Daily light cycles help to set animals' response to infection.

Lora Hooper of the University of Texas Southwestern Medical Center in Dallas and her colleagues showed that a protein that controls whether certain white blood cells mature is in turn controlled by proteins that set daily rhythms. When mice were exposed to abnormal light cycles, rhythm-setting proteins sent signals to the immune system, prompting it to make more inflammatory cells in the gut.

Inflammation protected the mice against bacterial infection, but it also made them more susceptible to inflammatory bowel disease and colitis. The findings might explain why shift workers and others with disrupted sleep cycles are more prone to immune disorders.

Science 342, 727–730 (2013)