Decoded: Why do you sleep when you're sick?

New York: Researchers, including one from India, have discovered a gene that acts as a direct link between disease and the need for more sleep. In a study of more than 12,000 fruit fly lines, researchers at the University of Pennsylvania in the United States discovered the unique gene called nemuri, which increases sleep requirements.

The nemuri protein fights germs through its intrinsic antimicrobial activity. It is secreted by brain cells to allow deep and prolonged sleep after infection. "While it is common for sleep and healing to be closely related, our study establishes a direct link between sleep and the immune system and provides a possible explanation for the increase in sleep during illness", said Amita Sehgal, a professor at the university.

Without the nemuri gene, flies were more easily awakened during daily sleep and their urgent need for more sleep – induced by sleep deprivation or infection – was reduced. On the other hand, sleep deprivation, which increases the need for sleep and, to a certain extent, the infection, prompted the nemuri to express itself in a small group of nested fly neurons near a known structure promoting sleep in the brain.

Overexpression of nemuri resulted in increased sleep in bacteria-infected flies and increased survival compared to uninfected control flies. In response to infection, the nemuri appears to kill microbes, most likely in the peripheral parts of the fruit fly body, and increases sleep through its action on the brain.

In addition, the researchers, in the study published in the journal Science, noted that an immune cell molecule – interleukin-1 (IL-1) – is implicated in human sleep. IL-1 accumulates after prolonged sleep and seems to promote sleep, suggesting that nemuri is an effective link between immune function and sleep.