Research finds how astronauts’ immune systems in space are weakened

Researchers have revealed evidence of adverse effects on the human body when astronauts travel to space in a microgravity environment impacting their immunity and decreasing the activity of genes in white blood cells, Reuters reported.

During the study, experts observed 14 astronauts who spent 4-1/2 to 6-1/2 months on the International Space Station (ISS).

The finding revealed that gene expression in these cells, also called leukocytes, quickly reduced when they move out from Earth and then returned to normal as they come to their natural habitat, researchers said.

The study — published in the journal Frontiers in Immunology — provides crucial information about why space travellers are more prone to infections during flights, explaining how the human body’s ability to fight pathogens is less effective in space.

“A weaker immunity increases the risk of infectious diseases limiting astronauts’ ability to perform their very demanding work 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 and medication,” said the lead author of the study Odette Laneuville of the University of Ottawa in Canada.

Leukocytes are formed in the bone marrow and are responsible for protecting humans from outside infections by producing antibody proteins and certain genes regulate the release of such proteins.

The study found that gene expression in 247 genes in leukocytes was at about one-third of the normal levels while in space.

This happened within the first few days in space but then remained at a stable level. The genes typically returned to normal behaviour within about a month of an astronaut’s return to Earth.

“White blood cells are very sensitive to the environment of space. They trade their specialized immune functions to take care of cell maintenance or housekeeping roles. Before this paper, we knew of immune dysfunction but not of the mechanisms,” said co-author Guy Trudel, an Ottawa Hospital rehabilitation medicine specialist.

Discovering altered gene behaviour in leukocytes is “a significant step toward understanding human immune dysregulation in space,” Trudel added.

This altered behaviour, the researchers said, may result from a phenomenon called “fluid shift” in which blood in the absence of Earth’s gravitational pull is redistributed from the lower to the upper part of the body. It is unlikely that greater solar radiation exposure in space was the culprit, they added.

“New and specific countermeasures will be needed,” Trudel said.

Scientists previously documented astronauts experiencing immune dysfunction in space which included the reactivation of latent viruses such as Epstein-Barr, responsible for infectious mononucleosis; varicella-zoster, responsible for shingles; and herpes simplex 1, responsible for cold sores.

It also has been shown that astronauts in space shed more viral particles in their biological fluids — saliva and urine — increasing the risk of spreading pathogens to fellow astronauts whose own immune systems may be weakened.