Associations of erosive arthritis with anti-cyclic citrullinated peptide antibodies and MHC Class II alleles in systemic lupus erythematosus.

OBJECTIVE: To determine the associations of erosive arthritis (EA) with anti-cyclic citrullinated peptide (anti-CCP) antibodies and major histocompatibility class (MHC) II alleles in systemic lupus erythematosus (SLE).
METHODS: One hundred four patients with SLE were evaluated for arthritis and classified as EA, nonerosive arthritis, or no arthritis. EA was further classified as major or minor erosions. Sera from patients and 130 serum controls were tested for anti-CCP2 and rheumatoid factor (RF). Patients and 117 genetic controls were genotyped for HLA-DRB1 and HLA-DQB1. Statistical associations were tested using chi-square tests and odds ratios (OR) with 95% confidence intervals (CI).
RESULTS: Eight patients (8%) were anti-CCP+ and they accounted for 11% (8/71) of patients with synovitis. Twelve patients (11%) had EA. Among patients with synovitis, EA was associated with anti-CCP (OR 28.5, 95% CI 4.7-173.8, p = 0.001), with a weaker association for RF (p = 0.3). Six patients with EA had major erosions and also met criteria for rheumatoid arthritis (RA). Four of these patients (67%) were anti-CCP+. HLA-DQB1*0302 was associated with EA (p = 0.01), with similar trends for HLA-DRB1*0401 and 2 copies of the shared epitope (SE). There were trends for associations of HLA-DQB1*0302 and 2 SE copies with anti-CCP production.
CONCLUSION: The frequency of EA in SLE is likely to be higher than previously reported. Anti-CCP+ patients with SLE are more likely to have EA. Anti-CCP may be a useful serological marker for EA for patients presenting with synovitis. Anti-citrulline antibodies may have a pathogenic role in the development of major erosions, resulting in clinical features that overlap SLE with RA (rhupus).