THURSDAY, June 22, 2023 (HealthDay News) — Space travel appears to weaken astronauts’ immune systems, and researchers believe changes in gene expression are the culprit.

These immune deficits aren’t permanent. They disappear when back on Earth, often within weeks, according to new research published June 22 in Frontiers in Immunology.

“Here we show that the expression of many genes related to immune functions rapidly decreases when astronauts reach space,” said study lead author Dr. Odette Laneuville, an associate professor of biology at the University of Ottawa in Canada.

“The opposite happens when they return to Earth after six months aboard the ISS [International Space Station],” Laneuville added in a journal news release.

Astronauts seem more susceptible to infections in space, often getting skin rashes and a variety of other diseases on the ISS, evidence has suggested. They also shed, or emit, more live virus particles, including those for the Epstein-Barr virus; varicella-zoster, which is responsible for shingles; and herpes-simplex-1, the source of “cold sores.”

To delve into this, the researchers studied gene expression in leukocytes (white blood cells) in 14 astronauts. Among them were three women and 11 men living on the ISS from 4.5 to 6.5 months between 2015 and 2019.

The research team drew blood from each astronaut at 10 time points, including pre-flight, in flight and after their return to Earth.

The investigators found that 15,410 genes were differentially expressed in these white blood cells. The researchers identified two clusters among these genes, with 247 and 29 genes, respectively, that changed their expression in tandem during the studied timeframe.

The study showed that genes in the first cluster were dialed down when reaching space. Then they increased again when returning to Earth.

Genes in the second group followed the opposite pattern.

Both clusters mostly consisted of genes that code for proteins. Their predominant function was related to immunity for the genes in the first cluster, and to cellular structures and functions for the second cluster.

This suggests that during space travel these changes in gene expression cause a rapid decrease in the strength of the immune system.

This is an important finding, the researchers noted.

“A weaker immunity increases the risk of infectious diseases, limiting astronauts’ ability to perform their demanding missions in space. 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,” said Dr. Guy Trudel, a rehabilitation physician and researcher at the Ottawa Hospital.

Fortunately, these changes were transient, with most genes in both clusters returning to normal within a year of landing back on Earth, and often after only a few weeks, the study found. Returning astronauts appear to have an elevated risk of infection for at least one month after their return to Earth.

What isn’t clear is how long it takes before immune resistance is back to its pre-flight strength. That may vary based on age, sex, genetic differences and childhood exposure to pathogens, according to the study.

The Canadian Space Agency funded the research.

NASA has more on human health and space travel.

SOURCE: Frontiers in Immunology, news release, June 22, 2023