Extended Space Flight Could Degrade the Immune System of Astronauts

NASA hopes to send humans to Mars by 2030 for a round – trip mission that could last up to three years – far longer than any human has ever traveled in the US. space. According to a new study by researchers at the University of Arizona, such long-term space flights could negatively affect some cells of the astronauts' immune system.

"NASA and other space agencies are worried about whether the immune system will be compromised during very long spaceflight missions," said Richard Simpson, senior author and badociate professor of nutrition sciences at l & # 39; AU. "What are the clinical risks to astronauts during these missions when they are exposed to problems such as microgravity, radiation and isolation stress? Could it be catastrophic to the point that 39, astronaut would not be able to carry out its mission?

Simpson and his team of researchers from the AU, the University of Houston, Louisiana State University and the NASA-Johnson Space Center have studied the effects of spaceflights of six months or more on NK cells , a type of white blood cell that kills cancer cells in the body and prevents old viruses from reactivating.

"Cancer represents a significant risk to astronauts during very long space flight missions due to radiation exposure," Simpson said. "[NK-cells] are also very important for killing cells infected with the virus. When you are in the space station, the environment is very sterile – you probably do not get the flu, a rhinovirus or a community-type infection – but the problematic infections are the viruses already in your body. system. 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 are reactivated when you are stressed. "

Scientists compared blood samples from eight crew members completing missions to the International Space Station with healthy individuals left on Earth. Blood samples were collected before launch, at several points during the mission and after the astronauts returned to Earth.

The results showed that NK cell function is altered in astronauts compared to pre-flight and ground control levels. At day 90, the cytotoxic activity of NK cells against leukemic cells in vitro was reduced by approximately 50% in crew members of the International Space Station.

"When we examine the function of airborne astronaut samples against their own pre-flight samples, it decreases, when we compare them to controls that have remained on Earth, the quality is still decreasing." said Simpson. "I think there is no doubt that the function of NK cells decreases in the environment of spaceflights when it is badyzed in a cell culture system."

The effect seems to be more pronounced in novice astronauts, as opposed to those who have already been in space.

"Fortunately, we found that half of our crew members had already flown, and the other half had not done so," Simpson said. "So we were able to divide them in half to see if there was an effect, and there was one." The "recruits" had larger declines in NK cell function compared to veterans. "

The differences could be categorized by age or stress, said Simpson, finding that novice astronauts, generally younger than their experienced counterparts, would find trips in the space more stressful than those who do not. had already done.

While declining NK cell function makes astronauts more vulnerable to cancer, it remains to be seen whether the virus will reactivate, making viral reactivation even more difficult, Simpson said. He hopes to learn more about future studies.

"The next question would be: how to mitigate these effects? How to prevent the immune system from degrading during space travel?" he said. "To do that, you first have to understand what causes the decline, it's stress, it's microgravity, it's the radiation, it's a plethora of things, and when you understand it you can try to find ways to directly target and mitigate these factors. "

Simpson and his colleagues at NASA-Johnson Space Center, as well as European and Russian scientists, are already working on potential countermeasures that could help keep astronauts healthy in space, including nutritional or pharmacological interventions and interventions. increased exercises, all of which have demonstrated their effectiveness. have a positive effect on the functioning of the immune system.

Studies have shown that spending long periods off the Earth presents certain health risks, such as the loss of muscle and bone due to the effects of microgravity. But scientists did not know if the unique conditions encountered by astronauts had had an impact on the immune system until now. The document, Spaceflight inhibits the function of NK cells, was published in the Journal of Applied Physiology.

Explore further:
Immune health in space

More information:
Austin B. Bigley et al., The function of NK cells is impaired during long-duration spaceflights, Journal of Applied Physiology (2018). DOI: 10.1152 / japplphysiol.00761.2018