Role of flagellin in Crohnʼs disease: Emblematic of the progress and enigmas in understanding inflammatory bowel disease

Elevated immune responses to the enteric microbiota have long been associated with inflammatory bowel disease (IBD), especially Crohn's disease. In recent years there has been considerable progress in identifying a number of the specific bacterial and host molecules whose interactions mediate these responses. However, deciphering the role of these interactions in the pathophysiology of IBD remains a difficult challenge, in part due to the very complex nature of the epithelial cell / microbial / immune cell interactions that play a central role in maintaining the gut's well-being. This article reviews such progress and discusses these challenges in the context of focusing on 1 particular protein, bacterial flagellin.