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 MHCIICD11cCD115 subpopulations (i.e., MHCIICD11cCD115CD14CD206 and MHCIICD11cCD115CD14CD206). Among them, 2 subsets of competent Ag presenting cells are demonstrated with distinct functional characteristics, one being DCs and the other being MHCIICD11cCD115CD14CD206 cells. DCs are able to promote fully activated T cells and superior in expanding cytokine producing inflammatory T cells, whereas MHCIICD11cCD115CD14CD206 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 MHCIICD11cCD115CD14CD206 cells are responsive to the treatment of FLT3 ligand and GM-CSF, the number of LPMs, SPMs, and MHCIICD11cCD115CD14CD206 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 MHCIICD11cCD115CD14CD206 cells share high similarity with SPMs, whereas MHCIICD11cCD115CD14CD206 cells are related to peritoneal DC2s. Collectively, our study identifies 2 distinct subpopulations of MHCIICD11cCD115 cells, 1) MHCIICD11cCD115CD14CD206 cells closely related to peritoneal DC2s and 2) MHCIICD11cCD115CD14CD206 cells to SPMs.