In contrast, while a few isolated cells with a neutrophilic morphology were seen to be positive for ACKR2 staining in healthy controls (supplementary Fig. S2A, available at Rheumatology Online), the majority of ACKR2-positive cells in the RA patients lacked this morphology (supplementary Fig. S2B, available at Rheumatology Online) suggesting little involvement of neutrophils in contributing to the elevated ACKR2 expression. This evidence concerns the gene ACKR2 and rheumatoid arthritis.