Antineutrophil cytoplasmic autoantibodies specific for myeloperoxidase cause glomerulonephritis and vasculitis in mice (1)
ANCAs are specific for antigens in the primary granules of neutrophils and the peroxidase- positive lysosomes of monocytes. The two major antigen specificities are for myeloperoxidase (MPO-ANCA) and proteinase 3 (PR3-ANCA).
ANCA IgG stimulates cytokine-primed neutrophils and monocytes to undergo respiratory burst, release toxic and lytic granule constituents, adhere to endothelial cells, and kill endothelial cells.
Rag2–/– mice that received anti-MPO splenocytes developed circulating anti-MPO (MPO- ANCA) within 3 days. The titer continued to rise until sacrifice at 13 days. Nonimmunized Mpo–/– mice that received 6.5 × 107 anti-MPO spleno- cytes had mean anti-MPO ELISA titers of 12.1, 75.6, 90.6, and 98.9 at days 0, 3, 8, and 13, respectively.
Rag2–/– mice that received 1 × 108 or 5 × 107 anti-MPO splenocytes developed severe renal failure that resulted in marked elevation of BUN and serum creatinine.
All Rag2–/– mice that received splenocytes developed urine abnormalities.
Crescents involved an average of 83.8% of glomeruli in mice that received 1 × 108 anti-MPO splenocytes (range 35–99%) and 85.0% in mice that received 5 × 10^7 anti-MPO splenocytes (range 48–99%). Necrosis was rare in mice that received anti-BSA or control splenocytes or 1 × 107 anti- MPO splenocytes.
The mean anti-MPO titer in WT B6 mice that received anti- MPOIgG was 109.5 one hour after injection, 100.7 after 3 days, and 98.7 after 6 days. By day 3, mice that received anti- MPO IgG already had developed hematuria, protein- uria, and leukocyturia, which persisted until sacrifice at day 6.
All six WT B6 mice sacrificed 6 days after receiving anti-MPO IgG had focal necrotizing glomerulonephritis (mean 4.7% of glomeruli with necrosis) and crescents (mean 3.3% of glomeruli with crescents). Immunofluo- rescence microscopy demonstrated little or no glomeru- lar staining for Ig’s, C3, or MPO in WT B6 mice that received anti-MPO IgG. Focal pulmonary alveolar capillaritis was identified in two of the six WT B6 mice that received anti-MPO IgG. Three of the WT B6 mice that received anti- MPO IgG had grossly discernible cutaneous lesions on the ears. Histologically, all three had focal ulceration and infarction. Necrotizing arteritis with fibrinoid necrosis and leukocytoclasia was identified in one specimen.
Either MPO-specific T lymphocytes or antibodies produced by MPO-specific B lymphocytes could be mediating the glomerulonephri- tis and vasculitis in the mice that received splenocytes. Pauci-immune characteristic of ANCA- associated glomerulonephritis is pathologically very distinct from the substantial vessel wall localization of Ig’s in immune complex–mediated glomerulonephritis and glomerulonephritis induced by anti–glomerular basement membrane (anti-GBM) antibody. ANCA IgG can activate neutrophils and monocytes in vitro. For example, ANCA IgG stimulates cytokine-primed neutrophils to release injurious oxygen metabolites and proteinases. Activation of neutrophils by ANCA IgG also induces the release of numerous proinflammatory cytokines, such as IL-1, IL-8, and leukotrienes. Monocytes also have ANCA antigens, including MPO and PR3, and can be induced to undergo a respiratory burst and release of proteinases and cytokines after stimulation by ANCA IgG. Neutrophils that have been activated by ANCA IgG are capable of adhering to and killing endothelial cells in vitro.