Biomarker Discovery in Tissue-specific Autoimmune Disease

Abstract: Autoimmune diseases encompass a diverse group of disorders that collectively affect 5% of the population. Despite large clinical variability, autoimmune disorders share a common etiology in that they all develop from immune responses against self. T-cell receptors and antibodies recognize distinct self-molecules and direct destructive effector mechanisms to the target organs. Characterization of autoimmune targets can help in the understanding autoimmune disease features and is of additional importance for subsequent use in clinical diagnosis.Rare monogenic disorder can provide an access to the study and understanding of mechanisms underlying common and more complex diseases. Autoimmune polyendocrine syndrome type 1 (APS1) is an autosomal recessive disorder caused by mutations in the AIRE gene, and is a valuable model of tissue-specific autoimmune disease. APS1 patients develop multiple autoimmune disease manifestations and display autoantibodies against the affected tissues.Recent development in protein array technology has opened a novel avenue for explorative biomarker studies in autoimmune disorders. Present-day protein arrays contain many thousands of full-length human proteins and enable autoantibody screens at the proteome-scale.In the current work I have utilized proteome arrays to perform a comprehensive study of autoimmune targets in APS1. Survey of established autoantigens revealed highly reliable detection of autoantibodies, and by exploring the full panel of 9000 proteins we further identified three novel, major autoantigens. Our findings revealed a marked enrichment for tissue-specific immune targets and further suggest that only a very limited portion of the proteome becomes targeted by the immune system in APS1. This work identifies prostatic transglutaminase 4 as novel male-specific autoantigen. In the mouse model of APS1 we could link TGM4 immunity with a tissue-destructive prostatitis, a compromised prostatic secretion of TGM4 and with defect in the establishment of central immune tolerance for TGM4. Our findings suggest prostate autoimmunity is a major manifestation in male APS1 patients with potential role in development of subfertility. In this doctoral work we also report on collecting duct autoantibodies in APS1 patients with interstitial nephritis and on the identification of aquaporin 2 as a collecting duct autoantigen. Collectively, the present investigations provide an overview-perspective on the autoimmune target repertoire in APS1 and identify novel autoimmune manifestations of the syndrome.