WASHINGTON, Jan. 24 (Xinhua) -- Drosophila flies that grew up in space had a weakened immune system after returning to Earth, U. S. researchers said Friday.
It's well-established that spaceflight affects immune responses. Lead researcher Deborah Kimbrell from the University of California, Davis, and her colleagues from the Department of Molecular and Cellular Biology in the UC Davis College of Biological Sciences, used Drosophila to study the relationship between immunity and gravity because Drosophila share many fundamentals of the immune system with mammals such as mice and humans.
The flies, which take about 10 days to develop into adults, were sent into space as eggs on a 12-day mission aboard the Space Shuttle Discovery.
After they returned to Earth, the researchers tested their responses to two different infections: a fungus, which flies fight off through a pathway mediated by the Toll receptor, and a bacterial infection that flies resist through a gene called Imd. Both the Toll and Imd pathways have counterparts in humans and other mammals.
While the response through the Imd pathway was robust, the Toll pathway was "non-functional" in space-raised flies, Kimbrell said.
In Earth-based experiments, the researchers found that when flies were tested in a centrifuge under hypergravity, or increased gravity, conditions, their resistance to the fungus was improved, suggesting that their Toll pathway was boosted.
Future spacecraft designed for long missions, said Kimbrell, should include centrifuges that crew could use to keep up bone and muscle mass, as this might also have a beneficial effect on astronauts' immune systems.
The findings were published in the U.S. journal PLOS ONE.