ESA astronaut Thomas Reiter was the first European on a long-duration mission to the International Space Station. In 2006 he spent over five months in space for the Astrolab mission. One of the experiments for Astrolab was Leukin, an experiment to study how human immune system cells adapt to weightlessness. A batch of human immune cells was allowed to float in microgravity while another was held in a centrifuge to simulate gravity. In this video Thomas is adding a chemical to the immune cells to make them think they are under attack. The process is performed in a portable glovebox for safety reasons. Nothing can escape the box and contaminate the International Space Station. The cells are then injected with a fixative to create a snapshot of the cells activity. The cells were stored in ESA’s Minus Eighty-Degree Laboratory Freezer for analysis back on Earth where researchers have discovered that living in space weakens astronauts’ immune systems. By comparing the samples, researchers saw what was stopping the immune cells from working. A specific transmitter in the immune cells stops working in weightlessness. The findings are providing clues on how to tackle diseases on Earth before symptoms appear.