Antineutrophil cytoplasmic antibodies in systemic lupus erythematosus.

Antineutrophil cytoplasmic antibodies (ANCA) with specificity for proteinase-3 (PR3) are associated with Wegener's granulomatosis, and ANCA directed to myeloperoxidase (MPO) with other idiopathic vasculitides. Inflammation of small-sized blood vessels is a hallmark of systemic lupus erythematosus (SLE). We evaluated the prevalence of ANCA in SLE, their antigenic specificities, and their possible relation to clinical disease patterns and activity. Plasma samples from 84 patients with SLE were tested for ANCA during remission. Plasma samples from the 25 patients who relapsed during a follow-up of 32 months were serially analysed for ANCA in a 6 month period preceding and including the relapse. The presence of ANCA was assessed by indirect immunofluorescence (IIF) and ELISA for antibodies to PR3, MPO, lactoferrin (LF), elastase (HLE) and cathepsin-G (CG). We related the presence of ANCA to disease patterns, activity and duration. ANCA by IIF were difficult to interpret dut to the presence of antinuclear antibodies (ANA). By ELISA, we found no anti-PR3 or anti-HLE. Anti-MPO (n = 7), anti-LF (n = 13) and anti-CG (n = 10) were detected, generally in low titres. The presence of ANCA of defined specificity was not associated with specific clinical subsets. The prevalence of ANCA was higher in patients who developed relapses than in those who did not (P < 0.01). However, levels of ANCA did not fluctuate in the period preceding the relapse. ANCA of various specificities occur in SLE. Their presence is not associated with specific clinical disease entities. The higher frequency of ANCA in relapsing patients compared to those who do not relapse may suggest that ANCA are involved in disease expression. Their diagnostic significance is limited.