Scary threats to human health dominate the news these days. Space travel may help scientists strengthen our bodies' ability to fight such threats. Two upcoming studies on leukocytes-human defense cells-seek to understand how these tiny warriors mount their defense.

Astronauts' immune systems don't work as well in microgravity as on Earth. Knowing why is key to protecting astronauts' health and could lead to new treatments on Earth for those with impaired immune systems.

TripleLux-B launches to the International Space Station in December 2014 on SpaceX's fifth commercial resupply mission. In February 2015, TripleLux-A will follow aboard SpaceX's sixth mission. Both investigations examine cellular changes in the immune system and separate out the specific effects of microgravity from other spaceflight factors like radiation.

In human immune systems, large white blood cells called leukocytes are the first line of defense against infection. These cells engulf foreign bodies and produce a burst of reactive oxygen that helps destroy invaders.

TripleLux-A will test leukocytes in rats on the space station. TripleLux-B will explore how microgravity causes changes in cellular-level genetic mechanisms, including DNA repair. It will compare microgravity-induced changes in rat leukocytes with similar immune system cells in blue mussels.

These mussel and rat cells are considered model organisms; they have characteristics making them easy to maintain, reproduce and study in a laboratory. The mussels, for example, generate large numbers of immune system cells that are easy to collect without harming the animal.

"Our goal with TripleLux-B is to find out whether the cells of the immune system of the mussel, which is older in an evolutionary sense, are affected in the same way as those in the immune system of an astronaut-or, in this case, a rat," says Principal Investigator Peter-Diedrich Hansen, Ph.D., professor of toxicology and senior research scientist at Germany's Berlin Institute for Technology. "And if not, what makes it different?"

The experiments will use a safe substitute for bacteria called zymosan, which is produced from yeast cells. Researchers will use a luminescent chemical called Luminol to detect oxygen bursts occurring after the tiny warriors devour the invaders.

Previous studies showed gravity changes affect immune system cells. Experiments during parabolic flights and in centrifuges demonstrated rapid and reversible alterations to the immune system process.

However, these studies are limited because microgravity conditions either were short-lived or artificially created. Conducting experiments on the space station provides prolonged exposure to microgravity and an opportunity to observe the leukocytes' oxygen-burst reactions.

"Gravitational conditions on Earth could have been one of the requirements for development of the machinery of the oxidative burst reaction," says TripleLux-A Principle Investigator Oliver Ullrich, professor of anatomy and space biotechnology in Switzerland and Germany.

"A major challenge is finding out if our cellular machinery is able to work without gravitational force or if our cellular architecture will keep us dependent on Earth's gravity." This research could help scientists develop ways to manage or prevent microgravity-induced changes in immune system function or, simply put, make these tiny warriors space-ready.

To clarify whether microgravity, radiation or a combination is responsible for immune system changes during spaceflight, researchers will expose the cells to microgravity and simulated Earth gravity. The latter will be created in the European Space Agency's BIOLAB centrifuge.

Data from these conditions will be compared with measurements of accumulated radiation doses from a reference experiment on the ground. Researchers will assess whether microgravity and radiation work together to create a stronger effect. This investigation must be performed aboard the space station because cosmic radiation cannot be simulated on Earth.

A measurement device developed for these experiments could potentially be adapted into a tool for monitoring astronauts' immune systems during long-duration spaceflights. The investigations also are an opportunity to test this device.

These experiments on how space affects the immune system may help us better employ its tiny warriors to keep us healthy no matter what invaders attack.