Space travel takes a heavy toll on the human body, a new study published in Nature Communications reveals. Researchers collected data from the two men and two women who orbited Earth during the 2021 SpaceX Inspiration4 mission. They discovered that the immune system went haywire, triggering inflammatory responses and creating chaos at the cellular level.
The study found evidence that a high-altitude, three-day spaceflight induces the production of known cytokine signatures as well as previously undocumented cytokines. Cytokines are substances secreted by the immune system that play critical roles in immune response and muscle regulation. Some of the cytokines found are normally associated with exercise, known as exerkines, produced by muscle and other tissues.
The scientists explored whether muscle tissue could be the source of these immune markers and found significant increases in several myokines, proteins produced by skeletal muscle cells. This increase seems to represent “a physiological response to microgravity” rather than a purely immune response. Blood collected before and after the mission showed cell- and sex-specific responses to spaceflight.
Noteworthy was an increase in several pro-inflammatory molecules like Interleukin 6 and MCP-1, but no significant changes in fibrinogen and hemoglobin levels.
Immune challenges in space missions
To understand spaceflight’s impact on different cell types, scientists examined changes at the cellular level and found an increase in B-cell receptor mutations, usually caused by inflammatory stimuli or antigen exposure.
Despite this, B-cells, which produce antibodies, appeared more active post-flight. The study highlighted gender differences, indicating women might be more resilient to the stresses of space travel and recover more quickly. The ratio of up- and down-regulated differentially expressed genes (DEGs) was higher in males, suggesting a higher number of altered gene expression pathways in males.
Differences were also noted in levels of Interleukin 8 and fibrinogen, important for inflammatory response and blood clotting, respectively. While these findings have important implications, especially for crew selection for future space missions, the scientists cautioned that their sample size of four astronauts is small. Further research, including data from additional missions, is necessary to validate these findings.
Additional information comes from NASA’s Twins Study, which examined identical twin astronauts Scott and Mark Kelly. Scott spent 340 days in space, while Mark remained on Earth. The study provided insights into how space travel affects gene expression and health.
In conclusion, while space travel poses significant challenges to the human body, these findings are crucial for developing countermeasures and monitoring astronauts’ health during long-duration space missions.
