Th17 Cells in Inflammatory Bowel Disease: An Update for the Clinician.

Abstract

INTRODUCTION Inflammatory bowel disease (IBD), including Crohn’s disease (CD) and ulcerative colitis (UC), are chronic systemic relapsing-remitting conditions that are thought to be the end result of dysregulated host immune responses to enteric flora.1 The pathogenesis of IBD is complex. Genome-wide association studies (GWAS) and animal models implicate multiple mechanisms of disease induction and propagation.2 Indeed, every component of the gut from the enteric microbiome to (host) epithelial and immune cells including antigen presenting cells (APCs) such as dendritic cells and macrophages and T and B cells have all been linked to the pathogenesis of IBD.2 In this regard, it has become clear over the last 20 years that the IL-17 producing subset of CD4+ T-cells, termed “Th17” cells, are strongly implicated in the pathogenesis of IBD.2–5 This connection has in turn focused intense attention on Th17 cells, leading to IBD therapies targeting these pathways.6, 7 Herein, we review the role of Th17 cells in the pathogenesis and treatment of IBD, with a focus on clinically relevant avenues including emerging therapies. Our goal is to make this subject accessible while encompassing the most relevant aspects of Th17 biology. This review is written with the clinician in mind and is aimed at providing an overview of Th17 cell biology in humans. Much has been written about the fundamental biology of Th17 cells in mice and humans, and we refer the reader interested in the unadulterated complexity of the subject to any number of outstanding reviews.8–10