New Insight into Intestinal Mast Cells Revealed by Single-Cell RNA Sequencing.

Mast cells (MCs) are tissue-resident immune cells distributed in all tissues and strategically located close to blood and lymphatic vessels and nerves. Thanks to the expression of a wide array of receptors, MCs act as tissue sentinels, able to detect the presence of bacteria and parasites and to respond to different environmental stimuli. MCs originate from bone marrow (BM) progenitors that enter the circulation and mature in peripheral organs under the influence of microenvironment factors, thus differentiating into heterogeneous tissue-specific subsets. Even though MC activation has been traditionally linked to IgE-mediated allergic reactions, a role for these cells in other pathological conditions including tumor progression has recently emerged. However, several aspects of MC biology remain to be clarified. The advent of single-cell RNA sequencing platforms has provided the opportunity to understand MCs' origin and differentiation as well as their phenotype and functions within different tissues, including the gut. This review recapitulates how single-cell transcriptomic studies provided insight into MC development as well as into the functional role of intestinal MC subsets in health and disease.