In new research that delivers a blow to hopes of finding safe ways to send humans back to the moon or on to Mars, scientists have found that as little as a month in space can significantly depress the immune systems of mice, potentially making astronauts susceptible to ailments that their bodies would easily brush off on Earth.
But other research, published only a week before, suggests that other aspects of immune function might not suffer as badly from weightlessness as had previously been thought.
Scientists have been trying to unravel the health effects of space travel, and figure out ways to combat them, since at least 1966.
That’s when five Texas college students agreed to spend 20 days as the world’s ultimate couch potatoes. For three weeks, these previously active young men took to bed, not even getting up to walk to the toilet. NASA’s moon landings were looming, and prolonged bed-rest, medical researchers figured, was the best way to mimic the enforced inactivity of spaceflight.
What they found was disconcerting. When the young men finally staggered back to their feet, they were not only weak as kittens, but from a cardiovascular and exercise physiology standpoint, their bodies had (temporarily) deteriorated by the equivalent of several decades worth of ageing.
One side effect of this research was that doctors soon began prodding surgical patients out of bed at the earliest possible moment, rather than let them recuperate at a more leisurely pace. But from the standpoint of space travel, it was the first of a string of unpleasant discoveries.
Not only were moon- or Mars-bound astronauts at risk of obvious dangers such as radiation exposure or life support failures, but they were also subject to an array of health risks.
The most obvious of these relate to muscle atrophy and loss of bone density, which can, to some extent, be counteracted by specialised zero-gravity exercise programs.
But more recently, a new issue has come to the fore. Space travel may also compromise the immune system.
The most recent such finding appears today in the journal of the Federation of American Societies for Experimental Biology (FASEB). In it, a team of French and Russian scientists studied preserved bone marrow samples from mice that in 2013 had spent 30 days in weightlessness aboard Russia’s Bion-M1 satellite, which had carried them into orbit at an altitude of 575 kilometres (about the height of the Hubble Space Telescope).
The researchers found that a mere month of weightlessness altered bone marrow proteins involved in the production of B-lymphocytes, the white blood cells responsible for antibody production. The effect was strong enough that it persisted at least a week after the mice were returned to Earth.
Prior studies had shown that low gravity impaired other portions of the immune system, but this was the first time its effects had been studied in this detail on these critical cells.
Furthermore, says Fabrice Bertile, a biologist from the University of Strasbourg, France, who is lead author of the new study, the problem may not simply be a laboratory curiosity.
In 2016, Bertile says, a team from NASA’s Johnson Space Flight Centre in Houston, Texas, examined the medical records of 46 astronauts who had spent a total 20.57 years aboard the International Space Station.{%recommended 1739%}
“The data showed that 46 percent of them faced immunological problems,” he says.
These conditions, reported in 2016 in the International Journal of General Medicine, ranged from persistent skin rashes to prolonged congestion or nasal irritation, skin infections, cold sores, urinary tract infections, and allergic reactions. All were significant enough to be classified as “notable” as opposed to “minor” health events.
Guillaume Spielmann, an exercise immunologist at Louisiana State University, Baton Rouge, US, who was not part of the study team, calls Bertile’s study “really, really nice,” and a “beautiful paper”.
It’s also an interesting complement to Spielmann’s own work, which appeared last week in the Journal of Applied Physiology.
That study used blood samples from 23 astronauts, taken at several times before, during, and after six-month stints on the International Space Station.
“We had about nine time points per astronaut,” Spielmann says.
In addition to studying traditional measures of B-cell immune function, he says, his team measured “free light chains”, described in his paper as “near ‘real-time’ biomarkers of immunoglobulin synthesis”.
Immunoglobulins are the class of compounds that serve as antibodies.
Antibodies last long enough in the blood that their presence during spaceflight could be a carry-over from before launch. Free light chains, Spielmann says, have half-lives of only two to six hours, so their presence is a marker of at-the-moment immune system activity.
His team had expected the astronauts’ blood to display decreased numbers of B-lymphocytes and reductions in antibodies as their stints in space progressed. But that wasn’t the result. “We didn’t see much,” he says.
That said, he doesn’t think the two studies contradict each other. More likely, they are separate parts of a more complex puzzle.
“The main difference, besides the fact it’s mice and humans, is the time course,” Spielmann says.
“They used the Bion-M1, which is a biosatellite where you can just put animals in there, orbit for a month, and get back down. We had our astronauts for six months.”
Therefore, the mouse study might have found a transient effect in the bone marrow that didn’t translate to comparable changes in the bloodstream. This is particularly possible if the bone marrow changes were induced by stress, widely known to affect immune function. Humans at least know what’s going on when they are launched into space, find themselves in free-fall, then splash back to Earth.
And, “some of these effects could be associated with the landing, rather than the space flight per se,” Spielmann says.
In addition, the two studies looked at different portions of the immune process. Bertile’s examined what was going on at the cellular level inside the bone marrow. Spielmann’s looked at immune function in the blood.
Also, weightlessness is known to cause a reduction in bone marrow, much as it causes a reduction in bone density. To offset this, astronauts on the International Space Station use specialised equipment to exercise two hours a day.
“They do lose bone marrow, but not to the same extent,” Spielmann says. It is unlikely that the Bion-M1 mice were able to do the same.
Weightlessness, of course, isn’t the only factor that could affect the health of astronauts on a trip to Mars — nor is it the only one that could affect the immune system. Even if they know what’s going on, human space travellers will also experience substantial stress, if for no reason other than the fact that a Mars-bound crew will be confined in close quarters for an extended period of time.
Research has found that their immune systems could experience a triple whammy — one from the effect of weightlessness, another from the effect of social stresses, and a third from the fact that research has shown that not only do pathogens easily accumulate in the close confines of a spacecraft or space station, but exposure to space radiation appears to make these pathogens more virulent.
Traditional ways of countering this include pre-flight health screenings and quarantines to reduce the risk of astronauts carrying nasty pathogens with them into space.
Good sanitation during the trip can also help, says Bertile, including such simple measures as meticulous use of disinfectant wipes and wearing surgical masks if there is any sign of a respiratory infection. Vitamin D supplementation, and, of course, exercise, can also help, he says.
But Spielmann’s work also finds hope for another countermeasure.
Many people carry viruses such Epstein-Barr or varicella zoster, the virus that causes chickenpox in children … and which can return as shingles in adults.
“Once you get infected, you can’t really get rid of them,” Spielmann says. “[And] these are known to reactivate very heavily if you have high periods of stress or are immunocompromised” – which is exactly the sort of thing that can occur during a long space mission.
Coming down with shingles on a trip to Mars sounds like a special kind of hell.
But Spielmann says his research indicates that there may be a way to offset this risk. If the B-lymphocytes are actually producing the level of antibodies his research suggests they are, then it’s possible to carry vaccines with you on a trip to Mars and use them midway to stimulate the immune system to prevent latent viruses from re-emerging later in the trip.
“You can vaccinate an astronaut in transit and know they will remain protected,” he says.
It’s the type finding that indicates that even though space travel will always have health risks, the more we understand about them, the better are our chances of combatting them. If so, then maybe, eventually, we will someday watching Neil Armstrong’s one small step on the Moon become an even greater giant leap to Mars.
