The autoimmune regulator : Studies of immunological tolerance in mouse and man

The aim of the work presented in this thesis was to investigate how failure in the mechanisms that regulate self-tolerance can lead to autoimmune disease. In particular, I have studied a key player in immunological tolerance, the autoimmune regulator gene (AIRE). Mutations in this gene lead to a severe autoimmune disorder called autoimmune polyendocrine syndrome type I (APS I). APS I patients suffer from a combination of diseases caused by the immunological destruction of various tissues and organs, mainly the endocrine organs. The most common disease components are hypoparathyroidism, adrenocortical insufficiency and chronic mucocutaneous candidiasis (CMC). It has been clearly shown that AIRE is involved in the negative selection of autoreactive thymocytes. The suggested mechanism is that AIRE induce expression of tissue-specific antigens (TSAs) in the thymus that are needed for the deletion of autoreactive thymocytes, but the exact molecular events and relative importance of this are controversial. The first publication on which this thesis is based, reports that AIRE is involved in the regulation of T cell-independent B cell-responses, and that B cells in Aire mice have an increased activation status. This finding was thought to be connected to the increased serum levels of B cell activating factor of the TNF family (BAFF) found in both Aire mice and APS I patients. The excessive BAFF was produced by AIRE-deficient dendritic cells upon IFN-γ stimulation, which was independent of the presence of autoreactive T cells. It was suggested that AIRE regulates peripheral tolerance by inhibiting STAT1 signaling downstream of the IFN-γ receptor. The second paper describes how AIRE deficiency results in impaired development of iNKT cells, which may contribute to the pathogenesis of APS I. This finding suggests that AIRE has other functions apart from inducing TSAs in the thymus, given that iNKT cells recognize lipid antigens and are not dependent on ectopic peptide expression in the thymus for their development. In the third paper, the mechanisms behind CMC in APS I are described. It is shown that APS I patients have defects in innate immune mechanisms, i.e. the anti-fungal activity of the saliva. The patients exhibit IgA autoantibodies recognizing salivary glands as an indication of ongoing immunological destruction. Furthermore, they lack expression of salivary cystatin SA1, a protein with potent anti-fungal activity. The final paper describes investigations into possible mechanisms governing thymocyte development in the absence of AIRE. This was performed in a system independent of TSA expression where endogenous superantigens mediate selection and activation of transgenic T cells specific for an ovalbumin peptide presented by H2-IA (OT-II T cells). It was found that the OT-II T cells were reduced in Aire mice compared to wild type littermates, and showed an immature phenotype. It was also found that the OT-II Aire mice had increased TCR revision after activation in peripheral organs. The findings in Aire mice and APS I patients presented in this thesis are not explained by reduced TSA expression in the thymus. They show that AIRE has additional functions in both central and peripheral tolerance. LIST OF PUBLICATIONS I. Lindh, E. , Lind, S.M. , Lindmark, E. , Hässler, S. , Perheentupa, J., Peltonen, L. , Winqvist, O. , and Karlsson, M.C. I. (2008). AIRE regulates T cell independent B cell responses through BAFF Proc Natl Acad Sci U S A 105, 18466-18471. Highlighted in Nature Reviews Immunology, Jan 2009, vol 9. II. Lindh, E. , Rosmaraki, E. , Berg, L. , Brauner, H. , Karlsson, M.C. I. , Peltonen, L. , Höglund, P., and Winqvist, O. (2009). AIRE deficiency leads to impaired iNKT cell development J Autoimmunity. In print, doi:10.1016/j.jaut. 2009.07. 002 III. Lindh, E. , Brännström, J., Jones, P., Wermeling, F. , Karlsson, M.CI. , Hässler, S. , Stridsberg, M. , Herrmann, B. , Winqvist, O. Autoimmunity causes altered oral microenvironment and candidiasis in APS I In manuscript IV. Lindh. E. , Hässler, S. , Janson, P., Eberhardson, M. , Lindmark, E. , Karlsson, M.C. I. , Peltonen, L. , Winqvist, O. AIRE deficiency alters T cell selection and activation mediated by endogenous superantigens In manuscript LIST OF ABBREVIATIONS AADC AChR AD AIRE Aire AIRE ALPS APC APECED APS I BAFF BCR CBP CD CMC cTEC CTLA-4 CYP450 B6 DC DN DP FOB GAD HEL HLA HSR IA2 IFN IL IPEX iNKT MHC MS mTEC MZB NALP5 NOD PAMP PIAS/Pias PML RAG RIP Aromatic L-amino acid decarboxylase Acetylcholine receptor Addison’s disease Human autoimmune regulator gene Mouse autoimmune regulator gene Autoimmune regulator protein Autoimmune lymphoproliferative syndrome Antigen presenting cell Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy Autoimmune polyendocrine syndrome type I B cell activating factor of the TNF family B cell receptor CREB-binding protein Cluster of differentiation Chronic mucocutaneous candidiasis Cortical thymic epithelial cells Cytotoxic T lymphocyte antigen 4 Cytochrome P450 C57BL/6 Dendritic cell Double negative Double positive Follicular B cell Glutamate decarboxylase Hen egg lysozyme Human leukocyte antigen Homogeneously staining region Insulinoma associated tyrosine phosphatase like protein Interferon Interleukin Immunodysregulation, polyendocrinopathy and enteropathy, Xlinked Invariant natural killer T cell Major histocompatibility complex Multiple sclerosis Medullary thymic epithelial cells Marginal zone B cell NACHT leucine-rich-repeat protein 5 Non-obese diabetes Pathogen associated molecular patterns Protein inhibitor of activated STAT Promyelocytic leukemia bodies Recombination activating gene Rat insulin promoter SCC SLE SP STAT T1D TCR TSA tDC Treg 21-OH 17-OH Side chain cleavage enzyme Systemic lupus erythematosus Single positive Signal transducers and activator of transcription Type 1 diabetes T cell receptor Tissue-specific antigen Thymic dendritic cell T regulatory cell 21-hydroxylase 17α-hydroxylase