Predominance of IgG1 and IgG3 subclasses of autoantibodies to neutrophil cytoplasmic antigens in patients with systemic lupus erythematosus

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 11 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. IgG1 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.