ANTINEUTROPHIL CYTOPLASMIC AUTOANTIBODIES INTERACT WITH PRIMARY GRANULE CONSTITUENTS ON THE SURFACE OF APOPTOTIC NEUTROPHILS IN THE ABSENCEOF NEUTROPHIL PRIMING

The pathogenic role of antineutrophil cytoplasmic autoantibodies (ANCA ) remains controversial because of the difficulty in explaining how ex tracellular ANCA can interact with intracellular primary granule const ituents. It has been postulated that cytokine priming of neutrophils ( PMN), as may occur during a prodromal infection, is an important trigg er for mobilization of granules to the cell surface, where they may in teract with ANCA. We show by electron microscopy that apoptosis of unp rimed PMN is also associated with the translocation of cytoplasmic gra nules to the cell surface and alignment just beneath an intact cell me mbrane. Immunofluorescent microscopy and FACS(R) analysis demonstrate reactivity of ANCA-positive sera and antimyeloperoxidase antibodies wi th apoptotic PMN, but not with viable PMN. Moreover, we show that apop totic PMN may be divided into two subsets, based on the presence or ab sence of granular translocation, and that surface immunogold labeling of myeloperoxidase occurs only in the subset of PMN showing translocat ion. These results provide a novel mechanism that is independent of pr iming, by which ANCA may gain access to PMN granule components during ANCA-associated vasculitis.