While space travel may not be for the weak hearted, the bold move may have repercussions, as a new study reveals.

According to researchers at the University of California, Davis, weightlessness in space could weaken the immunity system in Drosophila flies.

The study, funded by NASA, was published on Friday, January 24, in the journal PLOS ONE and reveals how growing up on a space shuttle has weakened a pivotal aspect of the immune system in the Drosophila flies. The study focuses on the genetic make-up that enables the flies to guard against infections and has raised questions that could the same be applicable for human space travelers as well?

The adverse effect of spaceflights on immune responses is an established fact. Deborah Kimbrell, lead researcher from the University of California, Davis, and her colleagues from the Department of Molecular and Cellular Biology used Drosophila flies to observe the connection between gravity and immunity. Drosophila flies were used as their immune system is quite similar to that of mammals such as humans and mice.

The flies were sent into space on a 12-day mission as eggs on the space shuttle Discovery. The flies took approximately 10 days to become adults and grew up in orbit. Post their return to Earth, Kimbrell and her team of researchers tested the flies' responses to two different infections - a fungus and a bacterial infection. The fungus is mediated by a Toll receptor, whereas the bacterial infection is resisted by flies via the Imd gene. Interestingly, both these have corresponding parts in humans, as well as other mammals, and play an important role in fighting off infections.

The team of researchers discovered that in the space-raised flies, the Imd pathway continued to work while the Toll receptor was "non-functional." They found that these Drosophila flies were more susceptible to fungal infections.

Further Earth-based experiments reinforced the role of gravity in weakening immune systems. The researchers tested normal flies in a centrifuge under hypergravity and discovered that these had more resistance to fungal infections when compared to their space-grown counterparts.

Kimbrell opines that future space shuttles that are designed for long missions should include centrifuges that crew could deploy to maintain their bone and muscle mass, which in turn may benefit their immune system.