Why space travel weakens our immune systems?

The final study by the UCSF astronaut points to Treg cells as the culprit.


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A deep understanding of human immune adaptations to microgravity is a necessary step to design data-driven interventions aimed at preserving astronauts’ immune defense during short- and long-term spaceflights.

The observations from Apollo missions suggest that astronauts became sick with colds or other infections within a week after returning from space. Some astronauts have also experienced reactivation of dormant viruses, such as the chickenpox virus.

For decades, scientists have been exploring the effects of microgravity on the immune system, sometimes by simulating space gravity in earthbound labs.

In the latest study by one of the first women astronauts, Millie Hughes-Fulford, Ph.D., scientists at UCSF and Stanford University have found that the weakening of an astronaut’s immune system during space travel is likely due in part to abnormal activation of immune cells called T regulator cells (Tregs).

Tregs are usually triggered to dampen the immune response when the threat of infection is no longer there. They are also essential regulators of immune responses in diseases ranging from cancer to COVID-19.

In microgravity conditions, the scientists discovered changes in Tregs that enable them to go to work even before the immune system was tested. When they invigorated a resistant reaction in invulnerable human cells from blood tests in microgravity, with a chemical regularly utilized in examination to imitate a disease patoen, they found that Tregs helped the immune response was triggered.

Jordan Spatz, Ph.D., a space scientist and UCSF medical student who became co-PI of the study after Hughes-Fulford’s death, noted that “as space travel becomes increasingly commercialized and more common, concerns over the health status of space travelers are likely to grow.”

“Early in the space program, most astronauts were young and extremely healthy, but now they tend to have much more training and are older. In addition, apart from astronauts, with the commercialization of space flight, there will be many more older and less healthy individuals experiencing microgravity. From space medical perspective, we see that microgravity does a lot of bad things to the human body, and we are hoping to gain the ability to mitigate some of the effects of microgravity during space travel.”

In an earlier study, Hughes-Fulford had found weaker responses from T lymphocytes of the immune system, some of which attack specific pathogens directly, some of which help orchestrate the immune response. Also, it was found that natural killer lymphocytes were less active under simulated microgravity. In addition, antibody-producing B cells appeared to be unaffected.

This new study advances findings from experiments in space and simulated microgravity while contributing additional molecular discoveries.

Using a long-established microgravity research tool, scientists simulated microgravity in blood samples. The tool was a specialized, cylindrical, cell-culture vessel with motor-driven rotation. Scientists ten determined individual immune cells by specific type. They used metal tags and mass spectroscopy to simultaneously detect and quantify dozens of proteins that play a role in immune function.

They also confirmed previously identified patterns of altered gene activation.

Journal Reference:
  1. J. M. Spatz et al., Human immune system adaptations to simulated microgravity revealed by single-cell mass cytometry, Scientific Reports (2021). DOI: 10.1038/s41598-021-90458-2


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