at three outposts on Antartica
NASA selected the Australian stations over the one operated by the U.S. National Science Foundation at McMurdo because they are physically isolated once the last ship leaves at the end of the austral summer. McMurdo has a landing strip that allows for emergency evacuations year-round. The Australian sites lack airstrips and no ships can reach the researchers during their winter iced-in hiatus.
So, for eight to nine months, the 15 to 20 hardy souls who overwinter at each station "are isolated from other humans and that tends to create additional stress," explains Duane L. Pierson, director of microbiology at NASA's Johnson Space Center in Houston. Their only communication with the outside world is by satellite phone, fax, and e-mail. All medical and dental emergencies are treated by the one physician stationed at each site. The harsh winter environment compounds the stress of isolation: Temperatures can hover around -40 °C, humidity is very low, howling blizzards blow up to 90 knots, and darkness reigns for 20 or so hours a day. Apart from the scientists and their support staff, the only animal or insect species inhabiting the continent in the winter are penguins and mites, says Desmond J. Lugg, head of polar medicine for the Australian Antarctic Division. Lugg has been involved in Antarctic expeditions since 1962, when he spent 15 months at Davis. He serves as NASA's contact for all joint U.S.-Australian biomedical studies related to space flight. Augmenting the stressors imposed by the environment and by the isolation is the psychological stress of being cooped up in fairly close quarters with a group of people for up to nine months. Psychological studies of scientists and support staff who have overwintered on Antarctica over the past four years bear this out. Isolation per se is not particularly stressful, says JoAnna Wood, a senior scientist for Wyle Labs, Houston, who is working in NASA's psychology and behavior lab, but "interpersonal tensions" are. Lugg's polar medicine group-using themselves as guinea pigs-has been compiling baseline immunological data, which NASA realized it could tap into for its own space flight applications. Since 1993, Pierson and Lugg have been collaborating on a variety of microbiological studies, most recently the role stress plays in the reactivation of latent viruses such as herpesvirus. More than 90% of the world is infected with at least one herpesvirus, and once these viruses have invaded cells they can lay dormant for years. Then something like stress will trigger their reactivation. "No one understands all the molecular aspects of viral latency, but it is believed that the cellular immune system keeps viruses in check," explains Pierson. So he is using viral activation (shedding) as an indicator of changes in the cellular arm of the immune system. Pierson's group is tasked with ensuring that microorganisms do not harm the health, safety, or performance of astronauts-a unique, exceptionally healthy population. But astronauts are exposed to a variety of stresses, not the least of which is sitting on top of a controlled explosion at takeoff. On Earth, stress triggers the reactivation of latent viruses while causing a cascade of changes by the neuroendocrine system that affects the performance of the immune system. Whether this occurs in space flight is not yet firmly established. In the few studies that have been done, "we don't see a high incidence of illness from infections" during or following space flights, Pierson says. Still, urine and saliva samples collected before launch and after landing indicate that viral shedding occurs during flight. But there is not an increased level of shedding, at least "not enough to cause infection or, perhaps, compensatory mechanisms came into play to prevent infection," he adds.
Earlier NASA in-flight studies have documented a decrease in cell-mediated immune function. The part of the immune system that produces antibodies, the humoral arm, is currently being studied, according to Clarence F. Sams, director of cellular/molecular research laboratories, and Pierson's colleague at the Johnson Space Center. It is too early to know whether the viral shedding and depression of the cellular immune system have any clinical relevance-whether they are sign posts on the road to illness. The data were collected from short-duration shuttle flights, and "most parameters bounce back to normal within days after landing," Sams says. Both Pierson and Sams, however, are concerned that the risk of infectious disease could increase for long-duration missions. A Mars mission, for example, could take 30 months. As Pierson explains, the already observed decline in cell-mediated immune function on short flights could translate to an increased reactivation of herpesvirus. And this could translate to an increase in "the incidence and the duration of viral shedding"- and an increase in infections. If the cellular immune system is compromised, it could portend ill for the astronauts. Shedded viral particles are large and in the microgravity of space flight would not settle out. The space vehicle requires crew members to live in fairly crowded conditions and to breathe and drink recycled air and water-ideal conditions for the transfer of viruses from one crew member to another. Pierson proposes that the stress of long-duration flight will increase the frequency and duration of latent virus reactivation and the shedding of these viruses to urine, feces, and saliva. But testing his hypothesis in flight is difficult because space is limited and refrigeration typically is not available onboard to preserve collected samples. Because Lugg's group had already documented decreases in the cellular immune system triggered by the psychological stress of overwintering in Antarctica, Pierson decided to use the mainly Australian scientists and support staff who overwinter in Antarctica to verify his thesis. Baseline urine and saliva samples of the Antarctic expeditioners are taken several weeks before their isolation period. During the course of their overwinter confinement, expeditioners collect small saliva and urine samples every other day. These are stored frozen and, at the end of winter, shipped to NASA's Johnson Space Center for viral DNA analyses. After extracting the DNA, Pierson analyzes for the Epstein-Barr virus (mononucleosis), herpes simplex 1 (fever blisters), and cytomegalovirus (retinitis in immunosuppressed populations) using the polymerase chain reaction. Data collected to date seem to validate Pierson's hypothesis. "Preliminary results indicate that viral shedding appears more frequently in the expeditioners than in most healthy individuals," Pierson tells C&EN. Return to article |
