A novel mouse model for MPO-ANCA-associated glomerulonephritis.(1)
Animal models have been used for studying the mechanisms for the development of vasculitis. The SCG/Kj mouse is a model of spontaneous crescentic glomerulonephritis (CrGN) associated with activated neutrophils. The MRL lpr/lpr strain, the background for the SCG/Kj mouse, is known to show high levels of MPO-ANCA in association with renal lesions, including GN and vasculitis. MPO-deficient model mice for coronary arteritis induced with Candida albicans-derived substances indicate that MPO is a major antigen for MPO-ANCA production. A mouse CrGN model with vasculitis was developed by serial injection of BSA. The mice showed three phases of renal damage: The initial phase: an increase of neutrophil and platelet counts and minor increase in MPO-ANCA, the second phase: proteinuria and glomerular neutrophil infiltration, the final phase: high MPO-ANCA and CrGN.
C57BL/6 mice received 0.2mg/mouse of BSA in complete Freund’s adjuvant by SC injection at 2-weeks intervals for 8 weeks, and subsequent daily intraperitoneal injection of 50 mg/kg BSA for 6 weeks, for a total 14 weeks. Proteinuria appeared in some mice 5 weeks after the first injection of BSA. Proteinuria continued to increase after 8 weeks from BSA injection, the number of mice with proteinuria and the levels of proteinuria showed a significant increase. Hematuria appeared later, with the frequency of hematuria rising 11–50% from 11 and 14 weeks after BSA injection.
At 9 weeks after the BSA injection, MPO-ANCA increased markedly. TNF-α also increased at 11 weeks after the BSA injection. Proteinuria was closely related to neutrophil infiltration into the glomeruli. Proliferative changes in GN were associated with the immune deposition of IgG, IgM, and C3 but not of IgA.
After an increase in the neutrophil counts in peripheral blood, neutrophils release lysosomal enzymes, mainly MPO, into the peripheral blood, then the MPO antibody may be produced to circulate into the peripheral blood. Therefore, increased neutrophil counts with proteinuria may play an essential role in glomerular injury. In rats, injection of rabbit anti-rat MPO antibodies into the rat clearly aggravates nephrotoxic serum nephritis. The administration of anti-MPO antibody induces both glomerular infiltration of activated neutrophils and elevation of proteinuria.
In the initial phase of BSA administration, before 8 weeks, an increase of the anti-BSA antibody may produce an immune complex, resulting in the activation of neutrophils to release lysosomal enzymes, mainly MPO, into the circulating blood. The MPO antibody is then produced to circulate into the blood from 4 weeks after the initial administration of BSA. Indeed, MPO itself has been reported to cause CrGN with proteinuria.