Impact of sleep on innate immune cells

Recent studies have shown that sleep has a strong impact on different components of the immune system. Sleep deprivation has been described to affect both humoral as well as cellular immunity. Previously, the NLR ligand muramyldipeptide (MDP), chemically unique cell wall component of all bacteria, has been identified as a sleep-promoting factor in humans and animals, which accumulates during the active period to eventually induce slow wave sleep (SWS). On the other hand, sleep deprivation leads to a lethal sepsis in rats. Here we addressed whether sleep has an impact on the cellular components in blood and spleen and on the outcome of infection. Our results show that sleep deprivation (SD) in mice for up to 6 h led to a significant reduction of cell numbers in the blood in particular of monocytes whereas no effect was seen for PMNs. Further, we observed a reduction of monocytes in the spleen. After intravenous infection of mice with the model pathogen Yersinia enterocolitica, to mimic sepsis, the bacterial load in the spleen of SD-mice was significantly higher one and three days post infection. Also the survival of the SD-Mice was significantly reduced compared to the control group. These data suggest that sleep regulates homeostasis and function of innate immune cells, which are important in the early defence against pathogens.