Anti-myeloperoxidase autoantibodies in patients with necrotizing glomerular and alveolar capillaritis.

We conducted a prospective study of 651 Mediterranean patients from Catalonia (Spain) with well-defined forms of systemic vasculitis, connective tissue diseases, and renal and pulmonary disorders to determine the prevalence and clinical value of antineutrophil cytoplasmic autoantibodies (ANCA) with myeloperoxidase (MPO) specificity (MPO-ANCA). ANCA were first tested by indirect immunofluorescence on ethanol-fixed neutrophils. When a positive result was obtained, then MPO-ANCA were identified by performing the immunofluorescence assay again on neutrophils from a voluntary donor known to have a complete and selective deficiency of MPO. This disorder was detected by automated flow cytochemistry with the Technicon system and was further verified by cytochemical and biochemical studies. We detected MPO-ANCA in 61 of 70 (87%) patients with a perinuclear pattern (p-ANCA), but in none of 25 with a cytoplasmic pattern (c-ANCA). These results were corroborated by enzyme-linked immunosorbent assay (ELISA) using human purified MPO as a substrate. On immunofluorescence microscopy, all patients with MPO-ANCA were found to have a typical and restrictive immunostaining pattern. In our study, while c-ANCA were mainly found in patients with biopsy-proven Wegener's granulomatosis, MPO-ANCA identified those with idiopathic and polyarteritis nodosa-associated necrotizing and crescentic glomerulonephritis. In addition, pulmonary hemorrhage with necrotizing alveolar capillaritis as the main morphologic substrate occurred frequently among patients with MPO-ANCA, including three affected by polyarteritis nodosa and three who had pulmonary hemorrhage as the only clinical finding. On the other hand, these antibodies could be also detected in 30% of patients with a proven diagnosis of anti-glomerular basement membrane (GBM) disease.(ABSTRACT TRUNCATED AT 250 WORDS)