LAUSR

The gut contains the largest macrophage pool in the body, with populations of macrophages residing in the mucosa and muscularis propria of the gastrointestinal (GI) tract. Muscularis macrophages, which are located within the muscularis propria, interact with cells essential for GI function, such as interstitial cells of Cajal (ICC)1-4, enteric neurons (ENs)5, smooth muscle cells (SMCs)6, enteric glia7 and fibroblasts like cells8, suggesting these immune cells contribute to several aspects of GI function. This review focuses on the latest insights on the factors contributing to muscularis macrophage heterogeneity and the functional interaction of muscularis macrophages with other cell types essential for GI function. This review integrates the latest findings on macrophages in other organs with growing knowledge of MM to better understand their role in a healthy and diseased gut. We will first describe the factors that contribute to MMs heterogeneity, and secondly, we will describe the nature of MM interaction with cells regulating GI function. Finally, we will also describe the growing evidence suggesting a critical role of another immune cell type, the mast cell, in the GI normal and diseased physiology.