Autoimmune Polyglandular Syndrome type 1 (APS-1) is caused by mutations in the Autoimmune Regulator (Aire) gene, which normally promotes central and peripheral T cell tolerance. APS-1 patients exhibit autoimmune disorders in multiple organs and a predisposition to chronic mucocutaneous candidiasis (CMC). A lack of mechanistic under- standing of the basis of candidiasis and its paradoxical association with autoimmunity hampers effective treatment of APS-1. Patients with candidiasis often have defects in cell-mediated immunity. APS-1 patients produce class- switched IgG autoantibodies against T helper 17 (TH17) cytokines, which may neutralize and impair protective anti- fungal immunity. This highlights humoral immune dysfunction as a potentially important contributing factor to CMC in APS-1. Our long-term goal is to understand the immune dysregulation in autoimmune and immunodeficiency disor- ders and to develop mechanism-guided therapeutic strategies. The objective in this application is to elucidate the mechanism of humoral immune defects in APS-1. Our preliminary studies show that AIRE is expressed specifically in human and mouse germinal center (GC) B cells in secondary lymphoid organs in vivo, and in B cells undergoing antibody diversification in vitro. AIRE deficiency in B cells causes elevated class switch recombination (CSR) and somatic hypermutation (SHM). AIRE suppresses CSR when introduced into AIRE-deficient B cells. AIRE interacts in B cells with activation-induced cytidine deaminase (AID), the enzyme essential for SHM and CSR. Aire?/? mice have aberrant expansion of GC B cell and T cell responses in systemic and mucosal lymphoid tissues. These findings support the central hypothesis that APS-1 involves aberrantly increased antibody maturation caused by B cell- intrinsic defects in AIRE-mediated AID regulation and B cell-extrinsic defects in the selection against autoreactive antibodies due to excessive GC response. Our rationale is that the elucidation of the mechanism of humoral immune defects in APS-1 will prompt more specific treatment of APS-1. The hypothesis will be tested by pursing two specific aims. Employing quantitative real-time PCR, flow cytometry, chromatin immunoprecipitation, genomic uracil dot blot and next-generation sequencing, studies in Aim 1 will determine the abnormalities in antibody maturation and the antibody repertoire in APS-1 and the mechanism by which AIRE regulates AID in B cells. Studies in Aim 2 will use competitive ELISA as well as mouse models of cutaneous Candida albicans infection to determine the role of B cell- intrinsic and -extrinsic AIRE deficiency in APS-1-associated candidiasis. This study proposes innovative and cutting- edge methodologies to test novel and mechanistic hypotheses in APS-1 pathogenesis. The work will have sustained and broad impact on the field of basic and clinical immunology, as it will not only advance the understanding of the disease APS-1 and AID-mediated regulation of antibody maturation, but also offer insights into the enigmas of an increasing number of immunodeficiencies that co-present with autoimmunity, thus paving the way to better treat the- se diseases.
The proposed research is relevant to public health and in line with the goals of this FOA by identifying novel pathogenic mechanisms of APS-1, a type IV primary immunodeficiency. The work will inform more effective treatment of this disease and also promote better understanding of other immunodeficiencies involving immune dysregulation. It therefore supports NIH's mission to seek fundamental knowledge to enhance health and reduce the burdens of illness and disability.
