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Background
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Proteinase-3 is a lysosomal enzyme that can be found in human neutrophils. There are two subsets of autoantibodies to human neutrophils: c- ANCA and p-ANCA. The first subtype, c-ANCA, shows cytoplasmic staining by IFA and is diagnostic for Wegener's granulomatosis. The major antigen responsible for the c-ANCA staining is Proteinase-3. The second subtype, p-ANCA, shows perinuclear staining by IFA. The major antigen responsible for the p-ANCA response has been shown to be myeloperoxidase. The ANCA staining patterns are obtained using ethanol-fixed human neutrophils. Anti- PR-3 autoantibodies have been associated with Wegener's granulomatosis but less often with microscopic polyangiitis. Other antigen specificity's (CAP 57) can be responsible for the c-ANCA pattern. These antigens are generally not diagnostic for PR-3 associated vaculitus diseases.
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