Scientists discovered during the early Apollo missions that microgravity in space disrupts human physiology and is harmful to astronauts’ health. Photo from NASA

Microgravity in space disrupts human physiology and is detrimental to astronaut health, a fact first recognized during the early Apollo missions when astronauts suffered inner ear disorders, cardiac arrhythmias, low blood pressure, dehydration, and calcium loss from their bones after their missions .

One of the most striking observations from Apollo missions was that just over half of the astronauts caught colds or other infections within a week of returning to Earth. Some astronauts have even seen dormant viruses like the chickenpox virus reactivate. This discovery stimulated studies of the effects of low gravity or “microgravity” on the immune system that scientists have been studying for decades with manned rocket launches, shuttle journeys and space station stays, or sometimes by simulating space gravity in terrestrial laboratories.

In the latest study, led by one of the earliest astronauts, Millie Hughes-Fulford, PhD, researchers from UC San Francisco and Stanford University have now shown that an astronaut’s immune system weakening while in space is likely due in part to an abnormal one Activation is due to immune cells called T regulator cells (Tregs).

Tregs are usually triggered to reduce the immune response when infection is no longer threatened and are important regulators of the immune response in diseases ranging from cancer to COVID-19. However, under microgravity conditions, the researchers found changes in Tregs that prepared them to go to work even before the immune system was challenged. When they stimulated an immune response in human immune cells from blood samples in weightlessness, using a chemical commonly used in research to mimic a pathogen, they found that Tregs helped suppress the immune response it triggered. This unexpected discovery will be published online in the journal on June 7th Scientific reports.

Millie Hughes-Fulford, PhD, spoke to Thomas Lang, PhD, in her lab at the San Francisco VA Medical Center in 2016. Photo by Noah Berger

Hughes-Fulford was the first female payload specialist to orbit the earth with her experiments in 1991, and for decades until her death from leukemia in Februaryshe examined the effects of weightlessness on health, initially with a focus on osteoporosis and later with a focus on the immune system. As a researcher at the San Francisco Veterans Affairs Medical Center Hughes-Fulford and a member of the UCSF faculty long associated with the medical school mentored aspiring space scientists, including the co-directors of this latest immunology study.

Jordan Spatz, PhD, a space scientist and medical student at UCSF who became a co-PI of the study after Hughes-Fulford’s death, noted that concerns about the health of space travelers are likely to increase as the commercialization and diffusion of space travel increases.

“At the beginning of the space program, most of the astronauts were young and extremely healthy, but now they have a lot more training and are older,” said Spatz. “Apart from the astronauts, with the commercialization of space travel, there will be many more older and less healthy people who experience weightlessness. From a space medicine perspective, we see that microgravity does many negative things to the human body, and we hope to mitigate some of the effects of microgravity during space travel. ”

The new study advanced previous research led by Hughes-Fulford, confirmed some of its earlier results from experiments in space and simulated weightlessness, while also contributing to additional molecular discoveries. Hughes-Fulford had previously noted weaker responses from T lymphocytes of the immune system, some of which attack specific pathogens directly and some of which help orchestrate the immune response.

“It’s a double punch,” said Co-PI Brice Gaudilliere, MD, PhD, associate professor in the anesthesia department at Stanford University School of Medicine. “There is a dampening of the immune activation reactions of the T lymphocytes, but also an aggravation of the immunosuppressive reactions caused by Tregs.” The researchers also found that “natural killer” lymphocytes were less active under simulated weightlessness, while antibody-producing B cells did not appear to be affected.

The researchers simulated weightlessness in blood samples with a special, cylindrical cell culture vessel with motorized rotation, a long-established tool in weightlessness research, but the method of single cell analysis was unique. Scientists identified individual immune cells by specific type and used metal tags and mass spectroscopy to simultaneously identify and quantify dozens of proteins that play a role in immune function, as well as confirming previously identified patterns of altered gene activation.

Financing: The study was funded by the UCSF Department of Biochemistry and Biophysics and the Stanford Department of Anesthesiology, Perioperative and Pain Medicine. No competing interests were declared.

The University of California, San Francisco (UCSF) is entirely focused on health sciences and is dedicated to advancing health worldwide through advanced biomedical research, graduate education in the life sciences and health professions, and excellence in patient care. UCSF health, which serves as the UCSF’s primary academic medical center Top specialist clinics and other clinical programs and has offices across the Bay Area.