Validation of CSF-1 receptor (CD115) staining for analysis of murine monocytes by flow cytometry.

CD115, the receptor for colony stimulating factor 1 (CSF-1), is essential for survival and differentiation of monocytes and macrophages and is therefore frequently used to define monocyte subsets and their progenitors in immunological assays. However, CD115 surface expression and detection by flow cytometry is greatly influenced by cell isolation and processing methods, organ source and disease context. In a systematic analysis of murine monocytes we define experimental conditions that preserve or limit CD115 surface expression and staining by flow cytometry. We also find that, independent of conditions, CD115 surface levels are consistently lower in Ly6Clo monocytes than in Ly6Chi monocytes, with the exception of Ly6Clo monocytes in the bone marrow. Furthermore, in contrast to IL-34, the presence of CSF-1 impairs CD115 antibody-staining in a dose-dependent manner, which, in a model of ischemic kidney injury with elevated levels of CSF-1, influenced quantification of kidney monocytes. Thus, staining and experimental conditions affect quantitative and qualitative analysis of monocytes and may influence experimental conclusions.