Innate Lymphoid Cells in Mucosal Homeostasis, Infections, Autoimmune Disorders, and Tumors

Innate lymphoid cells (ILCs) are lymphocytes that lack specific antigen receptors. It has recently become apparent that ILCs comprise disparate subsets and that their diversity can be conceptualized using developmental and functional modules similar to those that designate CD4 T helper cells. ILC1 produce interferon-γ, ILC2 secrete interleukin (IL)-5 and IL-13, and ILC3 produce IL-22 and/or IL-17. ILCs preferentially localize close to the epithelial barriers at the interface between the environment and the associated lymphoid tissues. Upon pathogen invasion, ILCs detect cytokines produced by epithelial cells and antigen-presenting cells and respond by producing cytokines that preserve barrier integrity. Conversely, inappropriate or sustained activation of ILCs can lead to excessive inflammation and tissue damage. In this review, we highlight recent progress in the characterization of ILCs in the oral and gastrointestinal mucosa and their contributions to homeostasis, defense against infections, inflammatory bowel disease, and tumors.