CD163 and rheumatoid arthritis: In mouse tissues, recruitment of blood monocytes in response to ‘on-demand’ signal is often concomitant with a loss of tissue-resident macrophages due to emigration or death.80 In the synovium of active patients with RA, both S100A8/9+and CD163+macrophages are present, although the latter in much lower numbers.54 Similarly, in mouse models of arthritis, tissue-resident macrophages were present at the peak of inflammation, along with monocyte-derived macrophages, although outnumbered and with distinct transcriptomic profiles.