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Astronaut study sheds light on what makes them get sick more easily in space

MARY LOUISE KELLY, HOST:

Astronauts must be in excellent health. They quarantine before blasting off. They live and work in a sterile environment. And yet, once in outer space, some have viral flare-ups or break out in rashes. A new study helps us understand why. Here's science reporter Ari Daniel.

ARI DANIEL, BYLINE: Molecular biologist Odette Laneuville wasn't expecting Jeremy Hansen, the Canadian astronaut, to accept her invitation to come over for dinner, but he did.

ODETTE LANEUVILLE: I was not ready. I just put a salad together. And I had some meat pie left from Christmas, so we just pulled some out and pretend I'm a good cook.

DANIEL: Nevertheless, dinner was a hit, and so were the conversations Laneuville had with Hansen that week at her lab at the University of Ottawa, where they discussed why some astronauts may be more vulnerable to infections in space.

LANEUVILLE: We are the host of multiple viruses and bacteria. And because we're healthy, we manage to keep those at check. But if we're stressed, or if there's a dysregulation of the immune system, then the virus will start being active - and likewise with bacteria.

DANIEL: ...Which can lead to infection - and Laneuville thought maybe something in space was triggering a change in the gene activity of the immune cells in astronaut blood that was allowing these opportunistic infections to surface. So she and her colleagues enlisted 14 American and Canadian astronauts, all headed to the International Space Station for several months at different times. Laneuville had their blood sampled before and after their missions here on Earth, but also during their time in outer space.

LANEUVILLE: You have to be very careful to secure everything. We don't want any leak - not a drop of blood. Otherwise, it will float in the air and contaminate everybody.

DANIEL: The astronauts spun the blood down and stored it in a super cold freezer until they returned to Earth.

LANEUVILLE: I was supposed to hire someone to process those, but then I said, no, they're too precious. This blood comes from space. It was my baby, and I had to take care of it.

DANIEL: Here's what that special blood revealed. Exactly 100 immune-related genes get dialed down in outer space, maybe due to stress. But maybe, Laneuville thinks...

LANEUVILLE: Those genes respond to a decrease in gravitational force.

DANIEL: That's right - genes that react to a change in gravity. Laneuville says that, when an astronaut enters microgravity, their blood shifts from their legs to their torsos and heads. It's uncomfortable, so their body reduces the fluid by up to 15%. But that now means that there are too many immune cells crammed into this smaller amount of blood. Laneuville thinks the drop in gene activity helps eliminate those extra cells.

LANEUVILLE: On top of that, it will affect the immune response mounting a line of defense against pathogen. It's as if the body is telling them, put your guards down.

DANIEL: ...Which would allow viral and bacterial infections normally held at bay to rise up, infecting the astronauts. But once they step foot on land again, the whole thing reverses. The genes get dialed back up, and plasma levels return to normal. This work is published in the journal Frontiers In Immunology.

JEREMY TEO: It's a good start.

DANIEL: Especially as we send astronauts farther and farther out, says Jeremy Teo, a biomedical engineer at NYU Abu Dhabi, who wasn't involved in the study - to the moon, to Mars...

TEO: As we go further, the feasibility of extraditing compromised astronauts back to Earth is just not there anymore. Hence, we need to develop new countermeasures.

DANIEL: Down the road, Teo says the study may also have something to say about those with compromised immune systems right here on Earth.

For NPR News, I'm Ari Daniel.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.

Ari Daniel is a reporter for NPR's Science desk where he covers global health and development.