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Going to space may weaken your immune system against fungal infections, according to a new study.

New research reveals that fruit flies raised in space have weaker immune systems than their Earth-raised counterparts.

Lead researcher Deborah Kimbrell of University of California Davis College of Biological Sciences found that Drosophila flies raised on the Space Shuttle show weakened immunity to fungus.

Researchers explained that the flies were sent into space as eggs on a 12-day mission aboard the Space Shuttle Discovery. The flies then take about 10 days to develop into adults. After the flies were brought back to earth, researchers tested their responses to two different infections: a fungus, which flies combat through a pathway mediated by the Toll receptor, and a bacterial infection that flies fight off through a gene called imd ("Immune deficiency").

Scientists said that the findings could apply to humans because both the Toll and Imd pathways have counterparts in humans and other mammals.

Researchers found that the Toll pathway was "non-functional" in space-raised flies. However, the response through the Imd pathway was robust.

Previous studies also found that when flies' resistance to fungus was improved when they were tested in centrifuge under hypergravity conditions.  Researchers also found that the resistance was the same at normal and hypergravity for the mutant yuri gagarin, which lacks normal responses to gravitational fields. These findings suggest that there is a link between gravity ad immune response.

Kimbrell and her team have two theories as to how microgravity affects the immune system. The first theory involves heat-shock proteins, which are produced in response to physiological stress. Flies raised in space showed high expression of genes heat-shock proteins, which bind directly with mammalian Toll receptors. Researchers believe that the high level of heat-shock proteins may also moderate Toll activation in fruit flies. The second theory as that microgravity disrupts the behavior of proteins outside the cell -- an area that is more essential for Toll than for imd signaling.

The findings are published in the journal PLOS ONE.