Pathogenesis of anti‐neutrophil cytoplasmic autoantibody (ANCA)‐associated vasculitis

Summary Anti‐neutrophil cytoplasmic autoantibody (ANCA)‐associated vasculitis is an autoimmune disease in which the contributions of genetic, epigenetic and environmental factors to aetiology and pathogenesis are being unravelled. The ANCA immunoglobulin G targeting proteinase 3 and myeloperoxidase affects several neutrophil functions, usually to augment or dysregulate these, promoting a proinflammatory phenotype whereby neutrophils have enhanced capabilities of causing collateral damage to endothelial and other cells. In addition, B cells are intimately involved in pathogenesis as anti‐B cell therapies are highly effective, but the manner of this involvement still needs to be delineated. Similarly, the T cell compartment is disturbed in ANCA vasculitis and numerous alterations in T cell subsets have been described, but recognition of a novel CD8+ T cell transcription signature which can predict likelihood of relapse in ANCA vasculitis indicates that more needs to be learnt about the influence of T cells in the disease process. Finally, the role of the alternative complement pathway and the potential therapeutic value of its neutralization is under active investigation after compelling studies in murine models have demonstrated that C5 and factor‐B knock‐out mice are protected.