Background/Purpose: Psoriatic arthritis (PsA) is an inflammatory joint disease with no serological biomarkers, hence diagnosis is based on clinical evaluation alone. PsA is closely associated with Psoriasis (PsO), with up to 1/3 of psoriatic patients developing PsA via unknown mechanism.

PsoP27 is an autoantigen found in skin lesions of PsO patients (1) and its levels correlate with psoriasis activity (2). PsoP27 is speculated to be involved in other inflammatory processes, yet it was not investigated in regard to PsA or RA.

The most common autoantigens in RA are citrullinated autoantigens which are formed by PAD  (peptidylarginine deiminase enzymes) and can drive the autoimmune response (3). Although known to be present in other diseases, citrullination is commonly associated with RA.

Our aim was to characterize native and citrullinated PsoP27 antibodies (Ab) in synovial fluids (SF) and sera of PsA and RA as compared to osteoarthritis (OA) patients and healthy controls, respectively.

Methods: SF of PsA (n=35), RA (n=11) and OA (n=13) patients and sera of PsA (n=32), RA (n=32) patients and healthy controls (n=31) were analyzed by ELISA for native and citrullinated PsoP27 Ab.

Results: In SF, both native and citrullinated PsoP27 Ab were significantly higher in PsA and RA compared to OA patients (Table 1). Significant correlation was observed between both forms of PsoP27 Ab in SF and swollen joints count (Native: p=0.029, r=0.39, Cit: p=0.041, r=0.369), psoriasis area and severity index (PASI) score (Native: p=0.011, r=0.56, Cit: p=0.008, r=0.369), and CRP levels (Native: p=0.017, r=0.446, Cit: p=0.03, r=0.408). In contrast, in RA patients there was no correlation between levels of PsoP27 Ab in SF and swollen joint count or CRP levels. No difference in PsoP27 Ab were detected in sera of all groups (Table 2).

Conclusion: We determined for the first time the presence of antibodies to psoriatic-related autoantigen PsoP27, in SF of PsA and RA patients. Furthermore, we showed a positive correlation between levels of PsoP27 Ab and disease activity in PsA, but not in RA. Also, we demonstrated the presence of citrullinated antibodies in PsA, commonly thought to be specific to RA. Our results suggest that PsoP27 Ab in SF may be utilized for diagnosis and disease assessment in PsA.

References:

1. Iversen OJ, Lysvand H, Jacobsen T, Bergh K, Lie BA. The psoriasis-associated antigen, pso p27, is expressed by tryptase-positive cells in psoriatic lesions. Arch Dermatol Res. 1995;287(5):503-5.
2. Dalaker M, Jacobsen T, Lysvand H, Iversen OJ. Expression of the psoriasis-associated antigen, Pso p27, is inhibited by cyclosporin A. Acta Derm Venereol. 1999;79(4):281-4.
3. Gudmann NS, Hansen NU, Jensen AC, Karsdal MA, Siebuhr AS. Biological relevance of citrullinations: diagnostic, prognostic and therapeutic options. Autoimmunity. 2015;48(2):73-9.

Table 1. PsoP27 Ab level (Optical Density, OD) in SF of PsA, RA and OA patients.

PsoP27 Ab level (OD) in sera of patients with psoriatic arthritis (PsA), rheumatoid arthritis (RA), and healthy controls (HC).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/identification-of-native-and-citrullinated-autoantibodies-to-psoriasis-related-antigen-psop27-in-synovial-fluids-of-patients-with-psoriatic-arthritis/