RNASeq profiles from two distinct F4/80+VCAM1+ sorted bone marrow populations are consistent with non-macrophage cells coated with macrophage fragments

The objective of this study was to characterise macrophage subsets in bone marrow (BM) isolated from Csf1r-EGFP mice. A concurrent imaging flow cytometry study conducted by our team unexpectedly revealed macrophage surface marker staining emanates from membrane-bound subcellular remnants associated with unrelated cells. Expression data from sorted BM “macrophage” populations was found to be consistent with macrophage fragments associated with non-macrophage cells. Granulocyte-specific genes were enriched within the CD11b+ “macrophage” (CD11b+F4/80+Ly6G-GFPloVCAM1+) populations, whereas CD11b- “macrophages” (CD11b-F4/80+GFP+VCAM1+) were consistent with a mixed cell population including both plasma cells and erythroblasts. This data demonstrates how fragmentation of hematopoietic tissue macrophages can result in misattribution of macrophage identity to non-macrophage populations, thereby undermining accuracy of macrophage ex vivo molecular profiles. mRNA profiles of two distinct sorted bone marrow cell populations (CD11b+ "macrophages" and CD11b- "macrophages") isolated from Csf1r-EGFP mice. Four biological replicates were analysed for each population.