The immune system alters mammalian circadian clock gene expression, perhaps explaining why fatigue accompanies some infections and autoimmune diseases, according to a study in this week's Proceedings of the National Academy of Sciences. The authors found that a protein involved in mammalian immunity interferes with circadian clock gene expression and promotes sleep in mice."The study certainly provides a framework within which to address the question of how immunomodulators affect both the timing and the quantity or quality of sleep," said Mark Opp of the University of Michigan in Ann Arbor, who was not involved in the study.The immune response to microbial infection activates pro-inflammatory molecules such as tumor necrosis factor alpha (TNF-α). Previous work has suggested that TNF-α causes lethargy and fatigue in people with cancer, rheumatoid arthritis, and sleep apnea. Animal studies have also shown that TNF-α enhances sleep, but the mechanism has remained...

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