[Sleep and immune system]

Sleep is a process that occupies one third part of the life of the human being, and it is essential in order for the individual to be able to maintain body homeostasis. It emerges as an important regulator of the immune system since, during sleep, the necessary functions to maintain its balance are carried out. On the other hand, decreased sleep has deleterious effects that alter the metabolism and produce an increase in the secretion of C-reactive protein, interleukin (IL)-6 and tumor necrosis factor (TNF). These cytokines activate NF-κB; therefore, sleep disturbance can be a risk factor for the development of chronic inflammatory and metabolic diseases. Pro-inflammatory cytokines IL-1, IL-6 and TNF increase non-rapid eye movement sleep, whereas anti-inflammatory cytokines such as IL-4 and IL-10 decrease it. Sleep can modify the immune system function by inducing changes in the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system. In turn, the circadian rhythm of hormones such as cortisol and adrenaline, which have a nocturnal decrease, favors different activities of the immune system. The purpose of the present review is to address different aspects of sleep and their relationship with the immune system.