The loss of tolerance to CHI3L1 - A putative role in inflammatory bowel disease?

The incidence of inflammatory bowel disease (IBD) is steadily increasing. IBD is characterized by chronic inflammation of the gastrointestinal tract and is divided into the two main entities Crohn's disease (CD) and ulcerative colitis (UC). Genetic predispositions, environmental factors and a dysregulated immune response are known to be involved at the beginning of IBD. However, their etiopathogenesis is not yet fully understood. Over the last ten years, there has been increasing evidence of the involvement of the member of the 18-glycosylhydrolase family chitinase-3-like protein 1 (CHI3L1) in IBD. CHI3L1 is associated with various diseases such as cancer and chronic inflammatory diseases including rheumatoid arthritis or IBD as well as neurological diseases where it can act as a chemoattractant, mitogen or growth factor. This review will focus on the role of autoimmunity to CHI3L1 in IBD in the context of its expression in inflamed colonic epithelia and interaction with intestinal microbiota. Further, it will provide insights into the interaction of CHI3L1 with different mechanisms of the innate and adaptive immune response in IBD.