Standardized Flow Cytometry Assay for Identification of Human Monocytic Heterogeneity and LRP1 Expression in Monocyte Subpopulations: Decreased Expression of This Receptor in Nonclassical Monocytes

Abstract

In this article, we present a flow cytometry assay by which human blood monocyte sub-populations—classical (CD1411CD162), intermediate (CD1411CD161), and non-classical (CD141CD1611) monocytes—can be determined. Monocytic cells wereselected from CD451leukocyte subsets by differential staining of the low-density lipo-protein receptor-related protein 1 (LRP1), which allows reducing the spill-over of natu-ral killer cells and granulocytes into the CD161monocyte gate. Percentages ofmonocyte subpopulations established by this procedure were significantly comparablewith those obtained by a well-standardized flow cytometry assay based on the HLA-DRmonocyte-gating strategy. We also demonstrated that LRP1 is differentially expressed atcell surface of monocyte subpopulations, being significantly lower in nonclassicalmonocytes than in classical and intermediate monocytes. Cell surface expression ofLRP1 accounts for only 20% of the total cellular content in each monocyte subpopula-tion. Finally, we established the within-individual biological variation (bCV%) of cir-culating monocyte subpopulations in healthy donors, obtaining values of 21%, 20%,and 17% for nonclassical, intermediate, and classical monocytes, respectively. Similarvalues of bCV% for LRP1 measured in each monocyte subpopulation were alsoobtained, suggesting that its variability is mainly influenced by the intrinsic biologicalvariation of circulating monocytes. Thus, we conclude that LRP1 can be used as a thirdpan-monocytic marker together with CD14 and CD16 to properly identify monocytesubpopulations. The combined determination of monocyte subpopulations and LRP1monocytic expression may be relevant for clinical studies of inflammatory processes,with special interest in atherosclerosis and cardiovascular disease.VC2014 InternationalSociety for Advancement of Cytometry