Tracking down immunodeficiency in astronauts

worthlessness is associated with health costs. (Image: Georgethefourth / iStock)

Unhealthy levitation: A stay in weightlessness weakens, among other things, the resistance of the astronauts to pathogens. A study is now providing new evidence of what is behind this effect. When the force of gravity is weak, the so-called regulatory T cells go crazy: They dampen the immune system to an unnatural level. The scientists hope that their results can contribute to the development of strategies to limit the health burdens of space travelers.

The release from the effect of gravity is fascinating – but it has long been known that hovering is not good for astronauts: the unnatural condition disrupts human physiology and can cause various health problems, such as cardiac arrhythmias, drop in blood pressure, dehydration and bone loss. An impairment of the immune system was already evident during the Apollo missions: more than half of the astronauts caught infections within a week of their return. Some even reactivated viruses that were dormant in the body.

Tests with simulated microgravity

What is the basis of the obvious weakening of the immune system has already been researched beforehand through studies during stays in space or in simulated weightlessness (microgravity) in earth-based laboratories. A research team led by Millie Hughes-Fulford from the University of California at San Francisco (UCSF) also looked at this topic. The scientist, who died at the age of 75 at the beginning of this year, took part in a manned space flight herself in 1991. In early studies, Hughes-Fulford and her team had already found evidence of a weakened T-lymphocyte response, some of which attack specific pathogens directly and others help orchestrate the immune response.

As part of the current study, the scientists have now examined the reactions of various representatives of human immune cells to weak gravity. A special device from microgravity research was used that, through motor-driven rotation, can expose cells in a culture vessel to altered effects of gravity. The immune cells, which were marked according to their type, were then examined individually using molecular biological and genetic methods in order to enable conclusions to be drawn about changes in their activity. They were compared with cells that were exposed to normal acceleration due to gravity.

A double blow is emerging

The researchers were initially able to confirm that the activity of T lymphocytes declines under unnaturally weak gravity conditions. But apparently this is only part of the problem: The analysis results suggest that the weakening of the astronauts’ immune system is also due to an abnormal activation of the regulatory T cells. These units, also known as suppressor T cells, are important masterminds in the body’s complex defense system: They prevent the development of autoimmune diseases through signal effects and “calm down” the body police after operations. Normally, the regulatory T cells become active in the body when there is no longer any threat of infection and the immune response can thus be shut down.

Under the conditions of microgravity, however, these cells already come into action before the immune system has been challenged, according to the results. In their investigations, the scientists also induced an experimental immune reaction in the cells in the containers. They found further evidence that the regulatory T cells suppress a normal immune response under unnaturally weak gravity conditions. “There is a double punch for the immune system,” says co-author Brice Gaudilliere of Stanford University. “Apparently, the activity of the T lymphocytes is attenuated and at the same time the immunosuppressive response by the regulatory T cells is intensified,” the scientist sums up.

The team now hopes that the results can help develop strategies to reduce the health burdens of space travelers. With the commercialization and intensification of manned space travel, this is becoming more and more important, say the researchers: “In the past, most astronauts were young and fit – but that has changed: there will now be increasingly older and less healthy people who are exposed to microgravity” says first author Jordan Spatz from UCSF. “With this in mind, we hope that it will be possible to mitigate some of the negative effects of this state of affairs during stays in space,” said Spatz.

Source: University of California in San Francisco, specialist article: Scientific Reports, doi: 10.1038 / s41598-021-90458-2

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