As a kid, my father always emphasized the importance of sleep. Little did I know, as I hid under my blankets, reading a novel with a flashlight, that I was weakening my immune system.
The last few decades of research has revealed that sleep supports our immune systems, playing a crucial role in both innate and adaptive immunity. Our sleep-wake cycles are regulated by circadian oscillations, natural processes that are driven by exposure and response to light. Accumulating evidence suggests that many of our immune cells follow intrinsic clocks as well, where their activity, migration, and functions are regulated by core circadian genes. It has been shown that during sleep, serum levels of proinflammatory cytokines peaks, while numbers of immune cells flow and ebb. Sleep disturbances (due to interrupted sleep or altered sleep patterns) disrupts this clockwork, resulting in a shift in increased cytokine production during waking hours rather than during sleep. This shift is accompanied by a decreased antiviral responses, potentially conferring increased susceptibility to infectious disease. In fact, human studies have found that a lack of sleep is associated with higher risk of infections. Partial sleep deprivation is associated with reduced T cell frequencies and natural killer cell activity, both crucial cells in fighting against pathogens. Moreover, sleep was reported to affect T cell migration and improve T cell activity.
These changes in response to sleep deprivation are conserved across species, suggesting an important regulatory role of the circadian system in immunity. Although the mechanisms and evolutionary factors for this response are not yet fully understood, studies have shown that infecting mice at different times of the day results in different disease outcomes. This effect was attributed to the functions of macrophages, a specialized immune cell that is crucial in detection and defense against pathogens, which was regulated by a circadian clock gene. This temporal effect suggests that regulating our circadian rhythms may be beneficial in bolstering our immunity, particularly for those with higher risk of infections. In line with this, sleep deprivation can also affect response to certain vaccines, resulting in lower levels of antibody titers.
Not only does sleep affect immunity, but immune responses can also affect your quality of sleep. Higher levels of inflammation are correlated with changes in sleep duration and disrupted sleep patterns. Exposure of mice to influenza virus leads to changes in sleep architecture – decreases in rapid eye movement (REM) sleep – and longer sleep continuity. During infection, many proinflammatory cytokines are released, including interleukin (IL)1β. Administration of this cytokine directly into the cerebrospinal fluid of rabbits and rats was shown to increase the duration of nonREM sleep, otherwise known as deep sleep, impacting sleep pattern.
Understanding the crosstalk between circadian clock and our immune system will undoubtedly reveal insights into the mechanisms that govern these interactions and how regulation of sleep contributes to these systems. The next time you contemplate whether or not to go to bed, remember that curtailing sleep, unfortunately, does have long term consequences.
Ibarra-Coronado, Elizabeth G., Ana Ma. Pantaleón-Martínez,Javier Velazquéz-Moctezuma, Oscar Prospéro-García, Mónica Méndez-Díaz, Mayra Pérez-Tapia, Lenin Pavón, and Jorge Morales-Montor. 2015. “The Bidirectional Relationship between Sleep and Immunity against Infections.” Journal of Immunology Research 2015: 678164. https://doi.org/10.1155/2015/678164.
Irwin, Michael R. 2019. “Sleep and Inflammation: Partners in Sickness and in Health.” Nature Reviews Immunology19 (11): 702–15. https://doi.org/10.1038/s41577-019-0190-z.
Ray, David, and Gareth Kitchen. n.d. “Body Clock Affects How the Immune System Works –New Findings.” The Conversation. Accessed June 7, 2022. http://theconversation.com/body-clock-affects-how-the-immune-system-works-new-findings-129289.
“Sleep and Immune System.” 2019. Healthline. February 21, 2019. https://www.healthline.com/health-news/how-sleep-bolsters-your-immune-system