Introduction Human Monocytes
Monocytes in humans are being studied extensively due to the ease of access, while information on their precursors in bone marrow is more limited. The preferred approach, when analyzing these cells, is to avoid unnecessary processing, since monocytes are extremely sensitive and any purification step can alter their phenotype and function. Therefore, work with whole blood is recommended whenever possible.
For identification in flow cytometry antibodies CD14, CD16, anti-HLA-DR are recommended at minimum, but precision can be improved by using additional antibodies for exclusion of contaminant cells like NK cells and non-leukocytes.
Novel approaches like mass cytometry and single cell sequencing provide a high number of parameters per cell. These data are subjected to uniform manifold approximation and projection (UMAP) processing for definition and visualization of cell clusters. Here the established monocyte subsets, i.e. classical, intermediate and non-classical, are detected but often additional clusters emerge. These need to be consolidated by functional and clinical data and it needs to be determined whether these clusters represent novel cell types or transient cell states.