Space travel weakens astronauts' immune systems by altering gene expression
A new study has found that the rigors of space travel alter the expression of an astronaut’s genes, leading to a compromised immune system that may make them vulnerable to infection, especially when they first return to Earth.
Space is an extreme environment that can expose astronauts to all sorts of hazards, including health hazards. There is evidence that short- and long-term spaceflight has a negative effect on many physiological functions, due mostly to the transition to and from microgravity environments, which causes fluids to shift in the body.
Previous studies have looked at the impact of space flight on the body’s immune system. Even during the Apollo missions in the 1960s and ’70s, it was observed that just over half of the astronauts became sick with colds or other infections within a week of returning to Earth. With evidence suggesting that space travel weakens the immune system, researchers from the University of Ottawa, Canada, sought to understand what causes it.
The researchers studied gene expression in white blood cells (leukocytes) in 14 astronauts who resided on the International Space Station (ISS) for between four-and-a-half and six-and-a-half months between 2015 and 2019. Blood samples were taken from each astronaut at 10 points: once pre-flight, four times during flight, and five times when they were back on Earth.
They found 15,410 genes differentially expressed in leukocytes and, of these, identified two clusters that changed their expression along the timeline. Both gene clusters were mostly comprised of protein-coding genes, but there were differences between the two. The function of the first gene cluster was predominantly related to immunity, while the second was related to cellular structures and functions.
The researchers observed that the first cluster of genes dialed down when the astronauts reached space and went back up when they were on Earth; the reverse was seen for the second cluster.
“Here we show that the expression of many genes related to immune functions rapidly decreases when astronauts reach space, while the opposite happens when they return to Earth after six months aboard the ISS,” said Odette Laneuville, one of the study’s authors.
These results, say the researchers, indicate that space travel causes a rapid decrease in the immune system's strength.
“A weaker immunity increases the risk of infectious diseases, limiting astronauts’ ability to perform their demanding missions in space,” said Guy Trudel, another co-author. “If an infection or an immune-related condition was to evolve to a severe state requiring medical care, astronauts while in space would have limited access to care, medication, or evacuation.”
However, there was some good news from the study. The researchers found that most genes in both clusters returned to pre-flight levels of expression within a year of returning to Earth. Usually, this occurred within a few weeks. Nevertheless, say the researchers, it means that returning astronauts are at a higher risk of infection for about a month after they return home.
The researchers are unsure how long it takes for an astronaut’s immune system to return to full strength but they think it’s likely to depend on age, sex, genetic differences, and childhood exposure to pathogens.
The next step for the researchers is to develop measures to prevent space-induced immune suppression.
“The next question is how to apply our findings to guide the design of countermeasures that will prevent immune suppression while in space in particular for long-duration flight,” said Laneuville.
The study was published in the journal Frontiers in Immunology.