CD163 and rheumatoid arthritis: Although classification of M1 and M2 macrophage subsets in humans is not as clear as in mice3, both subsets can be identified in inflamed synovia of RA patients8, 9, 10, 11, using haemoglobin scavenger receptor CD163 as the main marker for human M2 macrophages, both in vitro and in situ2, 12.