According to a study from NPJ Microgravity, long stays on board the ISS noticeably changed the way cosmonauts' and astronauts' immune systems work in conditions of weightlessness, the effects of which may put their lives at risk during long-term missions.
In recent years, doctors have actively studied the effects of a long stays in space on the human body. Most of these studies were carried out onboard American "shuttles", aboard the ISS and observing some Russian "biosatellites". Scientists have now been able to uncover a number of threats to human health, especially for future Martian colonists and deep space explorers.
The study reveals experiments on the fruit fly Drosophila, which showed that long exposure to weightlessness leads to a weakening of the innate immunity, and which made those insects vulnerable to fungi, as well as certain genetic changes. Moreover, according to the study life in space accelerates the aging of the bone marrow inside which the new immune cells form.
Brian Crucian and his colleagues from The Lyndon B. Johnson Space Center (USA), further revealed a manifestation of the effects of weightlessness on the immune system. They traced how the immune system of two dozen astronauts and cosmonauts reacted to a six-month stay onboard the ISS. The scientists explain, that during these trips, the ISS crew made self-examinations by taking blood and tissue samples and freezing them for the return to the Earth. After the "Union" and the "shuttles" landing, Crucian and his colleagues analyzed these samples and compared them with those taken before mission's launch. As it turned out, a long journey in weightlessness leads to significant rearrangements of the immune system, by suppressing the work of a number of immune cells. As a result, the strength of the immune response was reduced even after the crews return, and the ability of their bodies to fight infections was also reduced.
These results confirmed longstanding suspicions of scientists, that life in space leads to serious consequences for the immune system's functioning. Brian Crucian explains, that all previous medical researches were conducted among astronauts who participated only in the short space flights. For this reason, doctors could not say with 100% certainty, what was the source for the immune system reduction - a stress, takeoff and landing or the weightlessness. Older studies, such as the one conducted during the Soviet Salyut-6 long-duration orbital space station, back in 1977, concluded that space flight negatively impacts the human immune response, but the reasons for the reduced response remain unclear.
Now some scientists seem certain that the absence of gravity significantly affects our immune system operation, making the human body more vulnerable. This weakness is not only critical for fighting "external enemies" like a bacteria, viruses and fungi, but by the "internal" culprits of disease like Herpes labialis and some autoimmune diseases.
Scientists still are not sure about the reasons behind immune system weakening, but they do recommend to refrain from organizing the long-term missions to Mars and other planets, where the crews will not be able to seek professional medical help. Scott Kelly and his Russian counterpart, Mikhail Kornienko blasted off earlier this year for a 1 year mission in space ab oard the ISS. Kelly will be the first American to spend a continuous year in space; Russian Valeri Polyakov spent over a year aboard the Mir space station back in the 1990s. It will be interesting to see who these space explorers cope with the long stent in weightlessness. During their year on the ISS, Kelly and Kornienko are slated to perform daily cognitive, visual, and even microbial and metabolic tests.