With a new crew arriving at the International Space Station, astronauts will be relieved to know that they won’t have to worry about a major aspect of their immune system being compromised. While researchers know a lot about astronauts’ skeletal and muscular health during spaceflight and when they return to Earth, much less is known about how spaceflight affects immunity. It has been generally thought, until now, that spaceflight has a detrimental impact on all aspects of the immune system.