Human Monocyte Heterogeneity as Revealed by High-Dimensional Mass Cytometry

Objective— Three distinct human monocyte subsets have been identified based on the surface marker expression of CD14 and CD16. We hypothesized that monocytes were likely more heterogeneous in composition. Approach and Results— We used the high dimensionality of mass cytometry together with the FlowSOM clustering algorithm to accurately identify and define monocyte subsets in blood of healthy human subjects and those with coronary artery disease (CAD). To study the behavior and functionality of the newly defined monocyte subsets, we performed RNA sequencing, transwell migration, and efferocytosis assays. Here, we identify 8 human monocyte subsets based on their surface marker phenotype. We found that 3 of these subsets fall within the CD16+ nonclassical monocyte population and 4 subsets belong to the CD14+ classical monocytes, illustrating significant monocyte heterogeneity in humans. As nonclassical monocytes are important in modulating atherosclerosis in mice, we studied the functions of our 3 newly iden...