The substrate-binding domain of 21-hydroxylase, the main autoantigen in autoimmune Addison's disease, is an immunodominant T cell epitope

Epidemiology, pathogenesis, and diagnosis of Addison's disease in adults

BACKGROUND

Addison's disease (AD) is a rare disorder and among adult population in developed countries is most commonly caused by autoimmunity. In contrast, in children genetic causes are responsible for AD in the majority of patients.

PURPOSE

This review describes epidemiology, pathogenesis, genetics, natural history, clinical manifestations, immunological markers and diagnostic strategies in patients with AD. Standard care treatments including the management of patients during pregnancy and adrenal crises consistent with the recent consensus statement of the European Consortium and the Endocrine Society Clinical Practice Guideline are described. In addition, emerging therapies designed to improve the quality of life and new strategies to modify the natural history of autoimmune AD are discussed.

CONCLUSIONS

Progress in optimizing replacement therapy for patients with AD has allowed the patients to lead a normal life. However, continuous education of patients and health care professionals of ever-present danger of adrenal crisis is essential to save lives of patients with AD.

Autoimmune Addison's disease - An update on pathogenesis

Autoimmunity against the adrenal cortex is the leading cause of Addison's disease in industrialized countries, with prevalence estimates ranging from 93-220 per million in Europe. The immune-mediated attack on adrenocortical cells cripples their ability to synthesize vital steroid hormones and necessitates life-long hormone replacement therapy. The autoimmune disease etiology is multifactorial involving variants in immune genes and environmental factors. Recently, we have come to appreciate that the adrenocortical cell itself is an active player in the autoimmune process. Here we summarize the complex interplay between the immune system and the adrenal cortex and highlight unanswered questions and gaps in our current understanding of the disease.

Autoimmune Addison's disease

Addison's disease is a rare autoimmune disorder. In the developed world, autoimmune adrenalitis is the commonest cause of primary adrenal insufficiency, where the majority of patients have circulating antibodies against the key steroidogenic enzyme 21-hydroxylase. A complex interplay of genetic, immunological and environmental factors culminates in symptomatic adrenocortical insufficiency, with symptoms typically developing over months to years. Biochemical evaluation and further targeted investigations must confirm primary adrenal failure and establish the underlying aetiology. The diagnosis of adrenocortical insufficiency will necessitate lifelong glucocorticoid and mineralocorticoid replacement therapy, aiming to emulate physiological patterns of hormone secretion to achieve well-being and good quality of life. Education of patients and healthcare professionals is essential to minimise the risk of a life-threatening adrenal crisis, which must be promptly recognised and aggressively managed when it does occur. This article provides an overview of our current understanding of the natural history and underlying genetic and immunological basis of this condition. Future research may reveal novel therapeutic strategies for patient management. Until then, optimisation of pharmacological intervention and continued emphasis on education and empowerment of patients should underpin the management of individuals with autoimmune Addison's disease.

Association of genetic polymorphisms and autoimmune Addison's disease

Autoimmune Addison's disease (AAD) is a complex genetic disease that results from the interaction of a predisposing genetic background with as yet unknown environmental factors. The disease is marked by the appearance of circulating autoantibodies against steroid 21-hydroxylase. Mutations of the autoimmune regulator gene are responsible for the so-called autoimmune polyendocrine syndrome type I (APS I), of which AAD is a major disease component. Among genetic factors for isolated AAD and APS II, a major role is played by HLA class II genes: HLA-DRB1 0301-DQA1 0501-DQB1 0201 and DRB1 04-DQA1 0301-DQB1 0302 are positively, and RB1 0403 is negatively, associated with a genetic risk for AAD. The MHC class I chain-related gene A allele 5.1 is strongly and positively associated with AAD. Other gene polymorphisms contributing to genetic risk for AAD are MHC2TA, the gene coding for class II transactivator, the master regulator of class II expression, cytotoxic T lymphocyte antigen-4, PTPN22 and the vitamin D receptor.

T cell responses to steroid cytochrome P450 21-hydroxylase in patients with autoimmune primary adrenal insufficiency

CONTEXT

Autoimmune Addison's disease is thought to result from T cell mediated autoimmunity. Autoantibodies against the steroidogenic cytochrome P450 enzyme 21-hydroxylase (21OH) are found in most patients, and 21OH is therefore a likely target for antigen-specific T cells.

OBJECTIVE

The aim was to study cellular immunity to 21OH and its associations with 21OH autoantibodies and human leukocyte antigen alleles in autoimmune Addison's disease.

DESIGN/PATIENTS

Peripheral blood mononuclear cells were collected from 33 patients with autoimmune Addison's disease and 21 controls. Cellular proliferation and production of cytokines in response to stimulation with 21OH or 21OH-derived peptides were tested.

RESULTS

Cellular proliferation (P = 0.0009) and secretion of interferon-gamma (P < 0.0001) in response to 21OH was significantly higher in patients compared to healthy controls and associated with the presence of 21OH autoantibodies (P = 0.0052). Furthermore, the 21OH-specific production of interferon-gamma was enhanced in the presence of 21OH autoantibodies. This effect was partially inhibited by antibodies against the Fc receptor for IgG, CD32. Moreover, mature dendritic cells proved superior to the other antigen-presenting cells in invoking cellular responses to 21OH. An association between cellular immunity to 21OH and the high-risk HLA genotype for Addison's disease, DRB1*0301-DQ2/DRB1*0404-DQ8, was observed (P = 0.0089). Finally, a significant association between the DRB1*0404-DQ8 haplotype and cellular responses to a 21OH-derived peptide predicted to bind to DRB1*0404 was detected (P = 0.0055).

CONCLUSION

Patients with autoimmune Addison's disease have circulating 21OH-specific T cells, with amino acids 342-361 of 21OH possibly constituting a disease-specific epitope presented by HLA-DRB1*0404.

Recent advances in adrenal autoimmunity

Autoimmune Addison's disease (AAD) results from the immune-mediated destruction of adrenocortical cells. AAD is a major component of the autoimmune polyendocrine syndromes type 1 (APS 1) and type 2. The adrenal autoimmune process is made evident by the apperance of circulating autoantibodies against the steroidogenic enzyme 21-hydroxylase. Detection of 21-hydroxylase in patients with endocrine autoimmune diseases enables the identification of subjects with preclinical AAD. An impaired response to a corticotrophin stimulation test marks the irreversible stage of preclinical AAD and predicts progression towards clinical AAD in over 80% of cases. APS 1 is caused by mutations of the autoimmune regulator (AIRE) gene, which encodes an activator of transcription, Aire, that induces the expression of autoantigens in thymic medullary epithelial cells and promotes immunological tolerance. Isolated and APS 2-related AAD is an autoimmune disease with evidence for complex genetic susceptibility caused by T-cell-mediated destruction of adrenocortical cells, with a major contribution of HLA genes. The target cells in the adrenal cortex participate in the immune reaction by releasing chemokines, such as CXCL-10, that attract Th1 cells.

Immunology of Addison's disease and premature ovarian failure

Autoimmune Addison's disease and autoimmune ovarian insufficiency are caused by selective targeting by T and B lymphocytes to the steroidogenic apparatus in these organs. Autoantibodies toward 21-hydroxylase are a clinically useful marker for autoimmune Addison's disease. Autoantibodies to 21-hydroxylase are found in premature ovarian insufficiency, but others also can be present, notably antibodies against side-chain cleavage enzyme. The autoimmune response primarily targets the theca cells, yielding elevated concentrations of inhibin, which is emerging as a useful diagnostic marker for autoimmune etiology of ovarian insufficiency. Little is known about its immunogenetics, but in contrast to Addison's disease, several experimental models of autoimmune premature ovarian insufficiency are available for study.

Pathogenesis of primary adrenal insufficiency

Autoimmune Addison's disease is caused by autoreactivity towards the adrenal cortex involving 21-hydroxylase autoantibodies and autoreactive T cells. Autoimmune destruction of the adrenal cortex is triggered by hitherto unknown environmental factors in individuals with genetic susceptibility. Several genes have been identified, of which the major histocompatibility complex haplotypes DR3-DQ2 and DR4-DQ8 are most strongly associated. In addition, other genes also implicated in other autoimmune diseases are linked to Addison's disease, such as cytotoxic T lymphocyte antigen 4 (CTLA-4), protein tyrosine phosphatase non-receptor type 22 (PTPN22), major histocompatibility complex class II transactivator (CIITA), and most recently the C-lectin type gene (CLEC16A). Studies employing T cells in humans and animal models, and the collection of large patient cohorts facilitating genome-wide screening projects, will hopefully improve the understanding of the pathogenesis of the disease in the near future.

Identifying tumor antigens in endocrine malignancies

Tumor antigens are surface molecules that are mostly cancer specific, often overexpressed and recognized by the immune system. Therefore, identifying tumor antigens is of key importance for developing new immunotherapies for incurable cancers. For endocrine malignancies, several different tumor-associated antigens have been described, including polypeptide hormones and/or vesicle-associated antigens in Th1-mediated autoimmune diseases. Other antigens have been identified by screening tumor DNA libraries. Furthermore, vaccination studies in humans and animal models have revealed a tumor-antigen-specific immunity and clinical responses with reduced tumor size. Here, we provide an overview of the recent progress achieved in identifying tumor antigens and predict how this knowledge can be used in the future for developing anti-tumor vaccinations.

Fc? Receptor Polymorphisms are not Associated with Autoimmune Addison's Disease

Polymorphisms in the low-affinity Fcgamma receptors (FcgammaR) modulate their capacity to bind IgG and the subsequent immune response. Different FcgammaR polymorphisms have been reported to be associated with susceptibility and severity of various autoimmune diseases. We wanted to investigate associations between FcgammaR polymorphisms and autoimmune primary adrenal failure (Addison's disease). We have genotyped 149 patients with Addison's disease and 89 healthy controls for common polymorphisms in the genes coding for FcgammaRIIa, FcgammaRIIIa and FcgammaRIIIb using polymerase chain reaction. Patients with Addison's disease and controls showed no differences in genotype distributions of FcgammaRIIa, FcgammaRIIIa and FcgammaRIIIb. The results indicate that different FcgammaR polymorphisms do not have an impact on immune responses involved in the development of autoimmune Addison's disease.