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‘Autoantigen complementarity’ is a theory proposing that the initiator of an autoimmune response is not necessarily the autoantigen or its molecular mimic, but may instead be a peptide that is ‘antisense/complementary’ to the autoantigen. We investigated whether such complementary proteins play a role in the immunopathogenesis of autoimmune glomerulonephritis. Experimental autoimmune glomerulonephritis, a model of anti-glomerular basement membrane (GBM) disease, can be induced in Wistar Kyoto (WKY) rats by immunization with the α3 chain of type IV collagen. In this study, WKY rats were immunized with a complementary α3 peptide (c-α3-Gly) comprised of amino acids that ‘complement’ the well characterized epitope on α3(IV)NC1, pCol(24–38). Within 8 weeks post-immunization, these animals developed cresentic glomerulonephritis, similar to pCol(24–38)-immunized rats, while animals immunized with scrambled peptide were normal. Anti-idiotypic antibodies to epitopes from c-α3-Gly-immunized animals were shown to be specific for α3 protein, binding in a region containing sense pCol(24–38) sequence. Interestingly, anticomplementary α3 antibodies were identified in sera from patients with anti-GBM disease, suggesting a role for ‘autoantigen complementarity’ in immunopathogenesis of the human disease. This work supports the idea that autoimmune glomerulonephritis can be initiated through an immune response against a peptide that is anti-sense or complementary to the autoantigen. The implications of this discovery may be far reaching, and other autoimmune diseases could be due to responses to these once unsuspected ‘complementary’ antigens.

This dissertation focuses on the interaction of antineutrophil cytoplasmic autoantibodies (ANCA) and two of their target autoantigens, myeloperoxidase and lysosomal membrane protein 2. The results of these interactions reveal novel epitopes associated with disease activity in granulomatosis with polyangiitis (GPA). The relationship between lysosomal membrane protein 2 (LAMP-2), a putative 3rd autoantigen, and ANCA disease is described in Chapter 1. In 2008, LAMP-2 was purposed to be a novel autoantigen which predicted relapse in ANCA disease. Exhaustive efforts uncovered that antibodies directed to LAMP-2 were not specific to ANCA disease nor were they relevant to disease activity in two US patient cohorts. Chapter 2 investigates the binding sites of myeloperoxidase (MPO) specific autoantibodies in sera samples from patients with ANCA glomerulonephritis and healthy controls. We proposed to prove the hypothesis that anti-MPO autoantibodies are restricted to a limited number of epitopes on MPO and whether circulating autoantibodies target the same epitopes during relapse and remission. In addition, to identify MPO epitopes of interest, a conformation dependent proteomics assay was used in conjunction with traditional immunologic methods. An ANCA disease associated epitope was uncovered (Chapter 3) with an association with disease activity. The discovery of this epitope has lead to the development of a preclinical test for ANCA disease (patent pending). As a whole, this is a comprehensive body of work which determines the complete profile of MPO specific epitopes found in a patient cohort in the southeastern US.