CD55 and rheumatoid arthritis: A study of cell surface expression, using flow cytometry, revealed that HA‐FLS (Figure S1A), non‐HA‐FLS (Figure S1B), RA‐FLS (Figure S1C) and HR‐FLS (Figure S1D) exhibited similar cell surface markers (CD45, CD55, CD68, CD90 and CD106), completely differing from the THP‐1 cell line (Figure S1E).8