Astroimmunology Series | Part 1: How does outer space affect our immune system?

I first heard about this when my PhD colleague presented it as part of her mini-proposal- a lab meeting segment where we could pitch and defend cool new experiments to try.

I was hooked immediately.

Immune cells form a protective shield against deadly infections. So when astronauts travel to space, their immune system needs to be ready to tackle infections (or space bugs). Turns out, they have more to deal with than just bugs.

Any cell taken farther from Earth would experience a combination of stressors: reduced gravity (or microgravity), cosmic radiation, and temperature fluctuations. Each of these stressors damages something fundamental - the structural support or cytoskeleton.

The cytoskeleton is the protein scaffolding that gives cells their structure. But it does a lot more than just provide shape. It controls cell division, positions receptors where they need to detect bugs and threats, and enables immune cells to migrate to sites of damage.

In microgravity, this scaffolding becomes disorganized. Microtubules, responsible for cell division, become disrupted. F-actin networks, necessary for cell movement, depolymerize. The optimal trafficking of receptors that sense threats is disturbed. Even brief exposure to microgravity alters epigenetic markers and chromatin structure.

The downstream consequences of this structural reorganization lead to weakened immune responses. Immune cells divide more slowly than normal. They detect fewer bugs. They migrate to problematic areas less efficiently. Altered gene expression levels change protein production, which can further impair immune function.

Galactic cosmic rays damage DNA and result in the overproduction of free radicals. Space radiation also affects mitochondria (the cell's energy source), impairing ATP production.

Space suits and shuttles shield astronauts from some of these effects. However, immune cells still experience significant stress. They overexpress heat shock proteins (HSPs) - an emergency repair system that helps repair misfolded proteins under stress conditions.

Beyond these direct environmental impacts, spaceflight also affects immune cells indirectly. For example, astronauts experience elevated cortisol levels due to mission-related stress, which suppresses T-cell development. Disrupted circadian rhythms further compromise immune surveillance, creating a perfect storm for immune dysfunction.

This is the first post in my new series on Astroimmunology - The emerging field studying how spaceflight reshapes our immune system.

References

1.          Winer, D. A. et al. Astroimmunology: the effects of spaceflight and its associated stressors on the immune system. Nat. Rev. Immunol. 26, 189–212 (2026).