When the Body Clock Runs Down, the Immune System Takes Time Off

The circadian clock is a finely tuned genetic mechanism that regulates our sleep cycle and key metabolic changes during the 24-hour cycle. It also may help determine whether we get sick or not, according to a new Yale School of Medicine study published online Feb 16 in the journal Immunity.

"People intuitively know that when their sleep patterns are disturbed, they are more likely to get sick," said Erol Fikrig, professor of epidemiology and microbial pathogenesis, and senior author of the study. "It does appear that disruptions of the circadian clock influence our susceptibility to pathogens."

Yale University researchers show that in mice the circadian clock controls the level of activity of a key immune system gene that responds to the presence of bacteria and viruses. When expression levels of the Toll-like receptor 9 (TLR-9) gene were highest, the immune system response to vaccination was greatest, the study found. In addition, mice were best able to withstand infections when TLR-9 levels were highest, the researchers discovered.

The findings suggest that jet lag may directly contribute to illnesses when traveling and that there might be better times of day to get vaccinated.

"Sleep patterns of patients in intensive care are often disrupted because of the noise and prolonged exposure to artificial light," says Fikrig, who is also an investigator for the Howard Hughes Medical Institute. "It will be important to investigate how these factors influence immune system response."