Anti-cyclic citrullinated peptide antibody determination in synovial fluid of psoriatic arthritis

OBJECTIVE: To assess the role of anti-CCP antibodies in synovial fluid (SF) of psoriatic arthritis (PsA) patients by analysing their association with different clinical patterns of the disease. METHODS: Seventy-five patients with a knee-joint effusion were studied, including 31 PsA patients, 29 rheumatoid arthritis (RA) and 15 osteoarthritis (OA) patients. SF and paired serum samples were stored at -70 degrees C until IgG anti-CCP and total IgG determination. The pattern of PsA articular involvement was defined as mono-, oligo-, polyarticular or axial. RESULTS: Lower levels of IgG anti-CCP antibodies in SF (p < 0.01) and serum (p < 0.005) were found in PsA respect to RA patients without difference with OA. We found a higher SF/serum ratio for anti-CCP compared to the SF/serum ratio for total IgG in PsA (p < 0.0005) as well as in RA and OA. The correction of anti-CCP concentration in SF as IgG anti-CCP (unit) / total IgG revealed lower (p < 0.002) values in PsA patients with respect to RA patients. In PsA group, values of anti-CCP antibodies, SF/serum ratio of anti-CCP and anti-CCP/IgG above the cut-off were found in 5, 6 and 2 SF samples respectively. The presence or absence of anti-CCP antibodies did not discriminate a particular clinical subset. CONCLUSIONS: In conclusion, strengthening the concept of local production of anti-CCP antibodies within the joint space, our results suggest that anti-CCP antibody detection in SF should take into account corrections such as total amount of corresponding immunoglobulin or SF/serum ratio. In our study, the presence or absence of anti-CCP antibodies did not discriminate a particular clinical subset, but further longitudinal studies are required to clarify the clinical role of anti-CCP in PsA.