Immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX) associated with pemphigoid nodularis: a case report and review of the literature

Immune dysregulation in primary immunodeficiency disorders

The past several years have brought an increased awareness of the prevalence of autoimmunity and immune dysregulation among patients who have primary immunodeficiency disorders (PIDD). The recent clinical and molecular definition of PIDD, in which the primary defect is in the immunoregulatory compartment of the immune system, has offered insight into the basic mechanisms of immune tolerance, which has provided new targets and new techniques to study immune tolerance in PIDD. Many of these studies have focused on the presence and function of regulatory T (T(REG)) cells in PIDD, particularly since the discovery of murine and human syndromes associated with T(REG) deficiency. This article focuses on the current state of knowledge regarding the role of T(REG) in various PIDD that have clinical features indicative of dysregulated immunity.

Primary immune deficiency disorders presenting as autoimmune diseases: IPEX and APECED

BACKGROUND

Several primary immune deficiency disorders are associated with autoimmunity and malignancy, suggesting a state of immune dysregulation. The concept of immune dysregulation as a direct cause of autoimmunity in primary immune deficiency disorders (PIDDs) has been strengthened by the recent discovery of distinct clinical entities linked to single-gene defects resulting in multiple autoimmune phenomena including immune dysregulation, polyendocrinopathy, enteropathy and X-linked (IPEX) syndrome, and autoimmune polyendocrinopathy, candidiasis and ectodermal dystrophy (APECED) syndrome.

CONCLUSION

Reviewing recent advances in our understanding of the small subgroup of PIDD patients with defined causes for autoimmunity may lead to the development of more effective treatment strategies for idiopathic human autoimmune diseases.

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked: forkhead box protein 3 mutations and lack of regulatory T cells

The rare X-linked disorder immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) and its murine counterpart scurfy have provided important new insights into the essential role of regulatory T cells (Treg) in maintaining tolerance to self-antigens. Mutations of the FOXP3 gene, identified in patients with IPEX, have helped pinpoint key structural domains of the protein that are essential for its function as a transcriptional regulator. Ongoing work using these and associated models has begun to elucidate factors important for the development, function, and competitive fitness of Treg. This improved understanding is beginning to lead to the identification of other defects that may be present in patients who have the clinical phenotype of IPEX but only wild-type FOXP3. It has also led to improved treatment options for IPEX including immunosuppressive drugs and bone marrow transplantation. We are hopeful that the knowledge gained about mechanisms that regulate FOXP3 expression and Treg function will have a major effect on how other autoimmune and allergic disorders are approached.

Severe food allergy as a variant of IPEX syndrome caused by a deletion in a noncoding region of the FOXP3 gene

BACKGROUND & AIMS

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX; OMIM 304930) syndrome is a congenital syndrome characterized by autoimmune enteropathy, endocrinopathy, dermatitis, and other autoimmune phenomena. In the present work, we aimed to uncover the molecular basis of a distinct form of IPEX syndrome presenting at the edge of autoimmunity and severe allergy.

METHODS

The FOXP3 gene was sequenced, FOXP3 messenger RNA (mRNA) was quantified by real-time polymerase chain reaction (PCR), and protein expression in peripheral blood lymphocytes was analyzed by flow cytometry after intracellular staining. In coculture experiments (CD4(+)CD25(-) and CD4(+)CD25(+) cells), the functions of regulatory T cells were analyzed. Expression of interferon gamma and interleukin 2 and 4 mRNA within the inflamed intestinal mucosa was quantified by real-time PCR.

RESULTS

Here, we describe a distinct familial form of IPEX syndrome that combines autoimmune and allergic manifestations including severe enteropathy, food allergies, atopic dermatitis, hyper-IgE, and eosinophilia. We have identified a 1388-base pair deletion (g.del-6247_-4859) of the FOXP3 gene encompassing a portion of an upstream noncoding exon (exon -1) and the adjacent intron (intron -1). This deletion impairs mRNA splicing, resulting in accumulation of unspliced pre-mRNA and alternatively spliced mRNA. This causes low FOXP3 mRNA levels and markedly decreased protein expression in peripheral blood lymphocytes of affected patients. Numbers of CD4(+)CD25(+)FOXP3(+) regulatory T cells are extremely low, and the CD4(+)CD25(+) T cells that are present exhibit little regulatory function.

CONCLUSIONS

A new mutation within an upstream noncoding region of FOXP3 results in a variant of IPEX syndrome associating autoimmune and severe immunoallergic symptoms.

Regulatory T cells in human autoimmune diseases

In the most simplistic terms, immune tolerance can be envisioned as a balance with autoreactive cells that arise naturally in all individuals on one side and regulatory mechanisms designed to counter those autoreactive processes on the other. A tilt of the balance toward the autoreactive side, either by increasing the number or function of autoreactive cells or by diminishing regulatory mechanisms, is manifested as autoimmunity. In contrast, tilting of the balance toward increased regulation could conceivably cause immunodeficiency. Regulatory T cells (T(REG)), and particularly the naturally arising CD4(+)CD25(+) subset of T(REG) cells, provide a substantial component of the autoimmune counterbalance. The identification of forkhead box P3 (FOXP3) as a critical determinant of CD4(+)CD25(+) T(REG) development and function has provided new opportunities and generated expanded interest in studying the delicate balance between autoimmunity and regulatory mechanisms in human autoimmune diseases. Identification of both human and mouse syndromes in which FOXP3 is mutated, and consequently CD4(+)CD25(+) T(REG) cells are absent, has led to a rapid accumulation of knowledge regarding T(REG) development and function over the past 5 years. The recent development of antibody reagents to specifically identify CD4(+)CD25(+) T(REG) cells by their FOXP3 expression has provided new tools to identify these elusive cells and investigate their role in human disease. This review will focus on the current state of knowledge regarding the role of T(REG) in human autoimmune diseases and on specific human immunodeficiencies that provide interesting models of autoimmunity.