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.

该生物钟将生理过程和行为与环境光周期耦合。这种耦合可确保将耗能巨大的过程与一天中生物体最活跃的时间同步，从而提高整体适应性。宿主免疫是一个精力密集的过程，需要多种免疫细胞类型的协调才能感应，交流和响应多种微生物。有趣的是，生物钟携带着免疫细胞的发育，功能以及向环境光周期的运输。这种夹带导致宿主在昼夜周期中对微生物病原体的敏感性变化。另外，生物钟与微生物群进行双向通讯，驻留在动物上皮表面附近的微生物。这种双向交换在调节宿主免疫力中起着至关重要的作用，对于生物节律的代谢控制也是至关重要的。在这里，我们回顾了生物钟在指导宿主免疫程序中的作用，并考虑了共生和致病微生物如何影响生物钟的生理过程。