Mucosal immune systems of pediatric inflammatory bowel disease: A review

Inflammatory bowel disease (IBD) is characterized by chronic inflammation of the gastrointestinal tract in chronic or recurrent remission phase and is classified as Crohn's disease (CD) and ulcerative colitis (UC). IBD is a multifactorial disease that results from genetic and environmental factors, immunological disorders, and gut microbiota dysregulation called dysbiosis. Recently, the number of patients with IBD in Japan has been increasing. This review describes studies of T cells, such as type 1 helper T (Th1) and type 1 cytotoxic T (Tc1) cells, and cytokines, such as IL-17 and IL-21, as representatives of mucosal immunity in IBD. Th1 cells and Tc1 cells are involved in Peyer's patches of CD. IL-12 significantly reduced the production of IL-17 but significantly increased in that of IFN-γ, and IL-21 reduced IL-17 production. It also describes genetic analysis studies on the cause of very early-onset IBD (VEO-IBD). Furthermore, 11.6% of patients with VEO-IBD presented with monogenic IBD in Japan. Genetic analysis for patients with VEO-IBD and suspected monogenic IBD was investigated. XIAP and heterozygous SLCO2A1 were detected owing to the result of functional confirmation, and several candidate genes were detected. Cytokine analysis and genetic analysis studies have revealed several pathophysiologies of IBD. Clinical and basic studies on mucosal immunity as well as immunological and genetic analyses are currently ongoing and are anticipated to provide an elaborate understanding of the pathophysiology of IBD.