The IgG subclasses displayed by antibodies to four neutrophil cytoplasmic antigens were studied in 20 patients with systemic lupus erythematosus (SLE) by solid-phase enzyme immunoassays and monoclonal antibodies to human IgG subclasses. The IgG subclass reactivity of antineutrophil cytoplasmic antibodies (ANCA) was measured in six sera containing antiproteinase3 (PR3) antibodies, in five sera containing antimyeloperoxidase (MPO) antibodies, in sera containing antibactericidal/permeability-increasing protein (BPI) antibodies, and in ten sera containing antilactoferrin (LF) antibodies. The IgG subclass distribution of anti-dsDNA antibodies in eight sera was examined as well. IgGI was the predominant subclass for MPO-ANCA and LF-ANCA, whereas IgG1/IgG3 contributed mainly to anti-PR3, anti-BPI antibodies, and anti-dsDNA antibodies. In addition, we found elevated levels of the total IgG1 and IgG3 isotypes in the sera of our patients. Our results demonstrated a predominance of IgG1/IgG3 ANCA in SLE, suggesting that the isotype distribution of ANCA is a feature of antibody production in this disease.

Fifty-five patients with systemic lupus erythematosus (SLE) were examined for antineutrophil cytoplasmic antibodies (ANCA) by indirect immunofluorescence (IIF). Enzyme-linked immunosorbent assay (ELISA) for ANCA against myeloperoxidase (MPO), lactoferrin (LF), proteinase 3 (PR3), elastase (HLE), and bactericidal/permeability-increasing protein (BPI) was performed. The prevalence of ANCA by IIF was 29.1% (16/55 patients). MPO-ANCA were found in 10.9% (6/55), LF-ANCA in 18.2% (10/55), PR3-ANCA in 12.7% (7/55), BPI-ANCA in 23.6% (13/55), and HLE-ANCA in 1.8% (1/55). The levels of BPI-, LF-, and PR3-ANCA correlated with disease activity. A significant association between serositis and the presence of BPI-, LF-, and PR3-ANCA was observed, and PR3-ANCA were found to be associated with arthritis as well. Our results demonstrate that ANCA of various specificities occur in SLE, and BPI appears to be an important target antigen.