Experimental models of vasculitis and glomerulonephritis induced by antineutrophil cytoplasmic autoantibodies.

Antineutrophil cytoplasmic autoantibodies (ANCA) are closely associated with systemic small vessel vasculitis characterized by segmental vessel wall necrotizing inflammation and a paucity of immunoglobulin deposition. Clinically, in vitro and experimental animal model observations indicate a direct pathogenic role for ANCA. This review focuses on the results of experiments utilizing a mouse model of ANCA disease induced by transfer of mouse anti-MPO IgG or anti-MPO lymphocytes into recipient mice, which causes small vessel vasculitis and glomerulonephritis that closely mimics human disease. Evidence for the following conclusion about this model, and by implication about human ANCA disease, will be summarized as follows: (1) anti-MPO IgG is sufficient even in the absence of functional T cells to cause disease and anti-MPO T lymphocytes are not sufficient to cause acute injury; (2) neutrophils are required; (3) ANCA antigens in bone marrow-derived cells are sufficient targets; (4) increased circulating pro-inflammatory cytokines and microbial products exacerbate disease, and concurrent viral infection exacerbates and modulates the phenotype of disease; (5) Fcγ receptor engagement is required for disease induction, and Fcγ receptor repertoire modulates the phenotype of disease, especially pulmonary disease; (6) activation of the alternative pathway of complement is required, complement is activated by factors released by neutrophils stimulated by ANCA IgG and engagement of C5a receptors is a primary event in complement-mediated amplification; and (7) genetic background has a marked influence on the severity and outcome of disease, and modified gene expression in bone marrow-derived cells is the primary basis for genetically determined differences in disease susceptibility. Investigations using this animal model of ANCA disease have provided important insights into the cellular, molecular and genetic factors involved in the pathogenesis of ANCA disease which are likely to lead to the identification of improved markers of disease activity and response to therapy, as well as more effective and less toxic therapies.