Abstract

The coevolution of a mutualistic relationship between the host and the microbiota required specialized adaptations of the mucosal immune system to tolerate the intestinal bacteria and contain them in the lumen while remaining responsive to pathogen colonization and invasion. Nevertheless commensal microorganisms are not ignored and can signal to epithelial cells and interact with immune cells in the mucosa to influence the activity of the immune system. The host innate and adaptive immune responses also regulate the structure and composition of the intestinal microbiota, leading to a homeostatic balance. This Lecture will highlight recent advances in our understanding of this complex interplay and specific microorganisms that perform functions important for host physiology and homeostasis. The disruption of this balance is marked by dysbiosis and disturbances in the mucosal immune system and barrier function, which could have pathogenic outcomes. I will present examples of the role of microbiota in inflammatory diseases and therapeutic potential of ‘cornerstone’ species or microbial consortia to prevent or treat diseases.