The activity of genes that help to control immune functions decreases when astronauts reach space, but this change reverses when they return to Earth, according to a new study.
A study funded by the Canadian Space Agency builds on research that suggests astronauts are more susceptible to infections while in space. Individuals on board the International Space Station (ISS) commonly suffer from skin rashes, as well as respiratory and non-respiratory diseases.
Lead author Dr Odette Laneuville, an associate professor at the Department of Biology of the University of Ottawa, said: “Here we show that the expression of many genes related to immune functions rapidly decreases when astronauts reach space, while the opposite happens when they return to Earth after six months aboard the ISS.”
The research team studied gene expression in leukocytes in 14 astronauts – three women and 11 men – who were on the ISS for between 4.5 and 6.5 months between 2015 and 2019.
They isolated leukocytes from 4ml of blood drawn from each astronaut at 10 time points: once pre-flight, four times in flight, and five times back on Earth.
They found 15,410 genes to be differentially expressed in leukocytes. Looking at patterns of changes in gene activity, they found two clusters, with 247 and 29 genes respectively, that changed their expression in tandem along the studied timeline.
Genes in the first cluster reduced when the astronauts were in space but increased again when they returned to Earth, while genes in the second cluster followed the opposite pattern.
Both clusters comprised mostly genes that code for proteins, but the predominant function in the first cluster was related to immunity, while those in the second cluster were related to cellular structures and functions.
Writing in Frontiers in Immunology, the authors say these results suggest that when someone travels to space, these changes in gene expression cause a rapid decrease in the strength of their immune system.
Professor Guy Trudel, from Department of Cellular and Molecular Medicine of the University of Ottawa, said: “A weaker immunity increases the risk of infectious diseases, limiting astronauts’ ability to perform their demanding missions in space. If an infection or an immune-related condition was to evolve to a severe state requiring medical care, astronauts while in space would have limited access to care, medication, or evacuation.”
Most genes in both clusters returned to their pre-flight level of expression within one year after return on Earth, and many did so within weeks.
However, this means that returning astronauts have a greater risk of infection for at least one month after landing back on Earth.
The authors suggest the change in gene expression of leukocytes under microgravity is triggered by ‘fluid shift’, where blood plasma is redistributed from the lower to the upper part of the body, including the lymphatic system.
This causes a reduction in plasma volume by between 10% and 15% within the first few days in space.
“The next question is how to apply our findings to guide the design of countermeasures that will prevent immune suppression while in space in particular for long duration flight,” said Dr Laneuville.
“The health of astronauts while in space, especially during long missions, would benefit from detecting both immune dysfunction and sub-clinical inflammation. Early detection provides opportunities for intervention, with the aim to prevent a progression towards severe symptoms.”
Source: Stratis D, Trudel G, Rochelau L, Pelchat M, and Laneuville O (2023) “The transcriptome response of astronaut leukocytes to long missions aboard the International Space Station reveals immune modulation.” Frontiers in Immunology, doi: 10.3389/fimmu.2023.1171103
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