In 2006, NASA launched 75 fruit flies on STS-121 for 13 days; Discovery returned with about 3,000, including a new generation that developed in space

NASA's experiments with fruit flies in zero gravity unveiled significant weaknesses in their immune systems. Observations indicated these flies produced fewer specialized immune cells and exhibited a diminished ability to combat bacteria. Further investigations demonstrated that their responses to fungal infections were also altered in space. These discoveries illuminate potential immune function disruptions among model organisms during spaceflight, raising important concerns for upcoming long-duration human space missions.