The Role of Complementary Proteins in Autoimmune Glomerulonephritis.

Although numerous theories exist proposing mechanisms whereby autoimmune diseases may be initiated, as of yet none of these have been definitively shown to be responsible for the induction of any naturally-occurring disease. One of these theories, known as autoantigen complementarity, states that the initiator of an autoimmune response may not be the target autoantigen itself or an exogenous mimic, but instead is a peptide or protein that is 'antisense' or 'complementary' in shape and/or charge to the autoantigen. The first immune response is therefore production of an antibody specific for this complementary protein, followed by an anti-antibody (i.e. anti-idiotypic antibody) that reacts with the paratope of the first antibody and also recognizes the 'sense' or self-protein due to surface contour, charge, and/or hydropathy complementarity. Our laboratory group has published evidence for autoantigen complementarity in one autoimmune glomerular disease, proteinase-3 specific antineutrophil cytoplasmic autoantibody glomerulonephritis. The overall objective of the work described here was to provide further evidence for complementary proteins as inciting antigens in autoimmune glomerulonephritis using anti-GBM disease as the classic antibody-mediated autoimmune glomerulopathy; our central hypothesis was that anti-GBM disease is caused by a protein or peptide complementary to the anti-GBM autoantigen. The design of synthetic peptides complementary in sequence to portions of the human and rat alpha3(IV)NC1 collagen domains, and the design and production of a recombinant complementary alpha3(IV)NC1 protein more likely to possess appropriate tertiary structure to be complementary in sequence and in structure to the full-length anti-GBM epitope are described. These antigens were used to demonstrate that a subset of patients with anti-GBM disease have anti-idiotypic antibodies specific for alpha3(IV)NC1-complementary peptides and proteins, that these antibodies are distinct from their pathogenic idiotypic partners, and that the anti-GBM antibodies bind to these anti-complementary protein antibodies as expected by idiotypic: anti-idiotypic partners. Finally, we describe the immunologic and clinicopathologic consequences of immunization of two rodent models with anti-GBM-complementary peptides, thus providing provisional evidence for autoantigen complementarity-induced anti-GBM disease.