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Anti-neutrophil cytoplasm autoantibodies (ANCA) is the preferred term for autoantibodies directed to myeloid cell cytoplasm and nuclear antigens, richly expressed in mature neutrophilic granulocytes and monocytes. When detected by indirect immunofluorescence technique (IIF) using ethanol-fixed neutrophils they can be divided into subcategories according to their reaction pattern with neutrophils:
C-ANCA (Fig. 1, see below) are defined as antibodies staining cytoplasmic granules, usually with accentuated intensity around the nucleus, P-ANCA (Fig. 2, see below) as antibodies staining the perinuclear cytoplasm and or the nucleus, and A-ANCA as any atypical staining pattern not fitting the C- or P-ANCA definitions (1). C-ANCA in patients with primary small vessel vasculitides (Wegener's granulomatosis, microscopic polyangiitis, Churg-Strauss syndrome) are mainly directed to the elastinolytic serine protease proteinase 3 (PR3), whereas P-ANCA in vasculitis patients mainly target the enzyme myeloperoxidase (MPO). In other inflammatory conditions that continuously engage neutrophils in the inflammation P-ANCA or A-ANCA may target a host of different proteins in neutrophil cytoplasm and/or nuclei (2).
The agreed IIF standard technique as well as an example of a standardized direct enzyme-immunoassay (EIA) for detecting PR3-ANCA and MPO-ANCA, respectively, is described in the following. These techniques were used in the European Union supported EC/BCR multicentre study on ANCA assay standardization, which demonstrated the feasibility of reaching standardization throughout Europe using three differently purified PR3 antigen preparations and one MPO preparation and very well defined method recipes (3). Most importantly, assay results were found to relate to the clinical vasculitic conditions for which the assays were designed (4). The EC/BCR study group formed the basis for the present European Vaculitis Study Group (EUVAS) which has continued the effort to build up of a large vasculitis patient serum bank in Copenhagen, Denmark.
 Figur 1 |
C-ANCA (cytoplasmic ANCA) is most commonly directed against the serine protease, proteinase 3 and strongly associated with Wegener's granulomatosis (click on the thumbnail to view the full-sized image). |
 Figur 2 |
P-ANCA (perinuclear ANCA) is more heterogeneous. It may be directed against myeloperoxidase (as seen most typically but not exclusively in microscopic polyangiitis), lactoferrin, elastase, cathepsin G and other antigens (click on the thumbnail to view the full-sized image). |