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Vasculitic lesions are defined by necrosis of the vascular wall with perivascular inflammatory infiltrates. Secondary forms of vasculitis are observed in some systemic diseases, after infections, secondary to drugs or to malignancies. Usually, these secondary forms are characterised by the presence of immunoglobulin and complement deposits and thus probably caused by immune complex deposits. Conversely, necrotizing vasculitis occurring without known causal factor are named primary vasculitis, are not associated with immune deposits. Wegener's granulomatosis, microscopic polyangitis, Churg and Strauss syndrome and the isolated form of necrotizing and crescent glomerulonephritis are closely associated with the anti-neutrophil cytoplasm auto-antibodies (ANCA). The two main auto-antigen targets recognised by ANCA are lysosomal enzymes, proteinase 3 and myeloperoxidase, both contained in azurophilic granules of polymorphonuclear neutrophils and in primary lysosomes of monocytes. It has been demonstrated that ANCA antigens are expressed at the neutrophil (and monocyte) membrane after preactivation and are accessible to antibodies. Thus, ANCA may amplify neutrophils and monocyte activation. However, the causal or induced nature of anti-neutrophil auto-immunity in vasculitis remains unknown.

The specific antigens to antineutrophil cytoplasmic antibodies (ANCA) and their relations with renal diseases begin to be well-known. In patients with systemic vasculitis, two major antigens have been recognized: proteinase 3 and myoloperoxydase. These enzymes are located in the azurophilic granules of neutrophils and migrate to the surface of these cells when they are activated. Other antigens, such as elastase, lactoferrin, CAP57 and cathepsin G, have been identified, but they are less commonly encountered. The presence of ANCA is particularly frequent in Wegener's granulomatosis, microscopic periarteritis, crescentic necrotizing glomerulonephrites without immunoglobulin deposits; it is less frequent in periarteritis nodosa and in Churg-Strauss' syndrome. ANCA can now be considered as markers of vasculitis; they are related to disease activity and can be used to evaluate the effectiveness of treatments.