Interactions among microbes, the immune system, and the circadian clock
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REVIEW
Interactions among microbes, the immune system, and the circadian clock John F. Brooks II 1 & Lora V. Hooper 1,2 Received: 9 June 2020 / Accepted: 25 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The circadian clock couples physiological processes and behaviors to environmental light cycles. This coupling ensures the synchronization of energetically expensive processes to the time of day at which an organism is most active, thus improving overall fitness. Host immunity is an energetically intensive process that requires the coordination of multiple immune cell types to sense, communicate, and respond to a variety of microorganisms. Interestingly the circadian clock entrains immune cell development, function, and trafficking to environmental light cycles. This entrainment results in the variation of host susceptibility to microbial pathogens across the day-night cycle. In addition, the circadian clock engages in bi-directional communication with the microbiota, resident microorganisms that reside in proximity to the epithelial surfaces of animals. This bi-directional interchange plays an essential role in regulating host immunity and is also pivotal for the circadian control of metabolism. Here, we review the role of the circadian clock in directing host immune programs and consider how commensal and pathogenic microbes impact circadian physiological processes. Keywords Circadian rhythms . Circadian clock . Immunity . Pathogens . Microbiota
Day-night light cycles and their impact on biology Every 24 hours, the Earth rotates once around its axis. This rotation results in a day-night cycle that is experienced by virtually all life on Earth, from cyanobacteria to humans [1, 2]. These rhythms in natural light entrain rhythmic behaviors such as eating and sleeping, and thus, many aspects of animal behavior and physiology are in synchrony with this daily environmental change. Most animals feed during the awake, or “active,” phase, which occurs during the day if they are diurnal and at night if they are nocturnal. Feeding is This article is a contribution to the special issue on: Neuro-immune Interactions - Guest Editor: David Farrar * John F. Brooks, II [email protected] * Lora V. Hooper [email protected] 1
Department of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
2
The Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
counterbalanced by a distinct fasting phase that occurs while sleeping, or during the “inactive” phase. These rhythmic changes in behavior are tied to rhythmic changes in the environment, such as food availability, possibility of predator encounter, and as we will discuss in this article, the possibility of exposure to infectious microorganisms. Most organisms have the ability to anticipate daily rhythmic changes in their environment, which allows coordination of energy-intensive metabolic activities with nutrient availability. They do s
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