Anti-neutrophil cytoplasm autoantibodies (ANCA). The need for specific and sensitive assays

Anti-neutrophil cytoplasm antibodies (ANCA) are a group of autoantibodies primarily associated with systemic vasculitis. Hitherto, the method of choice for ANCA detection has been indirect immunofluorescence (IIF). By this method two major patterns can be seen: a cytoplasmic pattern (cANCA) or a perinuclear pattern (pANCA). The cANCA pattern is most often caused by antibodies directed against proteinase-3 (PR3) and in rare cases it is caused by anti-myeloperoixdase (MPO) antibodies. The pANCA pattern can de caused by antibodies directed against a large group of proteins i.e. MPO, lactofenin and bactericidal/permeability-increasing protein. Often there is a discrepancy between the results obtained by IIF and those reported from the use of assays with purified antigens. This causes confusion. Until now only anti-PR3 and anti-MPO have been found of any clinical value. Therefore, it would be more proper to use assays with these highly purified antigens instead of an unspecific method like IIF.