Long-term spaceflights—like those to Mars—could harm certain cells in astronaut immune systems, especially for those traveling to space for the first time, researchers warn.
“What NASA and other space agencies are concerned about is whether or not the immune system is going to be compromised during very prolonged spaceflight missions,” says Richard Simpson, associate professor of nutritional sciences in the College of Agriculture and Life Sciences at the University of Arizona.
“What clinical risks are there to the astronauts during these missions when they’re exposed to things like microgravity, radiation, and isolation stress? Could it be catastrophic to the level that the astronaut wouldn’t be able to complete the mission?”
Shingles, mono, and cold sores
For the new study in the Journal of Applied Physiology, researchers looked at the effects of spaceflights of six months or more on natural killer cells, or NK cells, a type of white blood cell that kills cancerous cells in the body and prevents old viruses from reactivating.
“Cancer is a big risk to astronauts during very prolonged spaceflight missions because of the exposure to radiation,” Simpson says. “NK cells are also very important to kill off virally infected cells.
“When you’re in the space station, it’s a very sterile environment—you’re not likely to pick up the flu or a rhinovirus or some community-type infection—but the infections that are a problem are the viruses that are already in your body. These are mostly viruses that cause things like shingles, mononucleosis, or cold sores; they stay in your body for the rest of your life, and they do reactivate when you’re stressed.”
Scientists compared blood samples of eight crew members who completed missions to the International Space Station with healthy individuals who remained on Earth. Scientists took blood samples before launch, at several points during the mission, and after the astronauts’ return to Earth.
The results show impaired NK-cell function compared with pre-flight levels and ground-based controls. At flight day 90, NK-cell cytotoxic activity against leukemia cells in vitro dropped approximately 50 percent in International Space Station crew members.
“When we look at the function of the astronaut samples during flight compared to their own samples before they flew, it goes down. When we compare them to controls who stayed on Earth, it still goes down,” Simpson says. “I don’t think there’s any doubt that NK-cell function is decreasing in the spaceflight environment when analyzed in a cell culture system.”
The effect appears to be more pronounced in first-time astronauts, as opposed to those who have already been in space.
“Serendipitously, we found that half our crew members had flown before, and the other half hadn’t,” Simpson says. “So we were able to just split them in half to see if there was an effect, and there was. The ‘rookies’ had greater drops in NK-cell function compared to the veterans.”
Age or stress could cause the difference, Simpson says. Rookie astronauts, who are generally younger than their veteran counterparts, may find space travel more stressful than veteran astronauts.
Whether the drop in NK-cell function makes astronauts more susceptible to cancer and viral reactivation is unclear, Simpson says. He hopes to learn more from future studies.
“The next question would be, how do we mitigate these effects? How do we prevent the immune system from declining during space travel?” he says. “In order to do that, you have to first figure out what’s causing the decline: Is it stress? Is it microgravity? Is it radiation? Is it a plethora of things? When we figure that out, we can try to find ways to directly target those factors and mitigate them.”
Simpson and his fellow researchers at NASA Johnson Space Center, along with European and Russian scientists, are already working on potential countermeasures that could help keep astronauts healthy in space, including nutritional or pharmacological intervention and increased exercise, all of which have a positive effect on immune system function.
Additional collaborators on the work are from the University of Arizona, the University of Houston, Louisiana State University, and the NASA Johnson Space Center. NASA and the National Space Biomedical Research Institute’s (NSBRI) First Award Program funded the work.
Source: University of Arizona