"The atypical chemokine receptor 1 (ACKR1) was discovered on erythrocytes as the Duffy blood group antigen ( Cutbush et al., 1950 ), also called Duffy-antigen/receptor for chemokines, or DARC ( Novitzky-Basso and Rot, 2012 ). Erythrocytes are terminally differentiated anuclear cells with no transcription and limited translation. Accordingly, within the erythroid lineage ACKR1 expression occurs first and is the highest in erythroblasts ( Duchene et al., 2017 ). Additionally, ACKR1 expression characterizes venular endothelial cells (ECs) ( Pruenster et al., 2009 ; Thiriot et al., 2017 ), including those lining bone marrow (BM) sinusoids ( Duchene et al., 2017 ). This well-established, distinctive pattern of cell expression has been directly challenged by a publication purporting ACKR1 expression in mouse BM by macrophages, but not erythroblasts and ECs, suggesting that macrophage ACKR1 engages its non-cognate ligand CD82 on hematopoietic stem cells (HSCs) to maintain their quiescence ( Hur et al., 2016 ). In light of the extensive literature, these findings have been particularly provocative, as this was the first description of ACKR1 expression by any leukocyte type and, if correct, would change current concepts of ACKR1 involvement in pathophysiology. The reported ACKR1 expression by macrophages in Hur et al. relied on using commercial anti-ACKR1 antibody FAB6695, which has neither been validated by the manufacturer nor by the authors. This prompted us to investigate the specificity of FAB6695 and scrutinize the apparent ACKR1 expression in BM macrophages"