Space travel risks: How does the immune system react to zero gravity?

More than in any previous year, 2023 has seen a rising number of "space tourists". Besides the effects of zero gravitiy, does space impact our immune system?

This article was translated from the original German version.

The immunological limits of human adaptation to space

Under the direction of the Swedish Karolinska Institute, researchers investigated the influence of weightlessness on the T-cells of the human immune system. Previously, a decrease in this cell group had been repeatedly observed in astronauts after a stay in space. This effect on the human immune system makes space a rather hostile environment for humans. The changes to the immune system make astronauts more susceptible to infections and can lead to the reactivation of latent viruses.

The acquired immunodeficiency persisted in the astronauts even after their return to Earth. More than half of the Apollo crew developed bacterial or viral infections after landing on Earth. The space environment appears to have a profound effect on adaptive immunity. This is also indicated by advances in space research on mice and humans. The long-term goal is therefore to find ways to make manned missions to space safer. To achieve this, however, the underlying pathomechanism must first be understood.5

What does the space environment actually do to a living organism?

The organism has to learn to cope with exposure to microgravity, increased radiation, psychological stress and isolation in an artificial environment. This is not without consequences: In mice, a decrease in the volume of the thymus was observed during spaceflight. Scientific study data allow us to rule out the apoptosis of CD4+CD8+ T cells as the cause of the decrease in T cells during spaceflight. Murine transcriptome analyses have shown that there is a down-regulation of genes associated with the activation and proliferation of T cells. It has also been shown that microgravity has a negative influence on T cell activation.5

Consequences of long-term microgravity exposure for the immune system

The research group used blood samples from eight healthy volunteers to investigate the effects of microgravity on the immune system. The healthy volunteers were exposed to dry immersion for a total of 21 days. The blood samples were taken 7 days before dry immersion, on days 7, 14 and 21 during dry immersion and 7 days after dry immersion. The 21-day dry immersion was considered a long-term microgravity exposure.

The research group was able to demonstrate the long-term effects of microgravity on T cell gene expression programmes. T cells exposed to microgravity changed their transcription programme quite rapidly. This was due to a down-regulation of protein-coding and non-coding genes that were responsible for controlling the activation and differentiation of T cells. At the same time, there was an upregulation of genes that are crucial for naive T cells.5

The study concludes: immune systems get weaker in space

Weightlessness led to an increase in the proportion of naive T cells. At the same time, the differentiation of T cells was reduced. This may be associated with a longer activation phase of naive T cells after contact with an intruder. This slows down the fight against infections. This may also explain the reduced effectiveness against tumour cells. Based on these study results, methods can now be developed to reverse these changes in the genetic programme of the immune cells.5

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  5. Gallardo-Dodd CJ. et al. (2023). Exposure of volunteers to microgravity by dry immersion bed over 21 days results in gene expression changes and adaptation of T cells. Sci Adv. 2023 Aug 25;9(34):eadg1610.