pathogens Review Trichuris muris Model: Role in Understanding Intestinal Immune Response, Inflammation and Host Defense Yeganeh Yousefi 1,2 , Sabah Haq 1,2 , Suhrid Banskota 1,2 , Yun Han Kwon 1,2 and Waliul I. Khan 1,2, *   Citation: Yousefi, Y.; Haq, S.; Banskota, S.; Kwon, Y.H.; Khan, W.I. Trichuris muris Model: Role in Understanding Intestinal Immune Response, Inflammation and Host Defense. Pathogens 2021, 10, 925. https://doi.org/10.3390/ pathogens10080925 Academic Editor: Luis I. Terrazas Received: 5 July 2021 Accepted: 20 July 2021 Published: 22 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Farncombe Family Digestive Health Research Institute, McMaster University Health Sciences Centre Room 3N7, 1280 Main St. W, Hamilton, ON L8N 3Z5, Canada; yeganeh.yousefi.90@gmail.com (Y.Y.); haqs4@mcmaster.ca (S.H.); banskots@mcmaster.ca (S.B.); yyoon90@gmail.com (Y.H.K.) 2 Department of Pathology and Molecular Medicine, McMaster University, 1200 Main St. W, Hamilton, ON L8N 3Z5, Canada * Correspondence: khanwal@mcmaster.ca; Tel.: +1-905-521-2100 (ext. 22846) Abstract: Several parasites have evolved to survive in the human intestinal tract and over 1 billion people around the world, specifically in developing countries, are infected with enteric helminths. Trichuris trichiura is one of the world’s most common intestinal parasites that causes human parasitic infections. Trichuris muris, as an immunologically well-defined mouse model of T. trichiura, is extensively used to study different aspects of the innate and adaptive components of the immune system. Studies on T. muris model offer insights into understanding host immunity, since this parasite generates two distinct immune responses in resistant and susceptible strains of mouse. Apart from the immune cells, T. muris infection also influences various components of the intestinal tract, especially the gut microbiota, mucus layer, epithelial cells and smooth muscle cells. Here, we reviewed the different immune responses generated by innate and adaptive immune components during acute and chronic T. muris infections. Furthermore, we discussed the importance of studying T. muris model in understanding host–parasite interaction in the context of alteration in the host’s microbiota, intestinal barrier, inflammation, and host defense, and in parasite infection-mediated modulation of other immune and inflammatory diseases. Keywords: intestinal helminth; Trichuris muris; immune response; host–parasite interaction; host defense; epithelial cells; goblet cells; enteroendocrine cells; smooth muscle cells 1. Introduction Intestinal parasites are one of the most important parasites in terms of their widespread prevalence, and they have major socioeconomic impacts on both developing and developed countries by affecting human and animal well-being, productivity, and agriculture. Among the intestinal parasites, intestinal helminth infections are the most prevalent parasites, and they occur through contact with parasite eggs and larvae. It is estimated that about 2 billion people worldwide are infected with helminths [1]. Trichuris trichiura is a soil-transmitted helminth, and recent estimates suggest that there are approximately 465 million people worldwide with T. trichiura infection [2–4]. Infection with T. trichiura is associated with adverse health consequences in humans, with the majority being children [5,6]. T. muris, a murine pathogen, shares extensive homology at genomic, transcriptomic and morphological levels to T. trichiura and is extensively used as a laboratory mouse model for T. trichiura [7]. T. muris, with its unique advantage of producing heteroge- neous immunological outcomes in different mouse strains, is a widely used model for understanding host–parasite interactions. Models of helminth infection are of immense importance in exploring the pathology and pathophysiology of many gastrointestinal disorders [8]. Due to well-defined immunity and biology, the T. muris model is widely Pathogens 2021, 10, 925. https://doi.org/10.3390/pathogens10080925 https://www.mdpi.com/journal/pathogens