Sleep and the circadian system significantly influence immune functions. Studies show that immune parameters like naive T cells and pro-inflammatory cytokines peak during early nocturnal sleep, while immune cells with immediate effector functions and anti-inflammatory cytokines peak during daytime wakefulness. Although sleep and circadian rhythms are intertwined, comparisons of nocturnal sleep with 24-hour wakefulness suggest that sleep enhances T cell extravasation and redistribution to lymph nodes. Sleep also selectively enhances cytokines that promote antigen-presenting cell (APC) and T helper cell interactions, such as interleukin-12. Sleep after vaccination increases antigen-specific T cells and antibody titres, indicating a role in immunological memory formation. This role is associated with slow wave sleep (SWS) and a pro-inflammatory endocrine milieu characterized by high growth hormone and prolactin levels and low cortisol and catecholamine concentrations. Neuroimmune interactions are based on shared signals like hormones, neurotransmitters, cytokines, and chemokines. Immune cells traffic to various body sites and can reach the brain. Lymphatic tissues are innervated by sympathetic and peptidergic nerves. The endocrine and autonomous nervous systems regulate immune functions through hormones, neural innervation, blood flow, and substrate supply. These systems are interconnected, with hormones, neurotransmitters, cytokines, and chemokines often overlapping in function. The immune system includes leukocytes, which can be categorized by their ontogenetic development, hematopoietic lineage, maturation site, primary action site, antigen specificity, function, and cytokine profile. These cells serve immune defense by detecting and eliminating foreign antigens, altered self-antigens, and cells indicating damage. The adaptive immune response involves antigen uptake by APC, migration to lymph nodes, antigen presentation to T helper cells, activation and differentiation of T cells, and the formation of immunological memory. The sleep-wake cycle is a key manifestation of the circadian rhythm, with sleep and the circadian system tightly intertwined. Immune parameters like leukocyte numbers, function, proliferation, and cytokine production exhibit diurnal rhythms, with peaks during the rest period and active period. The early rest period is characterized by a pro-inflammatory state, with increased levels of growth hormone, prolactin, and melatonin, and decreased cortisol and catecholamines. Pro-inflammatory cytokines and Th1 cytokines peak during the rest period, while anti-inflammatory activity is prevalent during wakefulness. Sleep enhances the consolidation of immunological memory, which is crucial for effective adaptive immune responses. The sleep-wake cycle and circadian system work together to regulate immune functions, with sleep playing a key role in immune activation and memory formation. Sleep also supports the redistribution of immune cells to lymph nodes and enhances the production of pro-inflammatory cytokines like IL-12. However, prolonged sleep loss can have detrimental effects on immune functions, highlighting the importance of adequate sleep for generalSleep and the circadian system significantly influence immune functions. Studies show that immune parameters like naive T cells and pro-inflammatory cytokines peak during early nocturnal sleep, while immune cells with immediate effector functions and anti-inflammatory cytokines peak during daytime wakefulness. Although sleep and circadian rhythms are intertwined, comparisons of nocturnal sleep with 24-hour wakefulness suggest that sleep enhances T cell extravasation and redistribution to lymph nodes. Sleep also selectively enhances cytokines that promote antigen-presenting cell (APC) and T helper cell interactions, such as interleukin-12. Sleep after vaccination increases antigen-specific T cells and antibody titres, indicating a role in immunological memory formation. This role is associated with slow wave sleep (SWS) and a pro-inflammatory endocrine milieu characterized by high growth hormone and prolactin levels and low cortisol and catecholamine concentrations. Neuroimmune interactions are based on shared signals like hormones, neurotransmitters, cytokines, and chemokines. Immune cells traffic to various body sites and can reach the brain. Lymphatic tissues are innervated by sympathetic and peptidergic nerves. The endocrine and autonomous nervous systems regulate immune functions through hormones, neural innervation, blood flow, and substrate supply. These systems are interconnected, with hormones, neurotransmitters, cytokines, and chemokines often overlapping in function. The immune system includes leukocytes, which can be categorized by their ontogenetic development, hematopoietic lineage, maturation site, primary action site, antigen specificity, function, and cytokine profile. These cells serve immune defense by detecting and eliminating foreign antigens, altered self-antigens, and cells indicating damage. The adaptive immune response involves antigen uptake by APC, migration to lymph nodes, antigen presentation to T helper cells, activation and differentiation of T cells, and the formation of immunological memory. The sleep-wake cycle is a key manifestation of the circadian rhythm, with sleep and the circadian system tightly intertwined. Immune parameters like leukocyte numbers, function, proliferation, and cytokine production exhibit diurnal rhythms, with peaks during the rest period and active period. The early rest period is characterized by a pro-inflammatory state, with increased levels of growth hormone, prolactin, and melatonin, and decreased cortisol and catecholamines. Pro-inflammatory cytokines and Th1 cytokines peak during the rest period, while anti-inflammatory activity is prevalent during wakefulness. Sleep enhances the consolidation of immunological memory, which is crucial for effective adaptive immune responses. The sleep-wake cycle and circadian system work together to regulate immune functions, with sleep playing a key role in immune activation and memory formation. Sleep also supports the redistribution of immune cells to lymph nodes and enhances the production of pro-inflammatory cytokines like IL-12. However, prolonged sleep loss can have detrimental effects on immune functions, highlighting the importance of adequate sleep for general