Increased apoptosis of CD20+ IgA + B cells is the basis for IgA deficiency: the molecular mechanism for correction in vitro by IL-10 and CD40L

An overview of early genetic predictors of IgA deficiency

INTRODUCTION

Inborn errors of immunity (IEIs) refer to a heterogeneous category of diseases with defects in the number and/or function of components of the immune system. Immunoglobulin A (IgA) deficiency is the most prevalent IEI characterized by low serum level of IgA and normal serum levels of IgG and/or IgM. Most of the individuals with IgA deficiency are asymptomatic and are only identified through routine laboratory tests. Others may experience a wide range of clinical features including mucosal infections, allergies, and malignancies as the most important features. IgA deficiency is a multi-complex disease, and the exact pathogenesis of it is still unknown.

AREAS COVERED

This review compiles recent research on genetic and epigenetic factors that may contribute to the development of IgA deficiency. These factors include defects in B-cell development, IgA class switch recombination, synthesis, secretion, and the long-term survival of IgA switched memory B cells and plasma cells.

EXPERT OPINION

A better and more comprehensive understanding of the cellular pathways involved in IgA deficiency could lead to personalized surveillance and potentially curative strategies for affected patients, especially those with severe symptoms.

Intestinal Peyer's Patches: Structure, Function, and In Vitro Modeling

BACKGOUND

Considering the important role of the Peyer's patches (PPs) in gut immune balance, understanding of the detailed mechanisms that control and regulate the antigens in PPs can facilitate the development of immune therapeutic strategies against the gut inflammatory diseases.

METHODS

In this review, we summarize the unique structure and function of intestinal PPs and current technologies to establish in vitro intestinal PP system focusing on M cell within the follicle-associated epithelium and IgA⁺ B cell models for studying mucosal immune networks. Furthermore, multidisciplinary approaches to establish more physiologically relevant PP model were proposed.

RESULTS

PPs are surrounded by follicle-associated epithelium containing microfold (M) cells, which serve as special gateways for luminal antigen transport across the gut epithelium. The transported antigens are processed by immune cells within PPs and then, antigen-specific mucosal immune response or mucosal tolerance is initiated, depending on the response of underlying mucosal immune cells. So far, there is no high fidelity (patho)physiological model of PPs; however, there have been several efforts to recapitulate the key steps of mucosal immunity in PPs such as antigen transport through M cells and mucosal IgA responses.

CONCLUSION

Current in vitro PP models are not sufficient to recapitulate how mucosal immune system works in PPs. Advanced three-dimensional cell culture technologies would enable to recapitulate the function of PPs, and bridge the gap between animal models and human.

A novel method to standardise serum IgA measurements shows an increased prevalence of IgA deficiency in young children with recurrent respiratory tract infections

Objectives

While physicians are often confronted with immunoglobulin A (IgA) deficiency in children with recurrent infections, the clinical relevance of this finding is unclear. Large‐scale studies examining the significance of IgA deficiency in children are hampered by differences in techniques for measuring IgA and the physiological increase of IgA with age. Both result in a variety of reference values used for diagnosing IgA deficiency. We propose a new laboratory‐independent method to accurately compare IgA measurements in children of varying ages.

Methods

We present a method to standardise IgA values for age and laboratory differences. We applied this method to a multicentre case–control study of children under the age of seven suffering from recurrent respiratory tract infections (rRTI, cases) and children who had IgA measured as part of coeliac disease screening (controls). We defined IgA deficiency as serum IgA measurements < 2.5% for age‐specific reference values.

Results

We developed reference values for IgA for seven age groups and five different laboratory assays. Using these reference values, IgA measurements from 417 cases and 224 controls were standardised to compare groups. In children aged 2 years and older, IgA deficiency was observed in 2.9% (7/242) of cases and 0% (0/189) of controls (P = 0.02).

Conclusion

We present a method to compare IgA values in cohorts that vary in age and laboratory assay. This way, we showed that IgA deficiency was more prevalent in children with rRTI compared with controls. This implicates that IgA deficiency may be a clinically relevant condition, even in young children.

[Selective IgA deficiency]

Selective IgA deficiency (SIgAD) is defined by the European Society for Immunodeficiencies (ESID) as a serum IgA of less than 0.07g/L in patients greater than 4 years old with normal levels of IgG and IgM, normal vaccine responses, and with the exclusion of secondary causes of hypogammaglobulinemia. When serum IgA level is higher than 0.07g/L but two standard deviations below normal for age, the condition may be referred to as partial IgA deficiency, which is quite common. SIgAD is the most common primary immunodeficiency in Europe (1/600 in France) and most patients with SIgAD are asymptomatic (75-90%). The clinical complications associated with SIgAD include recurrent respiratory infections (in particular involving Haemophilus influenza and Streptococcus pneumoniae) and gastrointestinal (mainly due to Giardialamblia), autoimmune and allergic manifestations (anaphylaxis if blood products with IgA are administrated), inflammatory gastrointestinal disease. There is no specific treatment for SIgAD and each patient must be managed individually. While asymptomatic subjects do not need any treatment, it is still necessary for them to be up-to-date with vaccinations. If the patient experiences recurrent infections, prophylactic antibiotics may be beneficial. Immunoglobulin replacement therapy should be considered in patients with SIgAD and concomitant IgG subclass deficiency. Treatment for autoimmune and allergic manifestations is based on current standards of care for specific disease entities. To improve quality of life and reduce morbidity, an interdisciplinary team approach is essential.

Risk factors of partial IgA deficiency among low serum IgA patients: a retrospective observational study

Introduction

Partial IgA deficiency (pIgAD), including selective IgA deficiency, is one of the most common types of immunodeficiency. Early detection is crucial to prevent complications, such as recurrent infections and anaphylactic reactions to blood derivatives.

Material and methods

Useful screening methods have not yet been established. We conducted a single-center retrospective observational study, with low serum IgA patients to clarify the risk factors of pIgAD among patients with low serum levels of IgA. All patients with low serum IgA levels treated in our outpatient clinic from April 2010 to March 2016 were retrospectively reviewed using electronic medical records. We performed c² tests and Student’s t-tests for the univariate analysis, logistic regression analysis using the multiple imputation method for the multivariate analysis, and receiver operating characteristic (ROC) curve analysis.

Results

The univariate analysis showed statistically significant differences between the pIgAD group and the non-pIgAD group in age, gender, blood cell counts, serum protein levels, and renal function tests. The multivariate analysis revealed that female gender, a white blood cell counts lower than 10,000/µl, and a hemoglobin level of 10.0-15.0 g/dl are predictive factors of pIgAD.

Conclusions

After estimating any missing data using the multiple imputation method, age younger than 60 years old was also statistically significant. ROC curve analysis confirmed the validity of the model used in our multivariate analysis. When clinicians encounter low serum IgA patients who are female, of younger age, and have normal blood cell counts, and hemoglobin levels, they should suspect the existence of pIgAD.

IL-21 and anti-CD40 restore Bcl-2 family protein imbalance in vitro in low-survival CD27+ B cells from CVID patients

Common variable immunodeficiency (CVID) is characterized by an abnormal B cell differentiation to memory and antibody-secreting B cells. The defective functionality of CVID patients’ B cells could be the consequence of alterations in apoptosis regulation. We studied the balance of Bcl-2 family anti-/pro-apoptotic proteins to identify molecular mechanisms that could underlie B cell survival defects in CVID. We used flow cytometry to investigate Bcl-2, Bcl-XL, Bax, and Bim expression in B cells ex vivo and after anti-CD40 or anti-BCR activation with or without IL-21, besides to spontaneous and stimulation-induced Caspase-3 activation and viable/apoptotic B cell subpopulations. We found increased basal levels of Bax and Bim in CVID B cells that correlated with low viability and high Caspase-3 activation only in CD27⁺ B cells, particularly in a subgroup of apoptosis-prone CVID (AP-CVID) patients with low peripheral B cell counts and high autoimmunity prevalence (mostly cytopenias). We detected a broad B cell defect in CVID regarding Bcl-2 and Bcl-XL induction, irrespective of the stimulus used. Therefore, peripheral CVID memory B cells are prompted to die from apoptosis due to a constitutive Bcl-2 family protein imbalance and defective protection from activation-induced apoptosis. Interestingly, anti-CD40 and IL-21 induced normal and even higher levels of Bcl-XL, respectively, in CD27⁺ B cells from AP-CVID, which was accompanied by cell viability increase. Thus low-survival memory B cells from AP-CVID can overcome their cell death regulation defects through pro-survival signals provided by T cells. In conclusion, we identify apoptosis regulation defects as disease-contributing factors in CVID. B cell counts and case history of cytopenias might be useful to predict positive responses to therapeutic approaches targeting T-dependent signaling pathways.

Role of apoptosis in common variable immunodeficiency and selective immunoglobulin A deficiency

Common variable immunodeficiency (CVID) and selective IgA deficiency (SIgAD) are the most common primary immunodeficiencies in human. Both diseases share clinical manifestation and molecular defects. Increased apoptosis may be one of the mechanisms involved in the pathogenesis of CVID and SIgAD. Elevated apoptosis in this disorder leads to defective long-term survival of B-cells, reduced antibody production, decreased lymphocyte proliferation and defective cytokine secretion. For the first time, we reviewed the role of apoptosis in CVID and SIgAD.

CD27+ B cells from a subgroup of common variable immunodeficiency patients are less sensitive to apoptosis rescue regardless of interleukin-21 signalling

Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by hypogammaglobulinaemia and recurrent infections. Although the underlying cause is unknown, B cells from most CVID patients fail to differentiate to memory or plasma cells. We investigated if increased apoptosis could influence the fate of B cells. For this purpose we activated purified B lymphocytes of CVID patients with a surrogate T-dependent (anti-CD40) or T-independent [cytosine-phosphate-guanosine oligodeoxynucleotides (CpG-ODN) or anti-immunoglobulin (Ig)M)] stimulus with or without interleukin (IL)-21. We found that CD27(+) B cells were more sensitive than CD27(-) B cells to spontaneous apoptosis and less sensitive to rescue from apoptosis. The addition of IL-21 down-modulated the protective effect of all the stimuli on CD27(-) B cells and the protective effect of CpG-ODN and anti-IgM on CD27(+) B cells. In contrast, IL-21 rescued unstimulated CD27(-) B cells and improved the rescue of anti-CD40-stimulated CD27(+) B cells. When we compared patients and controls, mainly CD27(+) B cells from MB0 patients were less sensitive to rescue from apoptosis than those from MB1 patients and controls after activation, irrespective of the IL-21 effect. Increased apoptosis during an immune response could result in lower levels of immunoglobulin production in these patients.

[Clinical phenotypes associated with selective IgA deficiency: a review of 330 cases and a proposed follow-up protocol]

Selective IgA deficiency is the most common Primary Immune Deficiency. Only a small proportion of these patients present during childhood, but this proportion increases over the years, and may be associated with an IgG subclass deficiency with increased susceptibility to respiratory and digestive tract infections. During childhood, IgA deficient patients may also refer to symptoms related to allergic and autoimmune diseases or tumours.

AIMS

To describe the relationship of selective IgA deficiency with infections, allergic diseases, autoimmune disorders and tumours. To investigate the presence of other immune disorders associated with selective IgA deficiency. To suggest a follow-up protocol for these patients.

METHODS

Retrospective study of paediatric patients (<18 years) being followed-up in the Clinical Immunology Department between 1992 and 2007, as well as laboratory records with IgA values below 50mg/L. Clinical records were reviewed (frequency and intensity of diseases associated with selective IgA deficiency) along with immunology tests performed.

RESULTS

A total of 330 paediatric patients were identified with a selective IgA deficiency: 39 (11.8%) suffered from recurrent ear infections (2 developed secondary deafness), 58 (17.5%) from recurrent upper respiratory tract infections, and 20 patients (6%) from recurrent pneumonia, 6 of whom developed secondary bronchiectasis and 2 underwent a lobectomy. A relationship with atopic disease was found in 62 (18.78%) of patients. Regarding digestive disorders, chronic diarrhoea was found in 21 (6.5%), coeliac disease in 22 (6.6%), and persistently high plasma transaminases in 3. Autoimmune manifestations were found in 38 (11.5%), juvenile chronic arthritis, type 1 diabetes, vitiligo, cytopenia, and Crohn's disease, amongst others). Tumours were identified in 5 (1.5%). An IgG sub-class deficiency was found in 5 patients (4%), and 6 patients had a confirmed deficiency in antibody production.

CONCLUSIONS

In our cohort, 56.6% of patients with IgA deficiency showed other comorbidities which were, in decreasing frequency: recurrent infections (respiratory and ear infections), allergic diseases, autoimmunity and tumours. Some patients will develop a more severe humoral defect (IgG subclass deficiency with or without antibody deficiency).

Complexes between nuclear factor-κB p65 and signal transducer and activator of transcription 3 are key actors in inducing activation-induced cytidine deaminase expression and immunoglobulin A production in CD40L plus interleukin-10-treated human blood B cells

The signal transducer and activator of transcription 3 (STAT3) transcription factor pathway plays an important role in many biological phenomena. STAT3 transcription is triggered by cytokine-associated signals. Here, we use isolated human B cells to analyse the role of STAT3 in interleukin (IL)-10 induced terminal B cell differentiation and in immunoglobulin (Ig)A production as a characteristic readout of IL-10 signalling. We identified optimal conditions for inducing in-vitro IgA production by purified blood naive B cells using IL-10 and soluble CD40L. We show that soluble CD40L consistently induces the phosphorylation of nuclear factor (NF)-κB p65 but not of STAT3, while IL-10 induces the phosphorylation of STAT3 but not of NF-κB p65. Interestingly, while soluble CD40L and IL-10 were synergistic in driving the terminal maturation of B cells into IgA-producing plasma cells, they did not co-operate earlier in the pathway with regard to the transcription factors NF-κB p65 or STAT3. Blocking either NF-κB p65 or STAT3 profoundly altered the production of IgA and mRNA for activation-induced cytidine deaminase (AID), an enzyme strictly necessary for Ig heavy chain recombination. Finally, the STAT3 pathway was directly activated by IL-10, while IL-6, the main cytokine otherwise known for activating the STAT3 pathway, did not appear to be involved in IL-10-induced-STAT3 activation. Our results suggest that STAT3 and NF-κB pathways co-operate in IgA production, with soluble CD40L rapidly activating the NF-κB pathway, probably rendering STAT3 probably more reactive to IL-10 signalling. This novel role for STAT3 in B cell development reveals a potential therapeutic or vaccine target for eliciting IgA humoral responses at mucosal interfaces.

Interleukin-21 restores immunoglobulin production ex vivo in patients with common variable immunodeficiency and selective IgA deficiency

Interleukin-21 (IL-21) is an important promoter for differentiation of human B cells into immunoglobulin (Ig)–secreting cells. The objective of this study was to evaluate an IL-21–based approach to induce immunoglobulin production in B cells from patients with common variable immunodeficiency (CVID) or selective IgA deficiency (IgAD). We show that a combination of IL-21, IL-4, and anti-CD40 stimulation induces class-switch recombination to IgG and IgA and differentiation of Ig-secreting cells, consisting of both surface IgG+ (sIgG+) and sIgA+ B cells and CD138+ plasma cells, in patients with CVID or IgAD. Stimulation with IL-21 was far more effective than stimulation with IL-4 or IL-10. Moreover, spontaneous apoptosis of CD19+ B cells from patients with CVID or IgAD was prevented by a combination of IL-21, IL-4, and anti-CD40 stimulation. Analysis of IL-21 and IL-21 receptor (IL-21R) mRNA expression upon anti-CD3 stimulation of T cells, however, showed no evidence for defective IL-21 expression in CVID patients and sequencing of the coding regions of the IL21 gene did not reveal any mutations, suggesting a regulatory defect. Thus, our work provides an initial basis for a potential therapeutic role of IL-21 to reconstitute immunoglobulin production in CVID and IgAD.

B-lymphocyte stimulator and a proliferation-inducing ligand serum levels in IgA-deficient patients with and without celiac disease

IgA deficiency (IgAD) is the most common form of immunodeficiency and frequently associates with autoimmunity, especially with celiac disease (CD). The mechanisms underlying IgAD and the development of autoimmunity are still relatively unknown. Elevated B-lymphocyte stimulator (BLyS) and APRIL (a proliferation-inducing ligand) serum levels characterize several autoimmune diseases. We herein investigated BLyS and APRIL serum levels in IgAD patients with and without CD and compared these patients to CD patients with normal IgA and control patients (HBDs). Compared to HBDs, IgAD patients demonstrated a significant increase of BLyS (P < 0.0001) and APRIL (P = 0.003) levels, and no differences were seen between patients with or without CD. While BLyS appeared similarly overexpressed in IgAD and CD patients, APRIL was significantly increased only in IgAD patients. Because APRIL promotes IgA production, its overexpression may represent a physiological mechanism of compensation. BLyS upregulation may be involved in the increased risk of autoimmune disease development characterizing people carrying IgAD.

Various expression patterns of alpha1 and alpha2 genes in IgA deficiency

BACKGROUND

IgA deficiency (IgAD) is the most common immunodeficiency, however the pathogenesis in most cases of IgAD is unknown. There are 2 subclasses of IgA, IgA1 and IgA2, and its heavy chains are encoded by 2 different genes, the alpha1 and alpha2 genes. To investigate the molecular pathogenesis of IgA deficiency, it is important to evaluate each of the expressions of IgA1 and IgA2 separately.

METHODS

In this study, we report on the reverse transcriptase (RT)-PCR method in which alpha1 and alpha2 mRNAs can be separately evaluated. This method is based on electrophoretic separation using the difference of 39 bases between alpha1 and alpha2 mRNAs. Three selective, 5 partial and 2 secondary IgAD patients were examined.

RESULTS

In the 3 selective IgAD patients, no alpha1 or alpha2 mRNA expression was detected. In the 5 partial IgAD patients, various alpha1 and alpha2 mRNA expression patterns were found. One of the partial IgAD patients showed only alpha2 gene expression, but not alpha1 gene expression, and was found to show an alpha1 gene deletion together with gamma 2 and epsilon gene deletions. His plasma IgA2 level was within the normal range.

CONCLUSIONS

Patients with an alpha1 gene deletion can be considered as having partial IgAD. Using this method, we identified the second case of alpha1 gene deletion in Japan, and classified IgAD patients on the basis of alpha1 and alpha2 expression.

ICF, an immunodeficiency syndrome: DNA methyltransferase 3B involvement, chromosome anomalies, and gene dysregulation

The immunodeficiency, centromeric region instability, and facial anomalies syndrome (ICF) is the only disease known to result from a mutated DNA methyltransferase gene, namely, DNMT3B. Characteristic of this recessive disease are decreases in serum immunoglobulins despite the presence of B cells and, in the juxtacentromeric heterochromatin of chromosomes 1 and 16, chromatin decondensation, distinctive rearrangements, and satellite DNA hypomethylation. Although DNMT3B is involved in specific associations with histone deacetylases, HP1, other DNMTs, chromatin remodelling proteins, condensin, and other nuclear proteins, it is probably the partial loss of catalytic activity that is responsible for the disease. In microarray experiments and real-time RT-PCR assays, we observed significant differences in RNA levels from ICF vs. control lymphoblasts for pro- and anti-apoptotic genes (BCL2L10, CASP1, and PTPN13); nitrous oxide, carbon monoxide, NF-kappaB, and TNFalpha signalling pathway genes (PRKCH, GUCY1A3, GUCY1B3, MAPK13; HMOX1, and MAP4K4); and transcription control genes (NR2F2 and SMARCA2). This gene dysregulation could contribute to the immunodeficiency and other symptoms of ICF and might result from the limited losses of DNA methylation although ICF-related promoter hypomethylation was not observed for six of the above examined genes. We propose that hypomethylation of satellite 2 at 1qh and 16qh might provoke this dysregulation gene expression by trans effects from altered sequestration of transcription factors, changes in nuclear architecture, or expression of noncoding RNAs.

A flow cytometry technique to study intracellular signals NF-kappaB and STAT3 in peripheral blood mononuclear cells

Background

Cytokines have essential roles on intercellular communications and are effective in using a variety of intracellular pathways. Among this multitude of signalling pathways, the NF-κB (nuclear factor kappaB) and STAT (signal transducer and activator of transcription) families are among the most frequently investigated because of their importance. Indeed, they have important role in innate and adaptive immunity. Current techniques to study NF-κB and STAT rely on specific ELISAs, Western Blots and – most recently described – flow cytometry; so far, investigation of such signalling pathways are most commonly performed on homogeneous cells after purification.

Results

The present investigation aimed at developing a flow cytometry technique to study transcription factors in various cellular types such as mixtures of B-cells, T-lymphocytes and monocytes/macrophages stimulated in steady state conditions (in other words, as peripheral blood mononuclear cells). To achieve this goal, a two step procedure was carried out; the first one consisted of stimulating PBMCs with IL1β, sCD40L and/or IL10 in such a manner that optimal stimulus was found for each cell subset (and subsequent signal transduction, therefore screened by specific ELISA); the second step consisted of assessing confirmation and fine delineation of technical conditions by specific Western-Blotting for either NF-κB or STAT products. We then went on to sensitize the detection technique for mixed cells using 4 color flow cytometry.

Conclusion

In response to IL1β, or IL10, the levels of phosphorylated NF-κB and STAT3 – respectively – increased significantly for all the studied cell types. In contrast, B-cells and monocytes/macrophages – but, interestingly, not T-lymphocytes (in the context of PBMCs) – responded significantly to sCD40L by increasing phosphorylated NF-κB.

Management of a young patient with combined autoimmunity: Evans syndrome: a case report

Management of patients with autoimmune disease can present a challenge for clinicians. Combinations of autoimmune disorders carry a worse prognosis and are often difficult to diagnose. Evans syndrome is a rare hematologic disorder characterized by the concurrent presentation of autoimmune hemolytic anemia and immune thrombocytopenic purpura. This paper reports the first case of the dental management of a young patient with Evans, discusses the current literature surrounding the differential diagnosis and treatment of Evans syndrome, and suggests a guide for the oral medicine, pediatric dentist, or hospital dental clinician when treating these patients.

Incomplete penetrance of susceptibility genes for MHC-determined immunoglobulin deficiencies in monozygotic twins discordant for type 1 diabetes

Incomplete intrinsic penetrance is the failure of some genetically susceptible individuals (e.g., monozygotic twins of those who have a trait) to exhibit that trait. For the first time, we examine penetrance of susceptibility genes for multiple MHC gene-determined traits in the same subjects. Serum levels of IgA, IgD, IgG3, but not IgG4, in 50 pairs of monozygotic twins discordant for type 1 diabetes (T1D) correlated more closely in the twins than in random paired controls. The frequencies of subjects deficient in IgA (6%), IgD (33%) and IgG4 (12%), but not in IgG3, were higher in the twins than in controls. We postulate that this was because the MHC haplotypes (and possible non-MHC genes) that predispose to T1D also carry susceptibility genes for certain immunoglobulin deficiencies. Immunoglobulin deficiencies were not associated with T1D. Pairwise concordance for the deficiencies in the twins was 50% for IgA, 57% for IgD and 50% for IgG4. There were no significant associations among the specific immunoglobulin deficiencies except that all IgA-deficient subjects had IgD deficiency. Thus, intrinsic penetrance is a random process independently affecting different MHC susceptibility genes. Because multiple different external triggers would be required to explain the results, differential environmental determinants appear unlikely.