Altering gene expression in white blood cells, space travel compromises the immune system

Increasing evidence suggests that astronauts are more susceptible to infections during space travel. Skin rashes, respiratory and non-respiratory diseases are common among astronauts aboard the International Space Station (ISS). Additionally, astronauts tend to shed a higher number of live virus particles, including Epstein-Barr virus, varicella-zoster, herpes-simplex-1, and cytomegalovirus. These observations raise questions about the impact of space travel on the immune system and the factors contributing to this immune deficit.

A recent study published in Frontiers in Immunology, led by Dr. Odette Laneuville, an associate professor at the Department of Biology of the University of Ottawa, sheds light on the subject. The study, funded by the Canadian Space Agency, examined gene expression in white blood cells (leukocytes) of 14 astronauts (including three women and 11 men) who spent 4.5 to 6.5 months aboard the ISS between 2015 and 2019. Blood samples were collected at various time points, including pre-flight, during the mission, and after returning to Earth.

The analysis revealed differential expression of 15,410 genes in leukocytes. Among these genes, two distinct clusters of 247 and 29 genes respectively exhibited consistent patterns of expression throughout the study period. The genes in the first cluster showed decreased expression during space travel and an increase upon return to Earth, while the genes in the second cluster displayed the opposite pattern. The genes in the first cluster predominantly functioned in relation to immunity, whereas those in the second cluster were associated with cellular structures and functions.

These findings indicate that space travel induces rapid changes in gene expression, leading to a weakened immune system. A compromised immune system puts astronauts at a higher risk of infectious diseases, which can significantly impact their ability to carry out missions in space. Limited access to medical care, medication, and evacuation in space further exacerbate this risk.

Fortunately, the study also revealed that most genes returned to their pre-flight expression levels within one year after returning to Earth, typically much sooner. However, the full restoration of immune resistance to its pre-flight strength remains uncertain, with factors such as age, sex, genetic variations, and childhood exposure to pathogens potentially influencing the duration of this recovery period.

The researchers hypothesize that the altered gene expression in leukocytes during microgravity is triggered by "fluid shift." This phenomenon involves the redistribution of blood plasma from the lower to the upper body, including the lymphatic system, resulting in a 10% to 15% reduction in plasma volume within the initial days of space travel. Fluid shift is known to induce significant physiological adaptations, including changes in gene expression.

Moving forward, the study emphasizes the importance of utilizing these findings to develop countermeasures that can prevent immune suppression during long-duration space flights. Dr. Laneuville highlights the need for further research to inform the design of effective prophylactic measures against immune deficits in space.