Epithelial cells: liaisons of immunity. (February 2020) - Larsen, Samantha B
Graphical abstract: Epithelial cells sense danger launching a relay to immune cells to restore homeostasis within barrier tissues. Epithelial cells raise alarm to immune cells, which arrive on scene to aid epithelial cells in reinforcing barrier integrity. Following the race to restore homeostasis, epithelial cells display enhanced performance when they sense future danger. Created with BioRender.com . Highlights: Epithelial cells sense their microenvironment via an arsenal of pattern recognition receptors that inform downstream responses. Microbial species tune epithelial-immune cell crosstalk to reinforce barrier integrity and/or mount host defense systems. If a barrier tissue is breached, epithelial cells release alarmins that signal to the immune system for support. After inflammation, epithelial cells retain chromatin accessibility at key immune loci that contribute to a heightened secondary response. Abstract : The surface and lining tissues of our body are exposed to the external environment, and as such these epithelial tissues must form structural barriers able to defend against microbes, environmental toxins, and mechanical stress. Their cells are equipped to detect a diverse array of surface perturbations, and then launch signaling relays to the immune system. The aim of these liaisons is to coordinate the requisite immune cell response needed to preserve and/or restore barrier integrity and defend the host. It has been recently appreciated that epithelial cells learn from these experiences. Following inflammatory exposure, long-lived stem cells within the tissue retain an epigenetic memory that endows them with heightened responsiveness to subsequent encounters with stress. Here, we review the recent literature on how epithelial cells sense signals from microbes, allergens, and injury at the tissue surface, and transmit this information to immune cells, while embedding a memory of the experience within their chromatin.