A 75-kD autoantigen recognized by sera from patients with X-linked autoimmune enteropathy associated with nephropathy

Pediatric autoimmune disorders with gastrointestinal expressions: from bench to bedside

The gastrointestinal (GI) tract may be involved in systemic autoimmune diseases or may be the target of organ-specific autoimmunity. Autoimmune enteropathy (AIE) is a rare disorder characterized by severe and protracted diarrhea, weight loss from malabsorption and immune-mediated damage to the intestinal mucosa, generally occurring in infants and young children, only rarely in adult. The salient histopathologic features of AIE are most prominent in the small intestine: villous blunting, crypt hyperplasia, mononuclear cell inflammatory expansion of the lamina propria with intraepithelial lymphocytosis, crypt apoptosis and absence of Paneth cells, goblet cells or both. Esophagus, stomach and colon are frequently also involved. Anti-enterocyte antibodies are identified in the majority of cases, and their presence, even if variable, can help confirming the diagnosis.

The purpose of this review is to provide an overview of the latest immunological advances in AIE, as well as to offer a practical approach for histological diagnosis for ‘general’ pathologist.

Intestinal Regulatory T Cells as Specialized Tissue-Restricted Immune Cells in Intestinal Immune Homeostasis and Disease

FOXP3+ regulatory T cells (Treg cells) are a specialized population of CD4+ T cells that restrict immune activation and are essential to prevent systemic autoimmunity. In the intestine, the major function of Treg cells is to regulate inflammation as shown by a wide array of mechanistic studies in mice. While Treg cells originating from the thymus can home to the intestine, the majority of Treg cells residing in the intestine are induced from FOXP3neg conventional CD4+ T cells to elicit tolerogenic responses to microbiota and food antigens. This process largely takes place in the gut draining lymph nodes via interaction with antigen-presenting cells that convert circulating naïve T cells into Treg cells. Notably, dysregulation of Treg cells leads to a number of chronic inflammatory disorders, including inflammatory bowel disease. Thus, understanding intestinal Treg cell biology in settings of inflammation and homeostasis has the potential to improve therapeutic options for patients with inflammatory bowel disease. Here, the induction, maintenance, trafficking, and function of intestinal Treg cells is reviewed in the context of intestinal inflammation and inflammatory bowel disease. In this review we propose intestinal Treg cells do not compose fixed Treg cell subsets, but rather (like T helper cells), are plastic and can adopt different programs depending on microenvironmental cues.

IPEX Syndrome: Improved Knowledge of Immune Pathogenesis Empowers Diagnosis

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare monogenic autoimmune disease with variable clinical manifestations, ranging from early-onset severe autoimmunity, including enteropathy, eczema, and type 1 diabetes, to late-onset or atypical symptoms. Despite the clinical heterogeneity, the unifying feature of IPEX is mutation of the FOXP3 gene, which encodes a transcription factor essential for maintenance of thymus-derived regulatory T cells (Tregs). In IPEX patients, Tregs can be present, although unstable and impaired in function, unable to inhibit proliferation and cytokine production of effector T (Teff) cells. Mutated FOXP3 can also disrupt other compartments: FOXP3-deficient Teff cells proliferate more than the wild-type counterpart, display altered T-cell-receptor signaling response, a reduced T-naïve compartment and a skew toward a Th2 profile. Due to FOXP3 mutations, the frequency of autoreactive B cells is increased and the IgA and IgE production is altered, together with early emergence of tissue-specific autoantibodies. Recently, the awareness of the wide clinical spectrum of IPEX improved the diagnostic tools. In cases presenting with enteropathy, histological evaluation is helpful, although there are no pathognomonic signs of disease. On the other hand, the study of FOXP3 expression and in vitro Treg function, as well as the detection of specific circulating autoantibodies, is recommended to narrow the differential diagnosis. Nowadays, Sanger sequencing should be limited to cases presenting with the classical triad of symptoms; otherwise, next-generation sequencing is recommended, given the cost-effectiveness and the advantage of excluding IPEX-like syndromes. The latter approach could be time spearing in children with severe phenotypes and candidate to advanced therapies.

A Review of Autoimmune Enteropathy and Its Associated Syndromes

Autoimmune enteropathy is an extremely rare condition characterized by an abnormal intestinal immune response which typically manifests within the first 6 months of life as severe, intractable diarrhea that does not respond to dietary modification. Affected individuals frequently present with other signs of autoimmunity. The diagnosis is made based on a characteristic combination of clinical symptoms, laboratory studies, and histological features on small bowel biopsy. Autoimmune enteropathy is associated with a number of other conditions and syndromes, most notably immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX) syndrome and autoimmune polyglandular syndrome type 1 (APS-1). Diagnosis and treatment is challenging, and further research is needed to better understand the pathogenesis, disease progression, and long-term outcomes of these conditions.

Updates in Pediatric Congenital Enteropathies: Differential Diagnosis, Testing, and Genetics

Congenital enteropathies comprise a heterogeneous group of disorders typically resulting in severe diarrhea and intestinal failure. Recent advances in and more widespread application of genetic testing have allowed more accurate diagnosis of these entities as well as identification of new disorders, provided a deeper understanding of intestinal pathophysiology through genotype-phenotype correlations, and permitted the exploration of more specific therapies to diseases that have heretofore been resistant to conventional treatments. The therapeutic armamentarium for these disorders now includes intestinal and hematopoietic stem cell transplantation, specific targeted therapy, such as the use of interleukin-1 receptor antagonists and, in some cases, gene therapy. These considerations are particularly applicable to the group of disorders identified as "very-early onset inflammatory bowel disease" (VEO-IBD), for which a veritable explosion of knowledge has occurred in the last decade. The pathologist plays a crucial role in assisting in the diagnosis of these entities and in ruling out other disorders that enter into the differential diagnosis.

Clinical, Immunological, and Genetic Features in Patients with Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) and IPEX-like Syndrome

BACKGROUND

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare inborn error of immunity caused by mutations in the forkhead box P3 (FOXP3) gene.

OBJECTIVE

In this study, we conducted a systematic review of patients with IPEX and IPEX-like syndrome to delineate differences in these 2 major groups.

METHODS

The literature search was performed in PubMed, Web of Science, and Scopus databases, and demographic, clinical, immunologic, and molecular data were compared between the IPEX and IPEX-like groups.

RESULTS

A total of 459 patients were reported in 148 eligible articles. Major clinical differences between patients with IPEX and IPEX-like syndrome were observed in rates of pneumonia (11% vs 31%, P < .001), bronchiectasis (0.3% vs 14%, P < .001), diarrhea (56% vs 42%, P = .020), and organomegaly (10% vs 23%, P = .001), respectively. Eosinophilia (95% vs 100%), low regulatory T-cell count (68% vs 50%), and elevated IgE (87% vs 61%) were the most prominent laboratory findings in patients with IPEX and IPEX-like syndrome, respectively. In the IPEX group, a lower mortality rate was observed among patients receiving hematopoietic stem cell transplantation (HSCT) (24%) compared with other patients (43%), P = .008; however, in the IPEX-like group, it was not significant (P = .189).

CONCLUSIONS

Patients with IPEX syndrome generally suffer from enteropathy, autoimmunity, dermatitis, eosinophilia, and elevated serum IgE. Despite similarities in their clinical presentations, patients with IPEX-like syndrome are more likely to present common variable immunodeficiency-like phenotype such as respiratory tract infections, bronchiectasis, and organomegaly. HSCT is currently the only curative therapy for both IPEX and IPEX-like syndrome and may result in favorable outcome.

Successful Salvage Haploidentical Alpha-Beta T Cell-Depleted Stem Cell Transplantation After Busulfan-Based Myeloablation in a Patient With IPEX Syndrome: A Case Report

BACKGROUND

X-linked immunodysregulation syndrome with polyendocrinopathy and enteropathy (IPEX) is caused by FOXP3 gene mutations that block the generation of regulatory T lymphocytes. We report an 18-month-old boy with classic IPEX who underwent 2 hematopoietic stem cell transplantations (HSCTs).

METHODS

The first HSCT from an unrelated 8/10 HLA-matched umbilical cord blood donor (UCB) was performed after a conditioning regimen consisting of treosulfan, fludarabine, thiotepa, and thymoglobulin. Due to complete rejection of the UCB transplant, a second transplantation from a 6/10 HLA-matched mother was performed after alpha-beta T-cell depletion. The second conditioning regimen consisted of busulfan, fludarabine, a single dose of cyclophosphamide 1 g/m², and Grafalon (Neovii Pharmaceuticals, Rapperswil, Switzerland). The T-cell depletion product contained 15.06 x 10⁶ CD34+ cells per kilogram body weight (BW) and 4.19 x 10⁵ alpha-beta T lymphocytes per kilogram BW. Due to acute graft rejection, the boy was treated with thymoglobulin, and full donor chimerism in both T lymphocytes and mononuclear cells was achieved. The immunosuppressive therapy was stopped 1 year after transplantation. To date, the patient remains free from graft-vs-host disease (GVHD) and immunosuppression.

CONCLUSIONS

HSCT after busulfan-based reduced-toxicity conditioning in patients with IPEX syndrome is feasible and well tolerated and can result in full donor engraftment. Monitoring of chimerism and aggressive therapy in cases of graft rejection are warranted due to the high reactivity of residual autologous T lymphocytes. T-cell depletion reduces the risk of GVHD and the need for steroid therapy, which is especially challenging in patients with diabetes.

Clinical Heterogeneity of Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-Linked Syndrome: A French Multicenter Retrospective Study

Objective

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is an autoimmune disease caused by mutations in the forkhead box protein 3 gene (FOXP3), which encodes a key regulator of immune tolerance. The aim of this study was to describe the clinical heterogeneity of the disease in a national French cohort.

Methods

Multicenter retrospective study of patients diagnosed with IPEX syndrome caused by mutations in FOXP3.

Results

Thirty children from 26 families were included. Age at disease onset (median [first to third quartile]) was 1.5 mo [0–84] and at death 3.5 years [0–10.5] (n = 15) indicating a high heterogeneity. Initial presentation was diarrhoea (68%), type 1 diabetes (T1D; 25%), skin lesions (7%) and nephropathy (3%). During the course of the disease the following main symptoms were observed: diarrhoea (100%), skin lesions (85%), T1DM (50%), severe food allergies (39%), haematological disorders (28%), nephropathies (25%), hepatitis (14%) as well as the presence of a variety of autoantibodies. Immunosuppressive mono- or combination therapy led to improvement in eight children. Three boys displayed a stable disease course without any immunosuppressive medication. Overall 10-year survival rate was 43% (42% in transplanted patients and 52% in patients on immunosuppressive therapy). Five out of 22 identified FOXP3 mutations have not been described yet: c.−23 + 1G > A, c.−23 + 5G > A, c.264delC, c.1015C > T and c.1091A > G. The first two produced atypical, attenuated phenotypes. Missense and frameshift mutations affecting the forkhead domain were associated with poor survival (Gehan–Wilcoxon p = 0.002).

Conclusion

The broad phenotypic heterogeneity of IPEX raises questions about modifying factors and justifies early FOXP3 sequencing in suspected cases.

Regulation of actin-based apical structures on epithelial cells

Cells of transporting epithelia are characterized by the presence of abundant F-actin-based microvilli on their apical surfaces. Likewise, auditory hair cells have highly reproducible rows of apical stereocilia (giant microvilli) that convert mechanical sound into an electrical signal. Analysis of mutations in deaf patients has highlighted the critical components of tip links between stereocilia, and related structures that contribute to the organization of microvilli on epithelial cells have been found. Ezrin/radixin/moesin (ERM) proteins, which are activated by phosphorylation, provide a critical link between the plasma membrane and underlying actin cytoskeleton in surface structures. Here, we outline recent insights into how microvilli and stereocilia are built, and the roles of tip links. Furthermore, we highlight how ezrin is locally regulated by phosphorylation, and that this is necessary to maintain polarity. Localized phosphorylation is achieved through an intricate coincidence detection mechanism that requires the membrane lipid phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] and the apically localized ezrin kinase, lymphocyte-oriented kinase (LOK, also known as STK10) or Ste20-like kinase (SLK). We also discuss how ezrin-binding scaffolding proteins regulate microvilli and how, despite these significant advances, it remains to be discovered how the cell polarity program ultimately interfaces with these processes.

Inflammatory bowel disease caused by primary immunodeficiencies-Clinical presentations, review of literature, and proposal of a rational diagnostic algorithm

Inflammatory bowel diseases (IBD) including Crohn's disease (CD) and ulcerative colitis have a multifactorial pathogenesis with complex interactions between polygenetic predispositions and environmental factors. However, IBD can also be caused by monogenic diseases, such as primary immunodeficiencies (PID). Recently, an increasing number of these altogether rare diseases have been described to present often primarily, or solely, as IBD. Early recognition of these conditions enables adaption of therapies and thus directly benefits the course of IBDs. Here, we discuss the different clinical presentations in IBD and characteristic features of patient's history, clinical findings, and diagnostic results indicative for a causative PID. Possible predictors are early onset of disease, necessity of parenteral nutrition, failure to respond to standard immunosuppressive therapy, parental consanguinity, increased susceptibility for infections, certain histopathologic findings, and blood tests that are atypical for classic IBD. We illustrate this with exemplary case studies of IBD due to NEMO deficiency, chronic granulomatous disease, common variable immunodeficiency, CTLA-4 and LRBA deficiency. Taking these factors into account, we propose a diagnostic pathway to enable early diagnosis of IBD due to PID.

Regulatory T Cell and Forkhead Box Protein 3 as Modulators of Immune Homeostasis

The transcription factor forkhead box protein 3 (FOXP3) is an essential molecular marker of regulatory T cell (Treg) development in different microenvironments. Tregs are cells specialized in the suppression of inadequate immune responses and the maintenance of homeostatic tolerance. Studies have addressed and elucidated the role played by FOXP3 and Treg in countless autoimmune and infectious diseases as well as in more specific cases, such as cancer. Within this context, the present article reviews aspects of the immunoregulatory profile of FOXP3 and Treg in the management of immune homeostasis, including issues relating to pathology as well as immune tolerance.

Mechanistic Basis of Organization of the Harmonin/USH1C-Mediated Brush Border Microvilli Tip-Link Complex

Brush border microvilli are actin-based protrusions lining the apical surface of epithelial cells in intestines and proximal tubules of kidneys. While brush border microvilli resemble the relatively well-characterized stereocilia of hair cells, the mechanistic basis of tip-link complex organization in microvilli is poorly understood. Here, we have biochemically and structurally characterized the following pairs of interactions: protocadherin 24 and Harmonin (also known as USH1C or AIE-75), Harmonin and myosin VIIb (MYO7B), Harmonin and ANKS4B, and ANKS4B and MYO7B. We show that Harmonin, ANKS4B, and MYO7B form a stable ternary complex for anchoring microvilli tip-link cadherins. Despite having only Harmonin in common, the microvilli and the stereocilia tip-link complexes are formed via strikingly similar interaction modes. These results not only provide insight into the mechanistic bases of brush border microvilli formation and maintenance but may also be valuable for understanding some gut and/or kidney diseases caused by perturbations of brush border microvilli structures.

Patterns of Allergic Sensitization in High IgE Syndromes

Dramatic elevations in the serum IgE level are seen both in polygenic allergic diseases such as atopic dermatitis and food allergy, and in a growing list of monogenic primary immune deficiencies (PIDs). Although the IgE produced in patients with PID has generally been considered to be driven by dysregulated IL-4 production and thus lack antigen specificity, in fact allergen-specific IgE can be detected by skin and serum testing in many of these patients. However, perhaps not surprisingly given the distinct immunologic pathways involved, the patterns of allergic disease and atopic sensitization vary widely between syndromes, leading to strikingly different clinical phenotypes.

Gene/cell therapy approaches for Immune Dysregulation Polyendocrinopathy Enteropathy X-linked syndrome

Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) syndrome is a rare autoimmune disease due to mutations in the gene encoding for Forkhead box P3 (FOXP3), a transcription factor fundamental for the function of thymus-derived (t) regulatory T (Treg) cells. The dysfunction of Treg cells results in the development of devastating autoimmune manifestations affecting multiple organs, eventually leading to premature death in infants, if not promptly treated by hematopoietic stem cell transplantation (HSCT). Novel gene therapy strategies can be developed for IPEX syndrome as more definitive cure than allogeneic HSCT. Here we describe the therapeutic approaches, alternative to HSCT, currently under development. We described that effector T cells can be converted in regulatory T cells by LV-mediated FOXP3-gene transfer in differentiated T lymphocytes. Despite FOXP3 mutations mainly affect a highly specific T cell subset, manipulation of stem cells could be required for long-term remission of the disease. Therefore, we believe that a more comprehensive strategy should aim at correcting FOXP3-mutated stem cells. Potentials and hurdles of both strategies will be highlighted here.

Autoantibodies to harmonin and villin are diagnostic markers in children with IPEX syndrome

Autoantibodies to enterocyte antigens harmonin (75 kDa USH1C protein) and villin (actin-binding 95 kDa protein) are associated with the Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) syndrome. In this study we evaluated the diagnostic value of harmonin and villin autoantibodies in IPEX and IPEX-like syndromes. Harmonin and villin autoantibodies were measured by a novel Luminescent-Immuno-Precipitation-System (LIPS) quantitative assay, in patients with IPEX, IPEX-like syndrome, Primary Immunodeficiencies (PID) with enteropathy, all diagnosed by sequencing of the FOXP3 gene, and in type 1 diabetes (T1D), celiac disease and healthy blood donors as control groups. Harmonin and villin autoantibodies were detected in 12 (92%) and 6 (46%) of 13 IPEX patients, and in none of the IPEX-like, PID, T1D, celiac patients, respectively. All IPEX patients, including one case with late and atypical clinical presentation, had either harmonin and/or villin autoantibodies and tested positive for enterocyte antibodies by indirect immunofluorescence. When measured in IPEX patients in remission after immunosuppressive therapy or hematopoietic stem cell transplantation, harmonin and villin autoantibodies became undetectable or persisted at low titers in all cases but one in whom harmonin autoantibodies remained constantly high. In one patient, a peak of harmonin antibodies paralleled a relapse phase of enteropathy. Our study demonstrates that harmonin and villin autoantibodies, measured by LIPS, are sensitive and specific markers of IPEX, differentiate IPEX, including atypical cases, from other early childhood disorders associated with enteropathy, and are useful for screening and clinical monitoring of affected children.

Autoimmune enteropathy: a review and update of clinical management

Autoimmune enteropathy (AIE) is a rare condition characterized by intractable diarrhea, histologic changes on small intestinal biopsy, and failed response to dietary manipulation that also may present with extraintestinal manifestations. In many patients, immunosuppressive therapies are necessary. Although AIE is more common in infants, adult involvement has also been documented. Much of what is known about AIE has been gathered from case reports and small case series; therefore, more research in this evolving field is needed. IPEX (immunodysregulation polyendocrinopathy enteropathy X-linked syndrome) and APECED (autoimmune phenomena, polyendocrinopathy, candidiasis, and ectodermal dystrophy) are systemic forms of AIE.

Autoimmune enteropathy: a review and update of clinical management

Autoimmune enteropathy (AIE) is a rare condition characterized by intractable diarrhea, histologic changes on small intestinal biopsy, and failed response to dietary manipulation that also may present with extraintestinal manifestations. In many patients, immunosuppressive therapies are necessary. Although AIE is more common in infants, adult involvement has also been documented. Much of what is known about AIE has been gathered from case reports and small case series; therefore, more research in this evolving field is needed. IPEX (immunodysregulation polyendocrinopathy enteropathy X-linked syndrome) and APECED (autoimmune phenomena, polyendocrinopathy, candidiasis, and ectodermal dystrophy) are systemic forms of AIE.

Immune dysregulation, polyendocrinopathy, enteropathy, x-linked syndrome: a paradigm of immunodeficiency with autoimmunity

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare monogenic primary immunodeficiency (PID) due to mutations of FOXP3, a key transcription factor for naturally occurring (n) regulatory T (Treg) cells. The dysfunction of Treg cells is the main pathogenic event leading to the multi-organ autoimmunity that characterizes IPEX syndrome, a paradigm of genetically determined PID with autoimmunity. IPEX has a severe early onset and can become rapidly fatal within the first year of life regardless of the type and site of the mutation. The initial presenting symptoms are severe enteritis and/or type-1 diabetes mellitus, alone or in combination with eczema and elevated serum IgE. Other autoimmune symptoms, such as hypothyroidism, cytopenia, hepatitis, nephropathy, arthritis, and alopecia can develop in patients who survive the initial acute phase. The current therapeutic options for IPEX patients are limited. Supportive and replacement therapies combined with pharmacological immunosuppression are required to control symptoms at onset. However, these procedures can allow only a reduction of the clinical manifestations without a permanent control of the disease. The only known effective cure for IPEX syndrome is hematopoietic stem cell transplantation, but it is always limited by the availability of a suitable donor and the lack of specific guidelines for bone marrow transplant in the context of this disease. This review aims to summarize the clinical histories and genomic mutations of the IPEX patients described in the literature to date. We will focus on the clinical and immunological features that allow differential diagnosis of IPEX syndrome and distinguish it from other PID with autoimmunity. The efficacy of the current therapies will be reviewed, and possible innovative approaches, based on the latest highlights of the pathogenesis to treat this severe primary autoimmune disease of childhood, will be discussed.

Autoantibodies to villin occur frequently in IPEX, a severe immune dysregulation, syndrome caused by mutation of FOXP3

Intractable diarrhea is a major symptom of immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome and associated with autoantibodies against enterocytes. Although autoimmune enteropathy (AIE)-related 75 kDa antigen (AIE-75) is a prominent autoantigen involved in the enteropathy associated with IPEX syndrome, some patients with this syndrome demonstrated autoantibody recognizing a 95 kDa protein rather than AIE-75 in the small intestine. We, herewith, identified villin, an actin-binding protein, as the 95 kDa antigen. Four of five sera from patients with IPEX syndrome reacted with a fusion protein of glutathione-S-transferase and full length villin (GST-villin), whereas only three of 98 control sera weakly reacted with GST-villin. Anti-AIE-75 antibody was detected in all five IPEX sera but not in normal or control disease sera. We conclude that both AIE-75 and villin appear to be brush border autoantigens in IPEX syndrome and could be used for the diagnosis of AIE in patients with presumptive IPEX syndrome.

Enteropathies of Infancy and Childhood

Intestinal biopsies constitute an ever-increasing portion of the pathologist's workload, accounting for nearly two-thirds of specimens accessioned yearly by the pathology department at The Children's Hospital of Philadelphia. The widespread use of endoscopy and gastrointestinal biopsies in current clinical practice presents the pathologist with a diversity of intestinal mucosal appearances corresponding to disease states of variable clinical severity, requiring close collaboration between clinician and pathologist for optimal interpretation. Many of the entities resulting in severe diarrhea of infancy have been recognized only in the last several decades, and although rare, the study of these disorders, especially when combined with the powerful methods of present-day genetics and molecular biology, has afforded important insights into enterocyte development and function, and intestinal immunity and tolerance. Other conditions once considered infrequent, such as celiac disease, have now been recognized to be much more common and can present with a wide range of pathologic features.

Autoimmune enteropathy in children and adults

Autoimmune enteropathy is a rare disorder characterized by severe and protracted diarrhea, weight loss from malabsorption and immune-mediated damage to the intestinal mucosa, generally occurring in infants and young children, although some cases of adult onset have been reported in the literature. Pathogenetic mechanisms involve immunological disorders, in which the presence of antienterocyte autoantibodies, although detected since first description, seems now to be secondary. As occurs frequently in autoimmunity, subjects with autoimmune enteropathy may be affected by other autoimmune disorders, sometimes leading to particular forms, i.e. the IPEX syndrome and the APECED syndrome. The prognosis of autoimmune enteropathy patients depends on the severity of digestive symptoms (including fecal output), on the severity and extension of histological lesions along the gastrointestinal apparatus, and on the presence of extra-intestinal involvement. Management of autoimmune enteropathy patients is based on nutritional support and adequate hydration to ensure optimal growth and development, together with immunosuppressive therapy. Recently, biological agents have been introduced, with apparent beneficial effects.

From autoimmune enteropathy to the IPEX (immune dysfunction, polyendocrinopathy, enteropathy, X-linked) syndrome

The term autoimmune enteropathy (AIE) was applied to a form of "intractable diarrhoea" with serum gut autoantibodies, characterized by male predominance, early onset, poor response to parenteral nutrition and several autoimmune diseases, mainly type 1 diabetes. In recent years the vague concept of AIE has became more precise thanks to the discovery of its genetic and molecular basis. The FOXP3 molecule is crucial for the generation and maturation of regulatory T cells (Treg) expressing CD4+ and CD25+ molecules. Mutations of the FOXP3 gene, located in X chromosome, produce a syndrome with Immune dysfunction, Polyendocrinopathy, Enteropathy and X-linked inheritance (IPEX). The majority of the ancient so-called AIE cases probably correspond to the new IPEX syndrome, even in female patients who may have some autosomal genetic variants. Besides FOXP3, other molecules are likely to be involved in the generation and function of Treg and its deficiency may also enhance autoimmune disease and IPEX-like syndromes. Meanwhile, the important pathogenic role previously ascribed to gut autoantibodies has vanished, with it remaining as having only certain screening usefulness.

Digestive histopathological presentation of IPEX syndrome

Immunodysregulation, polyendocrinopathy, enteropathy, and X-linked inheritance (IPEX) syndrome is a well recognized and particularly severe form of autoimmune enteropathy. It has an X-linked recessive transmission, and is caused by mutations in the FOXP3 gene. We studied the intestinal morphological changes characterizing IPEX syndrome in a series of 12 children with a molecularly confirmed diagnosis. Histological examination of duodenal, gastric and colonic biopsies were retrospectively reviewed and compared by two independent experienced pathologists. In parallel, the presence of circulating anti-enterocyte antibodies was analysed using an indirect immunofluorescence technique and a quantitative radioligand assay against the 75-kDa autoantigen. The morphology of the inflammatory gut lesions could be categorized into three different entities, namely graft-vs-host disease-like changes (9/12 patients), a coeliac disease-like pattern (2/12) and an enteropathy with a complete depletion of goblet cells (1/12). Our results do not suggest any phenotype-genotype correlation. Circulating antibodies were detected in all 12 patients, with an anti-brush border pattern (11/12) and anti-goblet cell antibodies (1/12), as well as by a radioligand assay. The histological presentation of autoimmune enteropathy is rather variable. However, a graft-vs-host disease-like pattern associated with positive anti-enterocyte antibodies is the most frequent intestinal presentation of IPEX syndrome, and constitutes a very valuable tool for pathologists to suspect this diagnosis.

Autoimmune enteropathy in Swedish children, 1985-2002: a call for strict diagnostic criteria

OBJECTIVE

To investigate the incidence, prevalence and the long-term outcome of autoimmune enteropathy in Sweden.

MATERIAL AND METHODS

In 2002 a questionnaire was sent to all paediatric departments in Sweden asking them to report all known cases of this condition from the period 1985-2002.

RESULTS

The response rate was 92%. Five patients were reported and 3 were included in the study. Only one patient fulfilled all the diagnostic criteria and two were considered as possible cases of autoimmune enteropathy. The incidence was 0.06 to 0.12 x 10(-5) and the prevalence was 0.05 to 0.10 x 10(-5) for children aged 0-16 years. At the end of the study period all 3 patients were still alive. Two boys were receiving immunosuppressive treatment and one girl was in remission and functioning well on a gluten-free diet only. One of the patients had adrenalitis. This combination has not been reported previously in autoimmune enteropathy.

CONCLUSIONS

Autoimmune enteropathy in its severe forms is a rare disease in Sweden. None of the patients reported died during the study period. Comparative studies are difficult as different diagnostic criteria are used to diagnose this disease.

Regulatory T cells in primary immunodeficiency diseases

PURPOSE OF REVIEW

Several primary immune deficiency disorders are associated with autoimmunity and malignancy, suggesting a state of immune dysregulation. Here, we review the role of regulatory T-cell deficits in mediating the immune dysregulation associated with certain primary immune deficiency disorder syndromes.

RECENT FINDINGS

Systematic studies in primary immune deficiency disorders and their associated animal models have led to an increased understanding of both central and peripheral tolerance mechanisms, and in particular have yielded new insights into regulatory T-cell function, development and maintenance.

SUMMARY

Single-gene defects identified in patients with multiple autoimmune phenomena have defined new primary immune deficiency disorder syndromes in which the primary deficit is in the establishment or maintenance of immune tolerance. The disorder that has been most informative with regard to understanding the function and development of regulatory T cells is forkhead box P3 deficiency, known as immune dysregulation, polyendocrinopathy, enteropathy and X-linked syndrome in humans and Scurfy in the mouse. Recent studies in patients with other primary immune deficiency disorders, including autoimmune polyendocrinopathy, candidiasis and ectodermal dystrophy syndrome, CD25 deficiency, STAT5b deficiency, and Wiskott-Aldrich syndrome, have added to our understanding of regulatory T-cell biology. The study of patients with rare primary immune deficiency disorder syndromes provides an unparalleled opportunity to understand mechanisms of autoimmunity and immune tolerance in humans.

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.

Immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome: an unusual cause of proteinuria in infancy

We report on a 6-month-old child presenting with chronic diarrhea, failure to thrive, eczema, autoimmune hemolytic anemia (AIHA), insulin-dependent diabetes mellitus (IDDM), hypoalbuminemia, and proteinuria. Renal biopsy showed membranous glomerulonephritis. A diagnosis of Immunodysregulation, polyendocrinopathy, enteropathy, x-linked (IPEX) syndrome was subsequently confirmed by DNA analysis, which demonstrated the presence of a mutation in exon 2 of the FOXP3 gene (303-304 del TT). Proteinuria secondary to membranous glomerulonephritis is a novel feature of IPEX syndrome. Membranous glomerulonephritis went into remission after the patient had received hematopoietic stem cell transplantation (HSCT).

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.

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked inheritance: model for autoaggression

Patients with the rare X-linked syndrome, immune dysregulation, polyendocrinopathy, enteropathy (IPEX) may present early in life with type I diabetes, hyperthyroidism, chronic enteropathy, villous atrophy, dermatitis, autoimmune hemolytic anemia, and antibody- induced neutropenia and thrombocytopenia. Of the reported families with IPEX, most affected boys died before the age of 3 years of malabsorbtion, failure to thrive, infections, or other complications. Characteristic findings at autopsy include lymphocytic infiltrates affecting the lungs, endocrine organs, such as pancreas and thyroid and skin, and increased lymphoid elements in lymph nodes and spleen. Although symptomatic therapy with immunosuppressive drugs provides some beneficial effects, the only curative treatment is hematopoietic stem cell transplantation.

Immunodeficiencies with Autoimmune Consequences

Far from being mutually exclusive, immunodeficiency and autoimmunity may occur simultaneously. During the last years, analysis of Autoimmune Polyendocrinopathy--Candidiasis--Ectodermal Dystrophy (APECED) and Immunodysregulation--Polyendocrinopathy--Enteropathy--X-linked (IPEX), two rare monogenic forms of immunodeficiency associated with autoimmunity, has led to the identification of Auto Immune Regulator (AIRE) and Forkhead Box P3 (FOXP3), essential transcriptional regulators, involved in central tolerance and peripheral immune homeostasis, respectively. Characterization of the molecular and cellular mechanisms involved in APECED, and recognition that AIRE expression is sustained by effective thymopoiesis, has recently allowed to define that the autoimmunity of Omenn syndrome, a combined immunodeficiency due to defects of V(D)J recombination, also results from defective expression of AIRE. The implications of identification of the basis of autoimmunity in these rare forms of immunodeficiency have important implications for a better understanding of more common autoimmune disorders, and for development of novel therapeutic approaches.

FOXP3 acts as a rheostat of the immune response

The study of a rare human X-linked disease resulting in a characteristic clinical phenotype of multiple autoimmune disorders and the in-depth exploration of a spontaneous mouse model, scurfy (sf), have contributed to a better understanding of the regulation of immunologic responses, particularly to self. Forkhead box P3 (FOXP3), the gene responsible for IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) and sf is located on the X chromosome and is of crucial importance for the generation of CD4+ CD25+ regulatory T cells. Loss of FOXP3 function and the resultant lack of regulatory T cells result in lethal auto-aggressive lymphoproliferation, whereas overexpression of this modulator results in severe immunodeficiency. The in-depth analysis of FOXP3 regulation and elucidation of the precise mechanisms by which FOXP3 exerts its regulatory effect will provide important insights into the understanding of autoimmunity and should predictably result in new therapeutic possibilities.

Infantile hyperinsulinism associated with enteropathy, deafness and renal tubulopathy: clinical manifestations of a syndrome caused by a contiguous gene deletion located on chromosome 11p

We describe the clinical features of a new syndrome causing hyperinsulinism in infancy (HI), severe enteropathy, profound sensorineural deafness, and renal tubulopathy in three children born to two pairs of consanguineous parents. This combination of clinical features is explained by a 122-kb contiguous gene deletion on the short arm of chromosome 11. It deletes 22 of the 39 exons of the gene coding for the SUR1 component of the KATP channel on the pancreatic beta-cell thereby causing severe HI. It also deletes all but two of the 28 exons of the USH1C gene, which causes Usher syndrome and is important for the normal development and function of the ear and the eye, the gastrointestinal tract, and the kidney, thereby accounting for the symptoms of deafness, vestibular dysfunction and retinal dystrophy seen in type 1 Usher syndrome, diarrhoea, malabsorption, and tubulopathy. This contiguous gene deletion provides important insights into the normal development of several body organ systems.

Autoimmune enteropathy: molecular concepts

PURPOSE OF REVIEW

Enteropathies causing temporary or permanent intestinal failure are a big diagnostic and therapeutic challenge for pediatric gastroenterologists. A now well-recognized and distinct entity is in the form of "autoimmune enteropathy (AIE)". Recent advances in the molecular workup of AIE gave first insight into the pathophysiology of AIE. In this review, we discuss new molecular concepts of AIE resulting in new diagnostic and therapeutic possibilities.

RECENT FINDINGS

The identification of disease-causing mutations in the FOXP3 gene as a basic defect resulting in AIE points to a defect in regulatory T-cell homeostasis. FOXP3, primarily expressed by CD4+CD25+regulatory T cells, is a potent transcriptional suppressor and key modulator of T-cell functions. Nonfunctional FOXP3 leads to a tremendous hyperactivation of T cells, resulting in autoimmune aggression, such as seen in patients with immune dysregulation, polyendocrinopathy autoimmune enteropathy X-linked (IPEX) syndrome, a subgroup of AIE. There is recent evidence suggesting that a defect of regulatory factors other than FOXP3 might cause AIE. Anti-enterocyte autoantibodies, another main characteristic of AIE, seem to be of a secondary nature and can no more be considered as directly disease causing.

SUMMARY

Based on the profound immune dysregulation, new treatment strategies emerged for AIE. The use of T-cell immunosuppressive drugs, such as tacrolimus combined to steroids, seems to be beneficial in some patients; however, long-term remission is not always possible. Bone marrow transplantation might be the treatment of choice in those patients who do not respond to immunosuppression; however, the first encouraging results remain to be confirmed since to date long-term outcome remains mixed.

Clinical and immunological features of adult-onset generalized autoimmune gut disorder

OBJECTIVES

Autoimmune enteropathy is a rare disorder of unknown pathogenesis, characterized by protracted diarrhea, villous atrophy, and enterocyte autoantibodies. Its association with extended inflammation of the whole gastrointestinal tract is termed as generalized autoimmune gut disorder (GAGD), generally a pediatric disease of difficult management due to its association with immunodeficiency. The aim of our work is to describe the mucosal immunological basis of an adult-onset case of GAGD.

METHODS

We studied an adult female with a severe inflammatory involvement of the gastrointestinal tract (stomach, small and large bowel, and liver) and antienterocyte autoantibodies. She had antibody deficiency and a predisposition to systemic autoimmunity. We analyzed, by immunohistochemistry and flow cytometry, the phenotypic and functional characteristics of her intestinal intraepithelial and lamina propria (LP) lymphocytes.

RESULTS

We observed the prominent and constant presence of an unusual CD4+alphaE/beta7- Tc subset in the jejunal epithelium. Signs of the lymphocyte activation as well as the prominent lymphoid TNF-alpha production observed in the rectal mucosa support the involvement of a cell-mediated pro-inflammatory response in the pathogenesis of GAGD.

CONCLUSIONS

We report the second case of an adult fulfilling all diagnostic criteria for GAGD. We propose that the activated LP CD4+ T lymphocytes, as well as those atypically located in the epithelium, may play a pathogenic role. The alphaE/beta7- IEL could constitute a diagnostic marker of intestinal autoimmunity in the cases when autoantibodies are not evidenced, and mucosal TNF-alpha might represent a novel therapeutic target in this severe disease.

Neonatal enteropathies: defining the causes of protracted diarrhea of infancy

The underlying causes of chronic diarrhea beginning early in life are increasingly well defined. Infectious and post-infectious enteropathies and food sensitive/allergic enteropathy account for the majority of cases. Recent attention has focused on characterizing defined entities, which cause protracted diarrhea in infants and young children. Disorders of intestinal ion transport usually present at birth following a pregnancy complicated by polyhydramnios. Intestinal mucosal biopsies show normal architect with intact villus-crypt axis. Neonatal enteropathies, by contrast, are characterized by blunting of the villi. These include microvillus inclusion disease, tufting enteropathy, autoimmune enteropathy and IPEX syndrome - and it is these conditions that are the subject of the current review.

Immune dysregulation, polyendocrinopathy, enteropathy, and X-linked inheritance (IPEX), a syndrome of systemic autoimmunity caused by mutations of FOXP3, a critical regulator of T-cell homeostasis

Immune dysregulation, polyendocrinopathy, enteropathy, and X-linked inheritance (IPEX) is one of a group of clinical syndromes that present with multisystem autoimmune disease suggesting a phenotype of immune dysregulation. Clinically, IPEX manifests most commonly with diarrhea, insulin-dependent diabetes mellitus, thyroid disorders, and eczema. FOXP3, the gene responsible for IPEX, maps to chromosome Xp11.23-Xq13.3 and encodes a putative DNA-binding protein of the forkhead family. Recent data indicate that FOXP3 is expressed primarily in the CD4+CD25+ regulatory T-cell subset, where it may function as a transcriptional repressor and key modulator of regulatory T-cell fate and function. This review describes the clinical features of IPEX and the structure, function, and known mutations of FOXP3 that provide important insights into its role in maintenance of immune homeostasis.

Clinical and molecular features of the immunodysregulation, polyendocrinopathy, enteropathy, X linked (IPEX) syndrome

Immunodysregulation, polyendocrinopathy, enteropathy, X linked (IPEX, OMIM 304790) is a rare, recessive disorder resulting in aggressive autoimmunity and early death. Mutations in FOXP3 have been identified in 13 of 14 patients tested. Research in the mouse model, scurfy, suggests that autoimmunity may stem from a lack of working regulatory T cells. We review published reports regarding the genetics, clinical features, immunology, pathology, and treatment of IPEX. We also report three new patients who were treated with long term immunosuppression, followed by bone marrow transplantation in two. IPEX can be differentiated from other genetic immune disorders by its genetics, clinical presentation, characteristic pattern of pathology, and, except for high IgE, absence of substantial laboratory evidence of immunodeficiency. While chronic treatment with immunosuppressive drugs may provide temporary benefit for some patients, it does not cause complete remission. Remission has been observed with bone marrow transplantation despite incomplete engraftment, but the long term outcome is uncertain.

Identification of an autoimmune enteropathy-related 75-kilodalton antigen

BACKGROUND & AIMS

We have previously reported a 75-kilodalton autoantigen specific to X-linked autoimmune enteropathy (AIE) associated with tubulonephropathy. The aim of this study was to identify the autoantigen.

METHODS

Complementary DNA (cDNA) clones were isolated by immunoscreening a human duodenal cDNA-expression library with serum from a patient with AIE.

RESULTS

cDNA encoding the 75-kilodalton antigen (AIE-75) was identified. The composite nucleotide sequence of the cDNA for AIE-75 was 2214 base pairs long and encoded 552 amino acids. The genomic sequence of AIE-75 was found in Sequence DataBank, which consisted of 21 exons and was located on the chromosome 11p14.3. Recombinant AIE-75 specifically reacted with sera from 3 of 4 unrelated patients with AIE but not with 58 control sera. AIE-75 was predominantly distributed in the epithelial cells of the luminal surface and the upper half of the crypts of the intestine and in the proximal renal tubulus. Similarity searches revealed that the AIE-75 cDNA sequence was an authentic form of several colon cancer-related cDNAs of unknown function. The deduced amino acid sequence contained 3 conserved PSD-95/Dlg/ZO-1 (PDZ) domains.

CONCLUSIONS

AIE-75 is a PDZ domain-containing protein expressed in the differentiated epithelial cells of the intestine and kidney and may be involved in protein-protein interaction. The identification of the autoantigen may prove useful in the approach to the pathogenesis of this poorly understood disease.