Cell Wars

Immune cells vs. invaders: it's a war going on in every healthy human body. When the combatants travel to space, say NASA scientists, curious things happen...

When you wake up, maybe you yawn, switch off your alarm clock, and listen for the perking of an automatic coffee maker -- a normal morning routine on Earth.

But if you were in orbit, the first thing you'd do is take a little roll of cotton, swish it around in your mouth, and then drop it in a tube filled with preservative. The cotton collects viruses, and the goal of that good-morning ritual is to help determine why astronaut saliva contains more viruses in space than it does on the ground.

It's not a trivial question.

Our bodies are chock-full of tiny invaders: bacteria, viruses, protozoans. Multitudes inhabit our gut, more slip in on the food we eat and through the air we breathe. Usually they're not a problem. Indeed, some are even helpful -- and the ones that aren't are kept in check by our vigorous immune system, which marks and destroys pathogens before they get out of control. Without immune systems, humans would die.

In space, our immune system functions differently. This complex system consists, essentially, of disease-fighting cells that can travel throughout the body. There are many kinds of immune cells; two of the most important are B-cells, which send out antibodies -- proteins that latch onto germs or other problem-causing invaders, flagging them as invaders to be destroyed, and T-cells, which are the soldiers of the system, physically attacking and destroying pathogens.

In space, these cells don't work the way they do on the ground. T-cells, for example, don't multiply properly; there aren't as many of them as there should be. They can't move well. They don't signal each other as effectively. Overall, they seem less able to destroy invading germs.

Here on Earth, doctors have learned that stress can suppress the immune system by causing the body to release hormones that affect the way T-cells behave. Likewise, the unique physical and psychological stresses of space flight (takeoff and landing, for example) might trigger immune-altering hormones. Another possibility is that something about space itself -- weightlessness, perhaps, and not hormones at all -- might affect immune cells directly.