DETECTION OF ANTINEUTROPHIL CYTOPLASMIC A NTIBODIES WITH PROTEINASE-3SPECIFICITY BY IMMUNOBLOTTING

Antineutrophil cytoplasmic antibodies (ANCA) are autoantibodies mainly directed against alpha granules' components (especially proteinase 3 (PR 3) and myeloperoxidase (MPO). They are usually detected by indirec t immunofluorescence (IIF) giving essentially two staining patterns, c ytoplasmic and perinuclear. Nevertheless the IIF method does not allow to precise the true specifity of ANCA. From now on a better classific ation of systemic vasculitis requires such a determination. This can b e done only by solid phase tests that require to be reliable, highly p urified antigen, and, from a practical point of view, only a MPO-ELISA is currently available. We report on our experience with Western blot analysis of 67 IIF-ANCA positive sera. Using Western blot analysis to characterize ANCA specificity is not so easy as in the case of antibo dies directed against extractable nuclear antigens : only PR 3 ANCA de tection could be done reproducibly. PR 3 ANCA are mainly detected in t he c-ACPN positive sera of patients with Wegener's granylomatosis. Nev ertheless using both MPO-ELISA and PR 3 blot seems to increase the fre quency of serum containing the two types of ANCA (anti PR 3 and anti M PO).