Fungal Dysbiosis in Inflammatory Bowel Disease - Where Are We?

Since there is growing evidence supporting the role of dysbiosis in the pathogenesis of inflammatory bowel disease (IBD), intensive researsch has focused on identifying key players among bacterial components. However, available data on the role of fungal microbiota in IBD pathogenesis is scarce. We review important microbiome studies focusing on fungal dysbiosis in patients with IBD and describe mechanisms of intestinal microbiota dysfunction resulting from both clinical and experimental studies. We focus on recent results of fungal microbiota research from observational studies to interventional studies regarding immune-mediated interactions between fungal microbiota and intestinal inflammatory status. In IBD, bacterial microbiota diversity is reduced, while fungal biodiversity is reduced only in ulcerative colitis (UC) and not during Crohn's disease (CD). Fungal depletion in experimental models has proved to worsen acute colitis. As for identifying the fungal influence upon inflammatory response, several species among Saccharomyces genera exert regulatory effect on dendritic cells, modulating various anti-inflammatory cytokine production. In clinical observational studies, specific associations between bacterial and fungal components were identified, both during flares and remission periods, involving different changes for UC and CD, but specific mechanisms between fungal components and host immune system are still under debate. Conclusions Interkingdom microbiome alterations are found in IBD, which suggest that fungi may also be involved in disease pathogenesis, with different involment in UC and CD. Fungal dysbiosis is a certain player in IBD, both through composition and biodiversity alteration and further studies are needed to specify the fungi-host immune interactions.