Regulation of ILC3/Th17-Mediated Intestinal Immune Response by Circadian Rhythm

The circadian rhythm is a widely-recognized phenomenon, according to which the life activities of organisms change periodically, synchronizing with the day and night cycles. The activities of the immune system are also regulated by the circadian rhythm. Group 3 innate lymphoid cells (ILC3s) and T helper 17 (Th17) cells (ILC3/Th17) are the innate and adaptive subsets of immune cells mediating type 17 immune response, which is featured by the expression of transcription factor retinoid orphan receptor gamma t (RORγt) and the production of interleukin (IL)-17 and IL-22. The processes of type 17 immune response are completed mainly through the participation of ILC3/Th17 and are closely associated with the intestinal immune response. Recent studies have found that the immune response mediated by ILC3/Th17 is intricately regulated by the circadian rhythm through molecular mechanisms controlling the circadian rhythm, or through other external factors that change according to the light-darkness cycle, for example the food intake rhythm. The secretion of cytokines changes along with the regulatory effect of circadian rhythm on ILC3/Th17, which in turn impacts, to a certain degree, on the onset and development of intestinal inflammatory diseases, including bacterial infection and autoimmune diseases. The understanding of mechanisms regulating ILC3/Th17 responses by the circadian rhythm may promote better understanding of the course of action of the immune system and facilitate the development and discovery of potential targets for treatment of intestinal inflammatory diseases.