CD68 and rheumatoid arthritis: Studies have shown that the cytological features of RA are very similar to the proliferating mononuclear synoviocytes in PVNS, and synovial cell proliferation appears to be a common feature in the pathogenesis of RA and PVNS (O’Keefe et al., 1998; Sarkissian and Lafyatis, 1999; Nanki et al., 2001), proliferating synovial cells can stimulate the expression of the macrophage marker CD68 (Aigner et al., 1998; Sarkissian and Lafyatis, 1999).