Peptidylarginine deiminases activity in synovial fluid samples from rheumatoid arthritis patients. (A) Synovial fluid (SF) samples from five rheumatoid arthritis patients were applied on enzyme-linked immunosorbent assay plates coated with fibrinogen (1 μg/ml) after 1:3 dilution into Tris buffer with 1 mM dithiothreitol (DTT; black columns), Tris buffer containing 1 mM DTT and 10 mM CaCl2 (grey columns) or Tris buffer containing 1 mM DTT and 10 mM ethylenediaminetetraacetic acid (EDTA; white columns). Following a 3-hour incubation period, the monoclonal mouse anti-citrullinated fibrinogen (anti-cFib) (0.5 μg/ml) was used for detection of citrullinated fibrinogen. Peptidylarginine deiminase (PAD) activity is presented as optical density (OD) at 490 nm of duplicated measurements. (B) Association between PAD2 concentration and PAD activity in the five SF samples diluted 1:3 in citrullination buffer containing 10 mM CaCl2 (grey circles, solid line) or no additive calcium (black circles, dotted line). Pearson’s correlation coefficients (r) and levels of significance are shown.