Autoimmunity in common variable immunodeficiency

Decoding mutational hotspots in human disease through the gene modules governing thymic regulatory T cells

Computational strategies to extract meaningful biological information from multiomics data are in great demand for effective clinical use, particularly in complex immune-mediated disorders. Regulatory T cells (Tregs) are essential for immune homeostasis and self-tolerance, controlling inflammatory and autoimmune processes in many diseases with a multigenic basis. Here, we quantify the Transcription Factor (TF) differential occupancy landscape to uncover the Gene Regulatory Modules governing lineage-committed Tregs in the human thymus, and show that it can be used as a tool to prioritise variants in complex diseases. We combined RNA-seq and ATAC-seq and generated a matrix of differential TF binding to genes differentially expressed in Tregs, in contrast to their counterpart conventional CD4 single-positive thymocytes. The gene loci of both established and novel genetic interactions uncovered by the Gene Regulatory Modules were significantly enriched in rare variants carried by patients with common variable immunodeficiency, here used as a model of polygenic-based disease with severe inflammatory and autoimmune manifestations. The Gene Regulatory Modules controlling the Treg signature can, therefore, be a valuable resource for variant classification, and to uncover new therapeutic targets. Overall, our strategy can also be applied in other biological processes of interest to decipher mutational hotspots in individual genomes.

Assessment of autoantibodies in paediatric population with primary immunodeficiencies: a pilot study

BACKGROUND

The correlation between primary immunodeficiencies (PIDs) and autoimmunity shows ethnic and geographical diversity. The aim of our study was to accumulate more data in paediatric PID population.

METHODS

58 children aged 1-17 and with PID (study group) and 14 age-matched immunocompetent individuals (control group) were included in the study. Serum levels of 17 different specific IgG antibodies against autoantigens were measured by means of a quantitative enzyme immunoassay. Immunoglobulin levels were analysed in relation to a detailed medical examination.

RESULTS

Autoantibodies against one or more antigens were detected in the sera of 24.14% (n = 14) subjects in the study group. The most frequent were anti-thyroid peroxidase (anti-TPO) antibodies (n = 8; 13.8%). Anti-TPO antibody levels were elevated more often in PID patients with a positive family history of autoimmune diseases (p = 0.04). The screening for anti-deamidated gliadin peptide (DGP) and anti-tissue transglutaminase (tTG) antibodies in our series allowed identifying two previously undiagnosed cases of coeliac disease in PID patients. There was no statistically significant difference between the study and the control group in terms of the autoantibodies prevalence.

CONCLUSIONS

This study provides data on the prevalence of autoantibodies in paediatric population diagnosed with PID. Selected autoantibodies (i.e. anti-tTG, anti-DGP) might be useful for the screening of PID to avoid the delay of diagnosis of an autoimmune disease.

The Dysfunctional Immune System in Common Variable Immunodeficiency Increases the Susceptibility to Gastric Cancer

Gastric carcinoma (GC) represents the most common cause of death in patients with common variable immunodeficiency (CVID). However, a limited number of cases have been characterised so far. In this study, we analysed the clinical features, bacterial/viral infections, detailed morphology and immune microenvironment of nine CVID patients with GC. The study of the immune microenvironment included automated digital counts of CD20+, CD4+, CD8+, FOXP3+, GATA3+ and CD138+ immune cells, as well as the evaluation of PD-L1 expression. Twenty-one GCs from non-CVID patients were used as a control group. GC in CVID patients was diagnosed mostly at early-stage (n = 6/9; 66.7%) and at younger age (median-age: 43y), when compared to non-CVID patients (p < 0.001). GC pathogenesis was closely related to Helicobacter pylori infection (n = 8/9; 88.9%), but not to Epstein-Barr virus (0.0%) or cytomegalovirus infection (0.0%). Non-neoplastic mucosa (non-NM) in CVID-patients displayed prominent lymphocytic gastritis (100%) and a dysfunctional immune microenvironment, characterised by higher rates of CD4+/CD8+/Foxp3+/GATA3+/PD-L1+ immune cells and the expected paucity of CD20+ B-lymphocytes and CD138+ plasma cells, when compared to non-CVID patients (p < 0.05). Changes in the immune microenvironment between non-NM and GC were not equivalent in CVID and non-CVID patients, reflecting the relevance of immune dysfunction for gastric carcinogenesis and GC progression in the CVID population.

Neutropenia in Patients with Common Variable Immunodeficiency: a Rare Event Associated with Severe Outcome

BACKGROUND

Common variable immunodeficiency (CVID) is characterized by infections and hypogammaglobulinemia. Neutropenia is rare during CVID.

METHODS

The French DEFI study enrolled patients with primary hypogammaglobulinemia. Patients with CVID and neutropenia were retrospectively analyzed.

RESULTS

Among 473 patients with CVID, 16 patients displayed neutropenia (lowest count [0-1400]*10⁶/L). Sex ratio (M/F) was 10/6. Five patients died during the follow-up (11 years) with an increased percentage of deaths compared to the whole DEFI group (31.3 vs 3.4%, P < 0.05). Neutropenia was diagnosed for 10 patients before 22 years old. The most frequent symptoms, except infections, were autoimmune cytopenia, i.e., thrombopenia or anemia (11/16). Ten patients were affected with lymphoproliferative diseases. Two patients were in the infection only group and the others belonged to one or several other CVID groups. The median level of IgG was 2.6 g/L [0.35-4.4]. Most patients presented increased numbers of CD21^low CD38^low B cell, as already described in CVID autoimmune cytopenia group. Neutropenia was considered autoimmune in 11 cases. NGS for 52 genes of interest was performed on 8 patients. No deleterious mutations were found in LRBA, CTLA4, and PIK3. More than one potentially damaging variant in other genes associated with CVID were present in most patients arguing for a multigene process.

CONCLUSION

Neutropenia is generally associated with another cytopenia and presumably of autoimmune origin during CVID. In the DEFI study, neutropenia is coupled with more severe clinical outcomes. It appears as an "alarm bell" considering patients' presentation and the high rate of deaths. Whole exome sequencing diagnosis should improve management.

IL-10-Producing Regulatory B Cells Are Decreased in Patients with Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is the most prevalent symptomatic primary immunodeficiency in adults. CVID patients often present changes in the frequency and function of B lymphocytes, reduced number of Treg cells, chronic immune activation, recurrent infections, high incidence of autoimmunity and increased risk for malignancies. We hypothesized that the frequency of B10 cells would be diminished in CVID patients because these cells play an important role in the development of Treg cells and in the control of T cell activation and autoimmunity. Therefore, we evaluated the frequency of B10 cells in CVID patients and correlated it with different clinical and immunological characteristics of this disease. Forty-two CVID patients and 17 healthy controls were recruited for this study. Cryopreserved PBMCs were used for analysis of T cell activation, frequency of Treg cells and characterization of B10 cells by flow cytometry. IL-10 production by sorted B cells culture and plasma sCD14 were determined by ELISA. We found that CVID patients presented decreased frequency of IL-10-producing CD24^hiCD38^hi B cells in different cell culture conditions and decreased frequency of IL-10-producing CD24^hiCD27⁺ B cells stimulated with CpG+PIB. Moreover, we found that CVID patients presented lower secretion of IL-10 by sorting-purified B cells when compared to healthy controls. The frequency of B10 cells had no correlation with autoimmunity, immune activation and Treg cells in CVID patients. This work suggests that CVID patients have a compromised regulatory B cell compartment which is not correlated with clinical and immunological characteristics presented by these individuals.

Clinical Features, Non-Infectious Manifestations and Survival Analysis of 161 Children with Primary Immunodeficiency in Mexico: A Single Center Experience Over two Decades

PURPOSE

The hallmark of Primary immunodeficiencies (PID) is unusual infection, although other immunological non-infectious manifestations such as autoimmunity, allergy and cancer are often present. Most published reports focus on one disease or defect groups, so that a global prevalence of non-infectious manifestations of PID is hard to find. We aimed to describe the clinical features of our pediatric patients with PID, as well as the frequency and evolution of allergy, cancer and autoimmunity.

METHODS

We reviewed all the available charts of patients being followed for PID from 1991 to the spring of 2012 at the National Institute of Pediatrics, Mexico City, to describe their demographic, clinical and laboratory features. Their diagnoses were established by pediatric immunologists in accordance to ESID criteria, including routine immunological workup and specialized diagnostic assays. We divided patients by decade of diagnosis to analyze their survival curves.

RESULTS

There were 168 charts available, from which we excluded one duplicate and six equivocal diagnoses. We studied the charts of 161 PID patients (68% male, 86% alive), mostly from the center of the country, with a positive family history in 27% and known consanguinity in 11%. Eighty percent of the patients were diagnosed during the last decade. Current median age was 124 months; median age at onset of infections, 12 months; median age at diagnosis, 52 months; median age at death, 67.5 months. Severe infection and bleeding were the cause of 22 deaths. Eighty-six percent of all patients had at least one infection, while non-infectious manifestations had a global prevalence of 36%, namely: autoimmunity 19%, allergies 17%, and cancer 2.4%. Survival curves were not significantly different when compared by decade of diagnosis.

CONCLUSIONS

Compared to other registry reports, we found a lower prevalence of antibody defects, and of associated allergy and cancer. We could only locate two isolated IgA deficiencies and four cases of cancer among our PID patients. Although antibody defects are the most prevalent group (30%), the distribution we found is similar to that reported in Iran, Kuwait, Egypt and Taiwan, with a close 27% share for phagocyte defects, and 26% for the formerly called "well-defined" syndromes. Of note, autoimmune and inflammatory complications are high among our patients with chronic granulomatous disease, as has been reported in both the United States and Japan, but not in Europe.

Genetic defects and the role of helper T-cells in the pathogenesis of common variable immunodeficiency

Common variable immunodeficfiiency (CVID) is a primary immunodeficiency syndrome representing a heterogeneous set of disorders resulting mostly in antibody deficiency and recurrent infections. However, inflammatory and autoimmune disorders and some kinds of malignancies are frequently reported as a part of the syndrome. Although it is one of the most widespread primary immunodeficiency, only recently some genetic defects in CVID have been identified. Mutations have been detected in inducible T-cell costimulator (ICOS), transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), B-cell activating factor-receptor (BAFF-R), B-cell receptor complex (CD19, CD21 and CD81) and CD20. On the other hand, recent studies have shown a decrease in T-helper-17 cells frequency and their characteristic cytokines in CVID patients and this emphasis on the vital role of the T-cells in immunopathogenesis of the CVID. Furthermore, in the context of autoimmune diseases accompanying CVID, interleukin 9 has recently attracted a plenty of considerations. However, the list of defects is expanding as exact immunologic pathways and genetic disorders in CVID are not yet defined. In this review, we have a special focus on the immunopathogenesis of CVID, recent advances in understanding the underlying etiology and genetics for patients.

Common variable immunodeficiency

Common variable immunodeficiency (CVID) is a common primary immunodeficiency characterized by a failure in B-cell differentiation with defective immunoglobulin production. Affected patients are uniquely susceptible to recurrent infection with encapsulated organisms and have an increased propensity for the development of inflammatory and autoimmune manifestations. The diagnosis of CVID is commonly delayed and the underlying cause of the disorder is not understood. Replacement antibody therapy reduces the risk of serious infections. However, optimal treatment regimens for the uncommon manifestations associated with this disease, such as granulomatous lymphocytic interstitial lung disease, require further research.

Autoimmunity in immunodeficiency

Primary immunodeficiencies (PID) comprise a diverse group of clinical disorders with varied genetic defects. Paradoxically, a substantial proportion of PID patients develop autoimmune phenomena in addition to having increased susceptibility to infections from their impaired immunity. Although much of our understanding comes from data gathered through experimental models, there are several well-characterized PID that have improved our knowledge of the pathways that drive autoimmunity. The goals of this review will be to discuss these immunodeficiencies and to review the literature with respect to the proposed mechanisms for autoimmunity within each put forth to date.

Evaluation of CD4+CD25+FOXP3+ regulatory T cells function in patients with common variable immunodeficiency

Common variable immunodeficiency (CVID) is one of the predominant antibody disorders where abnormalities in regulatory T cells (Tregs) may result in autoimmunity and chronic inflammation. To evaluate Tegs frequency and function, 13 CVID patients and 10 age- and sex-matched healthy volunteer were enrolled. The percentages of Tregs were calculated using flow cytomety method. For assessment of Treg function, Tregs were isolated and their suppressive functions were determined using Tregs suppression assay. The levels of immunoregulatory cytokines IL-10 and TGF-β produced by Tregs were also measured. Our results revealed that Tregs frequency (P<0.001) and their suppressive functions (P<0.001) were impaired in CVID patients. The level of TGF-β did not differ between CVID patients and controls (p=0.09); while the amount of IL-10 was remarkably decreased in CVID patients (P=0.007). Our findings suggest that disturbed Tregs frequency and their functional characteristics might account for aberrant immune responses observed in CVID patients.

Epigenetics, autoimmunity and hematologic malignancies: a comprehensive review

The relationships between immunological dysfunction, loss of tolerance and hematologic malignancies have been a focus of attention in attempts to understand the appearance of a higher degree of autoimmune disease and lymphoma in children with congenital immunodeficiency. Although multiple hypotheses have been offered, it is clear that stochastic processes play an important role in the immunopathology of these issues. In particular, accumulating evidence is defining a role of epigenetic mechanisms as being critical in this continuous spectrum between autoimmunity and lymphoma. In this review, we focus attention predominantly on the relationships between T helper 17 (Th17) and T regulatory populations that alter local microenvironments and ultimately the expression or transcription factors involved in cell activation and differentiation. Abnormal expression in any of the molecules involved in Th17 and/or Treg development alter immune homeostasis and in genetically susceptible hosts may lead to the appearance of autoimmunity and/or lymphoma. These observations have clinical significance in explaining the discordance of autoimmunity in identical twins. They are also particularly important in the relationships between primary immune deficiency syndromes, immune dysregulation and an increased risk of lymphoma. Indeed, defining the factors that determine epigenetic alterations and their relationships to immune homeostasis will be a challenge greater or even equal to the human genome project.

[Primary immunodeficiencies presenting with autoimmune cytopenias in adults]

Although primary immunodeficiencies (PID) are typically marked by increased susceptibility to infections, autoimmune manifestations have increasingly been recognized as an important component of several forms of PID. Here, we discuss two forms of PID in which autoimmune cytopenias are particularly common and may be the first manifestation of the disease in adults: autoimmune lymphoproliferative syndrome (ALPS) and common variable immunodeficiency (CVID). Approximately one fifth of patients with CVID develop autoimmune diseases, and immune thrombocytopenic purpura (ITP) and autoimmune hemolytic anemia (AHA) are the most common. Since autoimmune cytopenias frequently precede the diagnosis of CVID, testing for immunoglobulin levels should be performed in patients diagnosed with AITP and AHA. Patients with CVID in association with autoimmune cytopenias have a "particular phenotype" with lower susceptibility to infection and higher susceptibility to autoimmune manifestations and, for patients with AHA, a more frequent development of splenomegaly and lymphoma. Corticosteroids and high doses of intravenous immunoglobulins (IVIg) seem to have the same efficacy as in idiopathic AITP and AHA. Splenectomy and rituximab are as effective as in idiopathic autoimmune cytopenias but are associated with an increased risk of severe infection and should, in our opinion, be considered only for those rare patients with "refractory diseases". The course and outcome of autoimmune cytopenias is not affected by supportive IVIg therapy. Autoimmune destruction of blood cells affects over 70% of ALPS patients. The median age of first presentation is 24 months of age, but with increasing awareness of this condition, adults with autoimmune cytopenias are now being diagnosed more frequently. Testing for ALPS should therefore be considered in young adults with unexplained Evan's syndrome. Patients usually respond to immunosuppressive medications, including corticosteroids. Unlike many patients with idiopathic autoimmune cytopenias, the cytopenias in patients with ALPS typically do not respond to IVIg. After corticosteroids, the immunosuppressive drug that is the most studied in ALPS patients is mycophenolate mofetyl. Rituximab and splenectomy are relatively contraindicated in ALPS because of an increase risk of severe infection and should be reserved for patients who fail all other therapies.

Chronic inflammatory demyelinating polyneuropathy in common variable immunodeficiency

Common variable immunodeficiency comprises a heterogeneous group of primary antibody deficiencies with complex clinical and immunologic phenotypes. Immune dysregulation leads to the generation of multiple autoantibodies against various antigenic targets in patients with common variable immunodeficiency. Chronic inflammatory demyelinating polyneuropathy is a heterogeneous disorder that indicates an autoimmune response against peripheral nerve myelin. We describe a 7-year-old girl with common variable immunodeficiency who developed chronic inflammatory polyneuropathy. A 5-day course of intravenous immunoglobulin (500 mg/kg/day) improved her neurologic disorder. Chronic inflammatory demyelinating polyneuropathy should be added to the broadening spectrum of neurologic complications in common variable immunodeficiency. Early detection and consequent treatment may reverse the neurologic sequelae.

Primary B-cell deficiencies reveal a link between human IL-17-producing CD4 T-cell homeostasis and B-cell differentiation

IL-17 is a pro-inflammatory cytokine implicated in autoimmune and inflammatory conditions. The development/survival of IL-17-producing CD4 T cells (Th17) share critical cues with B-cell differentiation and the circulating follicular T helper subset was recently shown to be enriched in Th17 cells able to help B-cell differentiation. We investigated a putative link between Th17-cell homeostasis and B cells by studying the Th17-cell compartment in primary B-cell immunodeficiencies. Common Variable Immunodeficiency Disorders (CVID), defined by defects in B-cell differentiation into plasma and memory B cells, are frequently associated with autoimmune and inflammatory manifestations but we found no relationship between these and Th17-cell frequency. In fact, CVID patients showed a decrease in Th17-cell frequency in parallel with the expansion of activated non-differentiated B cells (CD21(low)CD38(low)). Moreover, Congenital Agammaglobulinemia patients, lacking B cells due to impaired early B-cell development, had a severe reduction of circulating Th17 cells. Finally, we found a direct correlation in healthy individuals between circulating Th17-cell frequency and both switched-memory B cells and serum BAFF levels, a crucial cytokine for B-cell survival. Overall, our data support a relationship between Th17-cell homeostasis and B-cell maturation, with implications for the understanding of the pathogenesis of inflammatory/autoimmune diseases and the physiology of B-cell depleting therapies.

Primary immunodeficiency and autoimmunity: lessons from human diseases

Primary immunodeficiency diseases (PID) are a genetically heterogenous group of >150 disorders that affect distinct components of the innate and adaptive immune system and are often associated with autoimmune diseases. We describe PID affecting T-regulatory cells, complement and B cells or their products and discuss the possibility of a cause-effect relationship. The high concordance of T-regulatory cell defects to organ-specific autoimmune disease implies an obligatory role of these cells in maintaining tolerance to epithelial and endocrine tissues; the absence of central nervous system involvement may reflect immunological privilege. Congenital defects in C1q, C1r/s and C4 are strongly associated with systemic lupus erythematosus (SLE), and this pattern along with laboratory evidence suggests a major importance of classical pathway activity in safe elimination of immune complexes and prevention of immune complex disease (ICD). It is debatable whether this ICD is to be regarded as an autoimmune disease (resulting from a breakdown of immunological ignorance to antigens that are normally hidden), as autoantibodies may be absent, and tissue damage because of deposition of immune complexes could account for all of the pathology observed. Evidence for a causative link between primary antibody deficiencies and autoimmune disease is much less compelling and may in fact involve a common genetic background. However, arguments have also been made in favour of the notion that an intense antigen load as a result of recurrent or persistent infections may affect either tolerance or ignorance, e.g. by molecular mimicry or the presence of superantigens. Similar immunological mechanisms might account for the vast majority of autoimmune diseases.

CD81 gene defect in humans disrupts CD19 complex formation and leads to antibody deficiency

Antibody deficiencies constitute the largest group of symptomatic primary immunodeficiency diseases. In several patients, mutations in CD19 have been found to underlie disease, demonstrating the critical role for the protein encoded by this gene in antibody responses; CD19 functions in a complex with CD21, CD81, and CD225 to signal with the B cell receptor upon antigen recognition. We report here a patient with severe nephropathy and profound hypogammaglobulinemia. The immunodeficiency was characterized by decreased memory B cell numbers, impaired specific antibody responses, and an absence of CD19 expression on B cells. The patient had normal CD19 alleles but carried a homozygous CD81 mutation resulting in a complete lack of CD81 expression on blood leukocytes. Retroviral transduction and glycosylation experiments on EBV-transformed B cells from the patient revealed that CD19 membrane expression critically depended on CD81. Similar to CD19-deficient patients, CD81-deficient patients had B cells that showed impaired activation upon stimulation via the B cell antigen receptor but no overt T cell subset or function defects. In this study, we present what we believe to be the first antibody deficiency syndrome caused by a mutation in the CD81 gene and consequent disruption of the CD19 complex on B cells. These findings may contribute to unraveling the genetic basis of antibody deficiency syndromes and the nonredundant functions of CD81 in humans.

Common variable immunodeficiency associated with inflammatory bowel disease and type I diabetes

Common variable immunodeficiency (CVID) is a heterogeneous group of primary immunodeficiency disorders characterized by defective antibody production, low levels of serum immunoglobulins and increased susceptibility to infection. The patient was a 39-year-old male who was admitted to the gastroenterology department with a two week history of diarrhea, blunt abdominal pain below the umbilicus, prolonged febrile state, loss of appetite and loss of body weight of 18 kg during the previous six months. Screening tests of serum immunoglobulins showed decreased concentrations of three types of immunoglobulins: IgA < 0.24 g/L, IgM < 0.18 g/L and IgG < 1.55 g/L. Lymphocytes immunophenotypisation revealed inversed CD4⁺/8⁺ T cells ratio, 0.31 and absence of plasma cells (CD138 negative). Colonoscopy showed a rectal mucosa like cobblestones with multiple longitudinal and serpentinous ulceration, without involvement of other segments of the colon and the small intestine. Histopathology revealed aphtous ulcerative lesions, transmural inflammation with multiple lymphoid aggregates and benign lymphoid nodular hyperplasia of the small intestine. Plasma cells were absent from the lamina propria. Magnetic resonance imaging of a perianal fistula demonstrated a trans-sphicteric type. This case is specific because of the three illnesses associated and only one case of an association of diabetes mellitus type I and immunodeficiency reported thus far.

A decreased frequency of regulatory T cells in patients with common variable immunodeficiency

Introduction

Common variable immunodeficiency disorder (CVID) is a heterogeneous syndrome, characterized by deficient antibody production and recurrent bacterial infections in addition abnormalities in T cells. CD4⁺CD25^high regulatory T cells (Treg) are essential modulators of immune responses, including down-modulation of immune response to pathogens, allergens, cancer cells and self-antigens.

Objective

In this study we set out to investigate the frequency of Treg cells in CVID patients and correlate with their immune activation status.

Materials and Methods

Sixteen patients (6 males and 10 females) with CVID who had been treated with regular intravenous immunoglobulin and 14 controls were enrolled. Quantitative analyses of peripheral blood mononuclear cells (PBMC) were performed by multiparametric flow cytometry using the following cell markers: CD38, HLA-DR, CCR5 (immune activation); CD4, CD25, FOXP3, CD127, and OX40 (Treg cells); Ki-67 and IFN-γ (intracellular cytokine).

Results

A significantly lower proportion of CD4⁺CD25^highFOXP3 T cells was observed in CVID patients compared with healthy controls (P<0.05). In addition to a higher proportion of CD8⁺ T cells from CVID patients expressing the activation markers, CD38⁺ and HLA-DR⁺ (P<0.05), we observed no significant correlation between Tregs and immune activation.

Conclusion

Our results demonstrate that a reduction in Treg cells could have impaired immune function in CVID patients.

Common variable immunodeficiency (CVID): case report and review of the literature

Common variable immunodeficiency (CVID) is an immunodeficiency disease characterized by diminished ability to produce immunoglobulins. CVID has an estimated incidence of 1:10,000 to 1:200,000 (male:female 1:1) and usually presents in the second and third decade, although it also has a peak of incidence in childhood. The exact pathophysiology remains unclear. CVID can be associated with autoimmune, granulomatous and gastrointestinal diseases and patients have a predisposition to malignancies (especially non-Hodgkin lymphoma). Since different organ systems can be affected, all clinicians need to be aware of this entity, especially when confronted with patients with recurrent infections and/or multiple autoimmune diseases.

Common variable immunodeficiency

Common variable immunodeficiency is the most prevalent clinically significant antibody deficiency at all ages. The disorder is defined principally by characteristic infection susceptibility with hypogammaglobulinemia and impaired-specific antibody response. Several recent large registry-based studies have defined distinct phenotypic subtypes. Several studies have also correlated specific immunologic markers with these phenotypes. The biochemical or genetic abnormality in the majority of patients remains unknown. Recently, several molecular genetic lesions have been defined. Among these, mutations of inducible costimulator, and CD19, appear to be disease causing by themselves. These account for about 1% of cases. Other mutations or polymorphisms, such as in the human homolog of Escherichia coli MutS 5 (MSH5), and transmembrane activator and calcium mobilizing ligand interactor, seem to be disease associated in 5-10% of patients, but may require additional immunologic abnormalities for full expression of the phenotype, as unaffected heterozygotes have also been described.

Intrinsic defect of the immune system in children with Down syndrome: a review

Down syndrome (DS) is the most frequent cause of mental retardation in man. Immunological changes in DS have been observed since the 1970s. The neurological system appears to be ageing precociously, with early occurrence of Alzheimer disease; until now, the observed immunological differences have been interpreted in the same context. Looking back at past and present results of immunological studies in DS children in relation to the clinical consequences they suffer, we conclude that it is more likely that the DS immune system is intrinsically deficient from the very beginning.

Primary immunodeficiencies (PIDs) presenting with cytopenias

Autoimmune manifestations are increasingly being recognized as a component of several forms of primary immunodeficiencies (PID). Defects in purging of self-reactive T and B cells, impaired Fas-mediated apoptosis, abnormalities in development and/or function of regulatory T cells, and persistence of immune activation as a result of inability to clear infections have been shown to account for this association. Among autoimmune manifestations in patients with PID, cytopenias are particularly common. Up to 80% of patients with autoimmune lymphoproliferative syndrome (ALPS) have autoantibodies, and autoimmune hemolytic anemia and immune thrombocytopenia have been reported in 23% and 51% of ALPS patients, and may even mark the onset of the disease. ALPS-associated cytopenias are often refractory to conventional treatment and represent a therapeutic challenge. Autoimmune manifestations occur in 22% to 48% of patients with common variable immunodeficiencies (CVIDs), and are more frequent among CVID patients with splenomegaly and granulomatous disease. Finally, autoimmune cytopenias have been reported also in patients with combined immunodeficiency. In particular, autoimmune hemolytic anemia is very common among infants with nucleoside phosphorylase deficiency. While immune suppression may be beneficial in these cases, full resolution of the autoimmune manifestations ultimately depends on immune reconstitution, which is typically provided by hematopoietic cell transplantation.