People often feel tired when they get sick, and researchers think that the cytokines helping fight infection may induce sleepiness. If immune-system activation can affect sleep, might the converse be true—do sleep cycles affect the immune system? Erol Fikrig and colleagues at the Yale University School of Medicine isolated some of the molecular players in both the circadian and the innate immune systems. They showed that the strength of some immune responses was indeed affected by the time of day.
First, they looked at mice lacking a functional Per2 gene, which helps control the master circadian clock in the brain. Without a working copy, the mouse’s clock was altered, along with the expression of the Toll-like receptor 9 (TLR9), which is part of the innate immune response and detects the presence of bacterial or viral DNA in the cytoplasm of infected cells. Co-first authors Adam Silver and Alvaro Arjona tracked ...
