Anti-PCNA antibodies in psoriatic arthritis: a case-control study.

Objectives: Psoritic arthritis (PsA) is an inflammatory arthritis with infrequent antibodies. We present a case-control study of six PsA patients with antibodies against PCNA and observed clinical associations.

Methods: We conducted a study to identify autoantibodies in PsA. Sera from 81 PsA patients were assayed by immunoprecipitation from radiolabelled cell extracts. From this study, serum that immunoprecipitated a ≈32-kDa band was selected for mass spectrometry-based antibody discovery, which identified anti-PCNA antibodies. These were validated using immunoprecipitation of ³⁵S-methionine-labelled PCNA from in vitro transcription and translation. This assay tested 222 PsA sera for anti-PCNA antibodies. This study included sera from 39 healthy controls. Descriptive statistics were used to assess clinical associations with anti-PCNA status.

Results: Anti-PCNA antibodies were identified in 6/222 PsA patients. In 4/6 patients, banked longitudinal sera were available. In patients with anti-PCNA positivity compared with negativity, the mean age was 46 years (s.d. 14) and 52 years (s.d. 13), PsA disease duration was 8 years (s.d. 7) and 7 years (s.d. 8), BMI was 27 (s.d. 4) and 31 (s.d. 7), 67% and 44% were male, 100% and 89% were White, mean clinical DAPSA was 16 (s.d. 22) and 21 (s.d. 16), psoriasis body surface area was 2% (s.d. 4) and 5% (s.d. 12), HLA-B27 positivity was 0 and 12% and sulfasalazine (SSZ) use was 83% and 10%, respectively. Of these, only SSZ use was significant (Fisher's exact test P-value <0.001). Among anti-PCNA-positive patients with longitudinal sera, low/absent anti-PCNA coincided with articular low disease activity/remission.

Conclusion: Anti-PCNA antibodies were found in 6/222 (2.7%) PsA patients. Given the low prevalence of anti-PCNA, additional studies are needed to identify the clinical associations and significance.