Review
Copyright ©The Author(s) 2018. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Mar 21, 2018; 24(11): 1181-1195
Published online Mar 21, 2018. doi: 10.3748/wjg.v24.i11.1181
Functional macrophages and gastrointestinal disorders
Yue-Hong Liu, Yue Ding, Chen-Chen Gao, Li-Sheng Li, Yue-Xiu Wang, Jing-Dong Xu
Yue-Hong Liu, Yue Ding, School of Basic Medical Science, Beijing Capital Medical University, Beijing 100069, China
Chen-Chen Gao, Jing-Dong Xu, Department of Physiology and Pathophysiology, School of Basic Medical Science, Capital Medical University, Beijing 100069, China
Li-Sheng Li, Function Platform Center, School of Basic Medical Science, Capital Medical University, Beijing 100069, China
Yue-Xiu Wang, Beijing Institute for Brain Disorders, Capital Medical University, Beijing 100069, China
Author contributions: Liu YH and Ding Y contributed equally to the writing of this manuscript; Liu YH, Ding Y and Xu JD wrote the manuscript; Liu YH and Gao CC designed the illustrations; Li LS and Wang YX analyzed the data; Xu JD revised the manuscript.
Supported by National Natural Science Foundation of China, No. 81274173, No. 81673671 and No. 81270443; Beijing National Science Foundation, No. 7122017.
Conflict-of-interest statement: The authors do not have any relevant conflicts of interest (including relevant financial interests, activities, relationships and/or affiliations).
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Jing-Dong Xu, PhD, Assistant Professor, Department of Physiology and Pathophysiology, School of Basic Medical Science, Capital Medical University, No. 10, Xitoutiao, You An Menwai, Fengtai District, Beijing 100069, China. xujingdong@163.com
Telephone: +86-10-83911469 Fax: +86-10-83911469
Received: January 27, 2018
Peer-review started: January 28, 2018
First decision: February 10, 2018
Revised: February 12, 2018
Accepted: February 25, 2018
Article in press: February 25, 2018
Published online: March 21, 2018
Abstract

Macrophages (MΦ) differentiate from blood monocytes and participate in innate and adaptive immunity. Because of their abilities to recognize pathogens and activate bactericidal activities, MΦ are always discovered at the site of immune defense. MΦ in the intestine are unique, such that in the healthy intestine, they possess complex mechanisms to protect the gut from inflammation. In these complex mechanisms, they produce anti-inflammatory cytokines, such as interleukin-10 and transforming growth factor-β, and inhibit the inflammatory pathways mediated by Toll-like receptors. It has been demonstrated that resident MΦ play a crucial role in maintaining intestinal homeostasis, and they can be recognized by their unique markers. Nonetheless, in the inflamed intestine, the function of MΦ will change because of environmental variation, which may be one of the mechanisms of inflammatory bowel disease (IBD). We provide further explanation about these mechanisms in our review. In addition, we review recent discoveries that MΦ may be involved in the development of gastrointestinal tumors. We will highlight the possible therapeutic targets for the management of IBD and gastrointestinal tumors, and we also discuss why more details are needed to fully understand all other effects of intestinal MΦ.

Keywords: Macrophages, Homeostasis, Inflammatory bowel disease, Gastrointestinal tumors, Therapeutic targets

Core tip: The manuscript involves three components. First, after briefly describing the origin of macrophages (MΦ), it summarizes their general biologic features and common functions. The second component reveals the differences between resident MΦ in the intestine and those in other tissues. Notably, we depicted how resident MΦ participate in maintaining intestinal homeostasis and why they can maintain intestinal health by comparison between each of these distinct features. The third part discusses how the deficiency of this anti-inflammatory system leads to autoimmune diseases. However, we also discuss the many details of why intestinal MΦ and the underlying mechanism of inflammatory bowel disease and gut tumors remain obscure.