Immunology, Medical News, World health

Scientists find underlying mechanism behind why space travel weakens our immune system

Microgravity in space disrupts human physiology and is harmful to astronaut health, as indicated with astronauts who have experienced inner ear abnormalities, heart arrhythmia, hypotension, dehydration, and loss of calcium from their bones after their missions.

One of the most interesting findings from the Apollo missions was that slightly over half of the astronauts were ill with colds or other diseases within a week after landing. Even dormant viruses, such as the chickenpox virus, had been reactivated in many of these astronauts.

These findings sparked interest in the scientific community, particularly regarding the effects of weak gravity, or “microgravity,” on the immune system, which scientists have now been investigating for decades through manned rocket launches, shuttle missions, and stints on the International Space Station, as well as by simulating space gravity in earthbound labs.

Researchers 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), according to a recent study led by Millie Hughes-Fulford, PhD, one of the first female astronauts.

Tregs are critical regulators of immune responses in illnesses ranging from cancer to COVID-19, and are generally prompted to ramp down immune responses when infection is no longer a concern. The researchers discovered modifications in Tregs in microgravity that readied them to go to work even before the immune system was challenged.

When scientists utilized a substance often used in studies to imitate a disease pathogen to induce an immune response in human immune cells from blood samples in microgravity, they discovered that Tregs helped dampen the immunological response that was induced. This unexpected finding was reported in the journal Nature Scientific Reports on June 7th.

Hughes-Fulford became the first female payload specialist to orbit Earth with her experiments in 1991, and she investigated the effects of microgravity on health for decades, initially with an emphasis on osteoporosis and then with a focus on the immune system, until her death due to leukemia in February. Hughes-Fulford trained aspiring space scientists, including the co-principal investigators of this new immunology study, as a researcher at the San Francisco Veterans Affairs Medical Center and a UCSF faculty member long affiliated with the Department of Medicine.

After Hughes-Fulford’s death, the study’s co-PI, Jordan Spatz, PhD, a space scientist and UCSF medical student, pointed out that as space flight becomes more commercialized and popular, worries about space passengers’ health are expected to rise.

“Early in the space program, most astronauts were young and extremely healthy, but now they tend to have much more training and are older,” Spatz said. “In addition, apart from astronauts, with the commercialization of space flight there will be many more older and less healthy individuals experiencing microgravity. From a 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.”

The new study builds on Hughes-Fulford’s earlier work, confirming some of her past findings from space and simulated microgravity trials while also bringing fresh molecular discoveries. Hughes-Fulford had previously discovered that immune system T cells, some of which fight certain pathogens directly and others of which assist and regulate the immune response, had lower responses.

“It’s a double whammy,” said co-PI Brice Gaudilliere, MD, PhD, an associate professor in the Department of Anesthesia at Stanford University School of Medicine. “There is a dampening of T lymphocyte immune activation responses, but also an exacerbation of immunosuppressive responses by Tregs.” The researchers also found that under simulated microgravity, “natural killer” lymphocytes were shown to be less active, whereas antibody-producing B cells appeared to be unaffected.

The researchers used a customized, cylindrical, cell-culture tank with motor-driven rotation to replicate microgravity in blood samples, which is a well-established microgravity research instrument, but the method of single-cell analysis was novel. The researchers employed metal tags and mass spectrometry to simultaneously identify and quantify hundreds of proteins involved in immune function, as well as corroborate previously known patterns of altered gene activity.

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