Molecular characterization of human ANCA and antigen

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Anti-neutrophil cytoplasmic autoantibodies (ANCA) were first described in 1982. We reported the association of ANCA with necrotizing glomerulonephritis (GN) in 1988 and recognized myeloperoxidase (MPO)-ANCA. Since then, substantial insight into a number of issues has been gained including: 1) separation of ANCA antigens into MPO-ANCA or proteinase 3 (PR3)-ANCA; 2) clinical and pathological associations of ANCA with necrotizing GN and small vessel vasculitis (SVV); and 3) that ANCA participate in the pathogenesis of vascular inflammation. Despite these strides by the ANCA community little is known about the derivation of the human ANCA autoimmune response or the precise antigenic epitopes important in eliciting an autoimmune response during disease onset or during disease relapse. This project has three specific aims. The first aim studies the human PR3 and MPO-ANCA immunoglobulin gene expression. We hypothesize that MPO-ANCA and PR3-ANCA expression is dependent on specific light and heavy chain usage and that both MPO and PR3 are selecting antigens in the maturation of this autoimmune response. We developed a technique to amplify message from single B cells, allowing the study of somatic mutations of the amplified immunoglobulin genes. In the second aim, we will study specific epitopes on MPO and PR3 during disease onset and during relapse of ANCA-GN. Is the fine specificity of epitope usage during disease onset and relapse the same? We have clone fragments of MPO and PR3 into expression vectors to perform these studies. The third aim is the most exciting and may provide a new general understanding of autoimmunity and of the ANCA immune response in particular. It is known that peptides translated from the anti-sense strand of DNA bind to sense proteins with substantial selectivity and affinity. This concept is formulated as the molecular recognition theory. We have developed exciting preliminary data to support the novel concept that ANCA react not only with PR3, but also with complementary peptides to PR3. Is the immune response to the complementary peptide part of the autoimmune response? Are PR3-ANCA and antibodies to complementary peptides examples of an idiotypic anti-idiotypic relationship? We will have all the reagents necessary to explore this paradigm. The project will dissect human ANCA and ANCA antigens during disease onset and during disease relapse. We will ascertain whether the molecular recognition theory pertains to the human ANCA immune response in that ANCA may react, not only to PR3 and MPO, but to peptides complementary to these ANCA antigens.