Animal models of anti-neutrophil cytoplasmic antibody-associated vasculitis(1).
Anti-neutrophil cytoplasmic antibody (ANCA) vasculitis is a severe systemic disease that affects joints, lungs, kidneys, skin and other tissues. It occurs most often in older adults and without treatment; mortality is approximately 80%. Myeloperoxidase (MPO) and proteinase 3 (PR3) shown subsequently as the autoantigens responsible for the perinuclear and cytoplasmic staining patterns, respectively.
To study pathogenesis of ANCA, animal models have been used. Early attempts at developing a rodent model showed that mercury chloride treatment of rats led to MPO antibodies in association with gut and cutaneous vasculitis. Immunity to MPO could exacerbate nephrotoxic nephritis, both through passive heterologous MPO antibody transfer and active immunization with human MPO (hMPO).
Autoimmune vasculitis in mice (model 4) involves the induction of both a humoral and cellular autoimmune response to MPO. This model was developed by the immunization of C57BL/6 mice with human MPO or mouse MPO, thus generating anti-MPO antibodies and cellular immunity which cross-react with murine MPO. Anti-MPO antibodies are lower levels compared to those seen in MPO-deficient mice, and immunization itself does not induce disease. The additional administration of glomerular binding antibody is required to attract neutrophils into the glomeruli. This glomerular binding antibody is a polyclonal antibody raised in sheep to a crude glomerular preparation and is the same as that used in the nephrotoxic nephritis model. This model has the advantage that there is an autoimmune response to MPO generated in wild-type mice. However, the requirement for a heterologous glomerular binding antibody to attract neutrophils into the glomerulus is a potential drawback, because large amounts of immune complexes are not usually present in the glomeruli of patients with ANCA vasculitis. Glomerular immune complexes can be detected by electron microscopy in approximately 50% of patients. Therefore this model has relevance as an ANCA vasculitis which involves autoimmune T cell response to cause glomerulonephritis.
ANCA target primarily MPO and PR3, both of which are present in the azurophilic granules of neutrophils and the peroxidase-positive lysosomes of monocytes. TLR stimulation can modulate T cell autoimmunity to MPO and influence disease expression. Using the autoimmune vasculitis model in mice (model 4), it was shown that IL-17A-deficient mice were protected from disease. TLR-2 ligation led to the generation of T helper type 17 (Th17) anti-MPO cells, whereas a Th1 response was favored by TLR-9 stimulation. MPO immunization with either TLR ligands resulted in glomerular inflammation and proteinuria. Contribution of complement, mice depleted of complement by treatment with cobra venom factor (CVF) were protected from disease induced by anti-MPO antibodies. In addition, treatment with an anti-C5 monoclonal antibody protected from disease in the same passive transfer model. This C5a is crucial to neutrophil priming for respiratory burst, as C5a receptor (C5aR) blockade during priming causes an inhibition of respiratory burst in response to ANCA.
