Studies have shown that germline Il22−/− and Il22Ra1−/− mice are more susceptible to chemical- and pathogen-induced colitis.4,10–14 However, because IL-22Ra1 is expressed by various intestinal epithelial cells (IECs) such as secretory, absorptive, and intestinal stem cells (ISCs),15 it is unclear how IL-22 provides mucosal protection and what the specific role is of each cell type. Here, IL22RA1 is linked to colitis.