Published online Mar 21, 2018. doi: 10.3748/wjg.v24.i11.1181
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
Processing time: 48 Days and 6.4 Hours
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.
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.