IgA nephropathy with myeloperoxidase anti-neutrophil cytoplasmic antibodies (MPO ANCA): a discrepancy between the histological activity and MPO ANCA

Anti-neutrophil cytoplasmic antibodies (ANCA) of the immunoglobulin (Ig)G type are associated with rapidly progressive glomerulonephritis. Such antibodies have been detected only rarely in patients with Henoch-Schönlein purpura (HSP) or IgA nephropathy (IgAN). We report a patient with biopsy-proven IgAN with fibrous crescents in whom high titers of IgG ANCA occurred and were confirmed to be anti-myeloperoxidase antibodies (MPO ANCA) by solid-phase enzyme-linked immunosorbent assay (ELISA) and inhibition studies. During a 1-year follow-up period, high titers of MPO ANCA persisted but creatinine clearance remained over 50 ml/min per 1.48 m.² This case suggests the lack of a reliable association between fulminant outcome of IgAN with crescents and high titers of IgG MPO ANCA, and indicates the involvement of subsets of IgG MPO ANCA which recognize important or unimportant epitopes of MPO in the pathogenesis.