SYSTEMIC INJECTION OF PRODUCTS OF ACTIVATED NEUTROPHILS AND H2O2 IN MYELOPEROXIDASE-IMMUNIZED RATS LEADS TO NECROTIZING VASCULITIS IN THE LUNGS AND GUT

The strong association of anti-neutrophil cytoplasmic antibodies with various forms of systemic vasculitis suggests a role for these autoant ibodies in the pathophysiology of systemic vasculitis. In the present study, we tested the hypothesis that release of neutrophil lysosomal e nzymes in the presence of an anti-myeloperoxidase (anti-MPO) immune re sponse may underlie the development of systemic vasculitis. Brown Norw ay rats were immunized with MPO in complete Freund's adjuvant or compl ete Freund's adjuvant alone. Two weeks after immunization, rats had de veloped antibodies to human and rat MPO as measured by enzyme-linked i mmunosorbent assay. Next, rats were intravenously infused with 400 mu g of a human neutrophil lysosomal extract containing 200 mu g of MPO f ollowed by 0.5 ml of a 1 mmol/L solution of H2O2 through a cannula ins erted into the right jugular vein. Rats were sacrificed at 4 hours, 24 hours, 7 days, or 14 days, and several organs (lungs, heart, liver, s pleen, gut, and kidneys) were examined for vasculitic lesions and infl ammatory cell infiltrates. Macroscopically, patchy hemorrhagic spots w ere observed in the lungs and gut of MPO-immunized rats at days 7 and 14 after systemic injection of the neutrophil lysosomal extract and H2 O2. Such changes were not observed at earlier time points or in contro l immunized rats. Histologically, the lungs of MPO-immunized rats sacr ificed at days 7 and 14 showed patchy inflammatory cell infiltrates as sociated with vasculitis, granuloma formation, giant cells, and foci o f hemorrhage. At 14 days, early signs of fibrosis were found with depo sition of collagen and proliferation of fibroblasts. Furthermore, a pr ominent leukocytoclastic vasculitis was found in the small intestine o f these rats characterized by fibrinoid necrosis and an extensive neut rophilic infiltrate. No inflammatory changes were found in the other o rgans studied (heart, liver, spleen, and kidneys). Controls immunized rats, sacrificed at days 7 and 14 showed only some small foci of infla mmatory infiltrates in the lungs whereas no inflammatory changes were found in the gastrointestinal tract. These studies show that release o f products from activated neutrophils in the presence of anti-MPO auto antibodies may be relevant to the pathogenesis of anti-MPO-associated vasculitides.