ACP5 and rheumatoid arthritis: TRAP+ cell counts were increased in the H2O2-stimulated RA-FLS-added group than in the H2O2 non-stimulated RA-FLS-added group, and TRAP+ cells decreased in a dose-dependent manner in DJ-1 10, 50, and 100 ng/mL pre-stimulated RA-FLS groups (Fig. 6A).