Other ABC‐like cells, such as CD21−/low B cells and CD20+T‐bet+CD11c+ B cells, are also found in autoimmune patients [5, 6, 7], and are enriched in the synovial fluid (SF) of patients with active RA [8, 9], as well as the synovium [10]. Here, MS4A1 is linked to rheumatoid arthritis.