Circadian Clock Times Immune Response

The molecular response of an organism -- be it mouse or man -- to pathogenic invasion is controlled by circadian rhythms, researchers found.

In mice exposed to infection at the highest and lowest time of activity in the 24-hour light-dark cycle of an immune protein known as toll-like receptor 9 (TLR9), those whose exposure was at the nadir of TLR9 expression had much more severe sepsis, according to Erol Fikrig, MD, of Yale University, and colleagues.

Specifically, the animals exposed at 19:00 hours -- the highest activity period -- died sooner (at 31 hours versus 45 hours, P

"Nearly all organisms have developed mechanisms for anticipating environmental changes in order to optimize their survival," explained Fikrig and colleagues.

One such is circadian rhythm, which influences biological systems through neuroendocrine signaling according to the intensity of light.

Studies have increasingly shown that disruptions in daily routines, such as jet lag, can have a negative influence on immune function.

Moreover, certain diseases associated with altered immunity such as sepsis and rheumatoid arthritis display variations in symptom severity according to time of day, with the highest levels of inflammatory markers being seen during the night.

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