Two Distinct Subsets Are Identified from the Peritoneal Myeloid Mononuclear Cells Expressing both CD11c and CD115

To this date, the criteria to distinguish peritoneal macrophages and dendritic cells (DCs) are not clear. Here we delineate the subsets of myeloid mononuclear cells in the mouse peritoneal cavity. Considering phenotypical, functional, and ontogenic features, peritoneal myeloid mononuclear cells are divided into 5 subsets: large peritoneal macrophages (LPMs), small peritoneal macrophages (SPMs), DCs, and 2 MHCII CD11c CD115 subpopulations (i.e., MHCII CD11c CD115 CD14 CD206 and MHCII CD11c CD115 CD14 CD206 ). Among them, 2 subsets of competent Ag presenting cells are demonstrated with distinct functional characteristics, one being DCs and the other being MHCII CD11c CD115 CD14 CD206 cells. DCs are able to promote fully activated T cells and superior in expanding cytokine producing inflammatory T cells, whereas MHCII CD11c CD115 CD14 CD206 cells generate partially activated T cells and possess a greater ability to induce Treg under TGF-β and retinoic acid conditions. While the development of DCs and MHCII CD11c CD115 CD14 CD206 cells are responsive to the treatment of FLT3 ligand and GM-CSF, the number of LPMs, SPMs, and MHCII CD11c CD115 CD14 CD206 cells are only influenced by the injection of GM-CSF. In addition, the analysis of gene expression profiles among MHCII peritoneal myeloid mononuclear cells reveals that MHCII CD11c CD115 CD14 CD206 cells share high similarity with SPMs, whereas MHCII CD11c CD115 CD14 CD206 cells are related to peritoneal DC2s. Collectively, our study identifies 2 distinct subpopulations of MHCII CD11c CD115 cells, 1) MHCII CD11c CD115 CD14 CD206 cells closely related to peritoneal DC2s and 2) MHCII CD11c CD115 CD14 CD206 cells to SPMs.