Antineutrophil cytoplasmic antibodies (ANCA) and systemicvasculitis: update of assays, immunopathogenesis, controversies, and report of a novel de novo ANCA-associated vasculitis after kidney transplantation

Abstract

Objectives: To characterize antineutrophil cytoplasmic antibodies (ANCA),their major autoantigens, disease associations, and pathophysiology in systemic vasculitides. To describe a patient with a novel de novo ANCA-associated vasculitis after kidney transplantation. Methods: We reviewed and compiled the literature on ANCA-related topicsand systemic vasculitis. Laboratory and clinical data from a cadaveric kidney transplant patient who developed necrotizing vasculitis involving glomerular capillaries, with crescent formation associated with P-ANCA and myeloperoxidase, were analyzed. Results: Large-scale multi-center testing of patient and normal sera by theEuropean ANCA Assay Standardization Project using immunofluorescence assays and enzyme immunoassays indicate the assays have good sensitivity and specificity, and diagnostic utility for ANCA-associated vasculitis. A few investigations covering basic and clinical research with ANCA remain controversial: whether endothelial cells do or do not express a 29-kd neutral serine protease termed proteinase-3 (PR-3), the target of ANCA in most individuals with Wegener's granulornatosis, and whether anti-myeloperoxidase (MPO) ANCAs recognize a restricted number of epitopes on MPO. This issue has relevance for using monoclonal antibodies to treat patients with vasculitis who have adverse effects from immunosuppressive drugs. The two allelic forms of FcγRlla (H131/R131) and the two of FcγRlllb (NA1/NA2) are discussed as possible inheritable genetic elements for vasculitic disorders and for signaling responses. Stimulatory and costimulatory molecules, and cytokine profiles of T lymphocytes are characterized to show that these cells are actively involved in the ANCA-associated vasculitides. The patient described had a de novo ANCA associated small vessel vasculitis which developed after renal transplantation. Conclusions: There have been significant advances in the development ofsensitive and specific ANCA assays. The immunopathogenetic mechanism of ANCA involves the constitutive FcγRs, ligands, and signaling responses to activate cytokine-primed neutrophils. This may lead to the generation of reactive oxygen intermediates, degranulation, and secretion of intracellular granule contents, and ultimately inflammation and vasculitis.