Abstract
Monocytes are subdivided into three subsets, which have different phenotypic and functional characteristics and different roles in inflammation and malignancy. When in man CD14 and CD16 monoclonal antibodies are used to define these subsets, then the distinction of non-classical CD14low and intermediate CD14high monocytes requires setting a gate in what is a gradually changing level of CD14 expression. In the search for an additional marker to better dissect the two subsets we have explored the marker 6-sulfo LacNAc (slan). Slan is a carbohydrate residue originally described to be expressed on the cell surface of a type of dendritic cell in human blood. We elaborate herein that the features of slan+ cells are congruent with the features of CD16+ non-classical monocytes and that slan is a candidate marker for definition of non-classical monocytes. The use of this marker may help in studying the role of non-classical monocytes in health and in diagnosis and monitoring of disease.
Highlights
The identification of monocytes in human blood has become much easier with advent of flow cytometry and the use of monoclonal antibodies to cell surface molecules
This antibody was generated by immunizing Balb/c mice with human blood mononuclear cells depleted of T and B cells and monocytes [4]
For lupus nephritis with pronounced sub-epithelial immune complex deposits an increased number of CD16+ cells had already been documented [65]. Consistent with these findings in a recent study on lupus nephritis an increase in the frequency of slan+ monocytes in class III and IV glomeruli was shown [66]. These slan data are obviously much more informative compared to staining for CD16+ cells because they strongly suggest the presence of nonclassical monocytes while the demonstration of CD16+ cells in tissue sections is less specific since this receptor is present on neutrophils and NK cells
Summary
The identification of monocytes in human blood has become much easier with advent of flow cytometry and the use of monoclonal antibodies to cell surface molecules. With the advent of transcriptome analysis, unsupervised hierarchical clustering approaches have demonstrated that the blood slan+ cells cluster with monocytes and not with dendritic cells [8, 9] These findings have provided additional strong evidence for the monocyte nature of the slan+ leukocytes. C-type lectin receptors CD368 (Dectin-3) and CLEC5A were found essentially absent both in CD16+ monocytes and in slan+ cells, while classical monocytes showed a strong expression of these markers [24]. Looking at these data, it is evident that the pattern of cell surface markers for the CD16+ monocytes and the slan+ cells is very similar. The congruent expression of these various functionally relevant receptors suggests similar functional properties of these cells
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