Anti-cyclic citrullinated peptide antibodies and IL-23p19 in psoriatic arthritis

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Anti-cyclic citrullinated peptide antibodies (anti-CCP) are reported to be found in 5-13% of patients with psoriatic arthritis (PsA). However, whether anti-CCP-positive PsA patients and rheumatoid arthritis (RA) patients have a similar pathophysiological background still remains uncertain. To determine the prevalence of anti-CCP antibodies in patients with PsA and characterize these anti-CCP-positive patients of PsA. We measured the serum levels of the anti-CCP antibodies in patients with PsA (n=16), psoriasis (n=15), RA (n=9) and healthy controls (n=11). Serum levels of rheumatoid factor (RF), matrix metalloproteinase-3 (MMP-3), cartilage oligomeric matrix protein (COMP), interleukin (IL)-23p19 and IL-12p40 were also measured in all the samples. Two of the 16 PsA patients (13%) were positive for anti-CCP antibodies with high titers of RF. However, the serum IL-23p19 levels were two orders of magnitude higher in the anti-CCP-positive PsA patients as compared with those in the RA patients and anti-CCP-negative PsA patients. No significant elevation of the serum levels of MMP-3, COMP and IL-12p40 was found in these patients. Thirteen percent of the PsA patients were positive for anti-CCP. These patients do not fulfill the American College of Rheumatology (ACR) classification criteria for RA so far. Furthermore, they showed the typical clinical features of PsA rather than those of RA. Although anti-CCP-positive PsA patients may possibly be have a risk of developing RA, we propose that these patients be classified, for the moment, into a independent subtype of PsA, as a different entity from RA.