Space travel is proving to have more profound impacts on the human body than initially anticipated, with new research indicating its substantial effects on the immune system through alterations in gene activity within white blood cells, or leukocytes. These findings could shed light on the heightened vulnerability of astronauts to infections during their time in space, due to a weakened defense system against pathogens.
A research team, led by molecular biologist Odette Laneuville of the University of Ottawa in Canada, studied 14 astronauts from the Canadian Space Agency and NASA who had spent between 4.5 to 6.5 months on the International Space Station. The study, published in the journal Frontiers in Immunology, observed that gene expression in leukocytes diminished rapidly in space but returned to regular levels shortly after the astronauts returned to Earth.
Leukocytes, manufactured in the bone marrow and dispersed throughout the body via the bloodstream and tissues, have the critical role of identifying and attacking foreign invaders such as bacteria and viruses by producing antibody proteins. Specific genes are responsible for the release of these proteins.
The researchers examined leukocytes in blood samples taken from the astronauts before, during, and after their space missions. They discovered that gene expression in 247 genes within the leukocytes was reduced to about one-third of regular levels during their time in space. This reduction occurred within the first few days in space, and these levels remained consistent throughout the mission.
Remarkably, these genes generally resumed their typical behaviour within a month after the astronauts returned to Earth. According to study co-author Guy Trudel, a rehabilitation medicine specialist at Ottawa Hospital, these findings represent a “significant step toward understanding human immune dysregulation in space.”
The researchers speculated that this altered behaviour could be due to a phenomenon called “fluid shift,” which results from blood being redistributed from the lower to the upper part of the body in the absence of Earth’s gravitational pull. They deemed it improbable that increased solar radiation exposure in space was the primary cause.
The implications of these findings are significant, especially considering that astronauts have been previously documented to experience immune dysregulation in space, including reactivation of latent viruses and increased shedding of viral particles in biological fluids. This presents an increased risk of pathogen transmission among astronauts, who may all be experiencing weakened immune systems.
This research follows another recent study detailing how space travel impacts brain structure, with astronauts experiencing an expansion of fluid-containing spaces in the brain. Other documented physiological effects of space travel include bone and muscle atrophy, cardiovascular changes, balance system issues in the inner ear, eye-related syndromes, and increased cancer risk from radiation exposure. These findings collectively emphasize the need for specific countermeasures to protect astronauts’ health in the challenging environment of space.
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