While the barrier-like regulatory phenotype of lining layer MerTKposTREM2posVSIG4pos macrophages in healthy joints and RA in remission is well characterized, the phenotype of macrophages in the diseased hyperplastic lining layer, which serves as the niche for the recently described iDC3-driven activation of CCL5-producing memory T-cells in RA2, remains poorly understood. This evidence concerns the gene CCL5 and rheumatoid arthritis.