ACP5 and Arthritis: In patients with PsA, the circulating concentrations of TNF-α showed positive correlations not only with the number of TRAP+ osteoclast precursors (OCs) after culture with RANKL and M-CSF (r = 0.66; P = 0.000), but also with the radiographic damage scores (Sharp score r = 0.52; P = 0.001; BASRI r = 0.35; P = 0.02 ) and arthritis activity index PsAJAI (r = 0.41; P = 0.02).