Anti-neutrophil cytoplasmic autoantibodies and patterns of pulmonary disease. A spectrum of pathologic findings.

In this issue of the American Journal of Clinical Pathology, Gaudin and colleagues report on their investigation of the spectrum of pulmonary lesions associated with anti-neutrophil cytoplasmic autoantibodies (ANCA). As various investigations have previously detailed, ANCAs are actually a heterogeneous collection of autoantibodies, which are for the most part directed at neutrophil granule enzymes. The two major target antigens are proteinase 3 (PR3), which produces a cytoplasmic pattern of staining by indirect immunofluorescence (CANCA), and myeloperoxidase (MPO), which produces a perinuclear pattern with this assay (P-ANCA). The study group of cases presented by Gaudin and colleagues consisted of 25 open lung biopsies and 2 autopsies, originating from 27 patients tested for ANCA. Thirteen of these 27 patients expressed CANCA, of which 12 of 12 tested were confirmed to have antiPR3 specificity. However, the 14 P-ANCA patients were all confirmed by ELISA assay to have anti-MPO antibodies. Capillaritis was common, and occurred with equal frequency in both P-ANCA and C-ANCA patients. Although airway lesions, necrotizing granulomas, and non-specific inflammation were more commonly seen in the C-ANCA patients, no single lesion was specific for either C-ANCA or P-ANCA. This study raises several interesting points, as detailed below: