Molecular analysis of B-cell differentiation in selective or partial IgA deficiency

Genomic association and further characterisation of faecal immunoglobulin A deficiency in German Shepherd dogs

BACKGROUND

Immunoglobulin A (IgA) deficiency, chronic enteropathies and exocrine pancreatic insufficiency (EPI) have a high prevalence in German Shepherd dogs (GSD). This prospective study determined the prevalence of faecal IgA deficiency (IgAD) in GSD and investigated several candidate genes and the canine genome for a region or locus co-segregating with IgAD in GSD. Faecal IgA concentrations were quantified and genomic DNA was extracted from 8 GSD with an undetectable faecal IgA (classified as IgAD) and 80 non-IgAD GSD. The canine minimal screening set II microsatellite markers were genotyped, with evidence of an association at p < 1.0 × 10-3 . Faecal IgA concentrations were also tested for an association with patient clinical and biochemical variables.

RESULTS

Allele frequencies observed using the candidate gene approach were not associated with faecal IgAD in GSD. In the genome-wide association study (GWAS), the microsatellite marker FH2361 on canine chromosome 33 approached statistical significance for a link with IgAD in GSD (p = 1.2 × 10-3 ). A subsequent GWAS in 11 GSD with EPI and 80 control GSD revealed a significant association between EPI and FH2361 (p = 8.2 × 10-4 ).

CONCLUSIONS

The lack of an association with the phenotype of faecal IgAD in GSD using the candidate gene approach and GWAS might suggests that faecal IgAD in GSD is a relative or transient state of deficiency. However, the prevalence of faecal IgAD in GSD appears to be low (<3%). The relationship between faecal IgAD, EPI and loci close to FH2361 on canine chromosome 33 in GSD warrants further investigation.

Innate Mechanisms in Selective IgA Deficiency

Selective IgA deficiency (SIgAD), characterized by a serum IgA level below 0.07 mg/ml, while displaying normal serum levels of IgM and IgG antibodies, is the most frequently occurring primary immunodeficiency that reveals itself after the first four years after birth. These individuals with SIgAD are for the majority healthy and even when they are identified they are usually not investigated further or followed up. However, recent studies show that newborns and young infants already display clinical manifestations of this condition due to aberrancies in their immune defense. Interestingly, there is a huge heterogeneity in the clinical symptoms of the affected individuals. More than 50% of the affected individuals do not have clinical symptoms, while the individuals that do show clinical symptoms can suffer from mild to severe infections, allergies and autoimmune diseases. However, the reason for this heterogeneity in the manifestation of clinical symptoms of the individuals with SIgAD is unknown. Therefore, this review focusses on the characteristics of innate immune system driving T-cell independent IgA production and providing a mechanism underlying the development of SIgAD. Thereby, we focus on some important genes, including TNFRSF13B (encoding TACI), associated with SIgAD and the involvement of epigenetics, which will cover the methylation degree of TNFRSF13B, and environmental factors, including the gut microbiota, in the development of SIgAD. Currently, no specific treatment for SIgAD exists and novel therapeutic strategies could be developed based on the discussed information.

Primary Humoral Immune Deficiencies: Overlooked Mimickers of Chronic Immune-Mediated Gastrointestinal Diseases in Adults

In recent years, the incidence of immune-mediated gastrointestinal disorders, including celiac disease (CeD) and inflammatory bowel disease (IBD), is increasingly growing worldwide. This generates a need to elucidate the conditions that may compromise the diagnosis and treatment of such gastrointestinal disorders. It is well established that primary immunodeficiencies (PIDs) exhibit gastrointestinal manifestations and mimic other diseases, including CeD and IBD. PIDs are often considered pediatric ailments, whereas between 25 and 45% of PIDs are diagnosed in adults. The most common PIDs in adults are the selective immunoglobulin A deficiency (SIgAD) and the common variable immunodeficiency (CVID). A trend to autoimmunity occurs, while gastrointestinal disorders are common in both diseases. Besides, the occurrence of CeD and IBD in SIgAD/CVID patients is significantly higher than in the general population. However, some differences concerning diagnostics and management between enteropathy/colitis in PIDs, as compared to idiopathic forms of CeD/IBD, have been described. There is an ongoing discussion whether CeD and IBD in CVID patients should be considered a true CeD and IBD or just CeD-like and IBD-like diseases. This review addresses the current state of the art of the most common primary immunodeficiencies in adults and co-occurring CeD and IBD.

Defective formation of IgA memory B cells, Th1 and Th17 cells in symptomatic patients with selective IgA deficiency

Objective

Selective IgA deficiency (sIgAD) is the most common primary immunodeficiency in Western countries. Patients can suffer from recurrent infections and autoimmune diseases because of a largely unknown aetiology. To increase insights into the pathophysiology of the disease, we studied memory B and T cells and cytokine concentrations in peripheral blood.

Methods

We analysed 30 sIgAD patients (12 children, 18 adults) through detailed phenotyping of peripheral B‐cell, CD8⁺ T‐cell and CD4⁺ T‐cell subsets, sequence analysis of IGA and IGG transcripts, in vitro B‐cell activation and blood cytokine measurements.

Results

All patients had significantly decreased numbers of T‐cell‐dependent (TD; CD27⁺) and T‐cell‐independent (TI; CD27⁻) IgA memory B cells and increased CD21^low B‐cell numbers. IgM⁺IgD⁻ memory B cells were decreased in children and normal in adult patients. IGA and IGG transcripts contained normal SHM levels. In sIgAD children, IGA transcripts more frequently used IGA2 than controls (58.5% vs. 25.1%), but not in adult patients. B‐cell activation after in vitro stimulation was normal. However, adult sIgAD patients exhibited increased blood levels of TGF‐β1, BAFF and APRIL, whereas they had decreased Th1 and Th17 cell numbers.

Conclusion

Impaired IgA memory formation in sIgAD patients is not due to a B‐cell activation defect. Instead, decreased Th1 and Th17 cell numbers and high blood levels of BAFF, APRIL and TGF‐β1 might reflect disturbed regulation of IgA responses in vivo.

These insights into B‐cell extrinsic immune defects suggest the need for a broader immunological focus on genomics and functional analyses to unravel the pathogenesis of sIgAD.

Respiratory and allergic disorders in children with severe and partial immunoglobulin A immunodeficiency

BACKGROUND

Immunoglobulin A deficiency (IgAD) is the most common primary immunodeficiency. Although most people with selective IgAD (sIgAD) are asymptomatic, many patients often suffer from recurrent respiratory infections and different allergic disorders. Our aim was to investigate connection between subtypes of sIgAD and incidence of respiratory and allergic disorders, as well as connection with lung function changes in children.

METHODS

Children with IgAD where divided into two groups; severe IgAD in patients was defined as serum IgA level <7 mg/dL, while partial IgA deficiency diagnosis was made when serum IgA levels was higher than 7 mg/dL but at least two standard deviations (SD) below mean normal concentrations for their age. All patients were evaluated by their clinical and laboratory investigation parameters and compared to control group of children.

RESULTS

Group of children with IgAD, severe as well as partial, showed higher prevalence of allergic diseases and total number of infections, compared to controls. There was a statistically significant difference in lung function for peak expiratory flow (PEF), the maximal expiratory flow at 50% of the forced vital capacity (MEF50) and fraction of exhaled nitric oxide (FENO) between group of patients with severe as well as partial IgAD and control group, where children with IgAD showed reduced lung function.

CONCLUSIONS

Children with sIgAD are at increased risk for higher number of respiratory infections and developing allergic diseases, resulting in significantly lower pulmonary function which is related with the severity of sIgAD.

Mapping of Signaling Pathways Linked to sIgAD Reveals Impaired IL-21 Driven STAT3 B-Cell Activation

Objectives: It has recently been shown that individuals with selective IgA deficiency (sIgAD) have defective B cell responses both to T cell dependent and independent mimicking stimulations. The complex intracellular signaling pathways from different stimuli leading to IgA isotype switching have not been fully elucidated. Thus, the main objective of this study was to delineate these pathways and their potential role in the immunopathology linked to sIgAD.

Materials and Methods: PBMCs from 10 individuals with sIgAD and 10 healthy controls (HC) were activated in vitro via either a T cell dependent or independent mimicking stimulation. Intracellular phosphorylation of pSTAT3, pSTAT5, pSTAT6, and as pERK1/2 was evaluated in T and B cells using phosphoflow cytometry.

Results: By evaluating T cell dependent cytokine driven pathways linked to IgA isotype induction we identified a defect involving an IL-21 driven STAT3 activation isolated to B cells in sIgAD individuals. However, all other signaling pathways studied were found to be normal compared to HC. In T cell dependent cytokine driven stimulations linked to IgA isotype induction the following patterns emerged: (i) IL-10 led to significant STAT3 activation in both T- and B cells; (ii) IL-4 stimulation was predominantly confined to STAT6 activation in both T- and B cells, with some effects on STAT3 activation in T-cells; (iii) as expected, of tested stimuli, IL-2 alone activated STAT5 and some STAT3 activation though in both cases only in T-cells; (iv) IL-21 induced significant activation of STAT3 in both T- and B cells, with some effects on STAT5 activation in T-cells; and finally (v) synergistic effects were noted of IL-4+IL-10 on STAT5 activation in T-cells, and possibly STAT6 in both T- and B cells. On the other hand, CPG induced T cell independent activation was confined to ERK1/2 activation in B cells.

Conclusion: Our results indicate a diminished STAT3 phosphorylation following IL-21 stimulation solely in B cells from sIgAD individuals. This can represent aberrant germinal center reactions or developmental halt. Thus, our work provides further insight into the unraveling of the previously hypothesized role of IL-21 to reconstitute immunoglobulin production in primary antibody deficiencies.

A comprehensive understanding of the gut mucosal immune system in allergic inflammation

Despite its direct exposure to huge amounts of microorganisms and foreign and dietary antigens, the gut mucosa maintains intestinal homeostasis by utilizing the mucosal immune system. The gut mucosal immune system protects the host from the invasion of infectious pathogens and eliminates harmful non-self antigens, but it allows the cohabitation of commensal bacteria in the gut and the entry of dietary non-self antigens into the body via the mucosal surface. These physiological and immunological activities are regulated by the ingenious gut mucosal immune network, comprising such features as gut-associated lymphoid tissue, mucosal immune cells, cytokines, chemokines, antimicrobial peptides, secretory IgA, and commensal bacteria. The gut mucosal immune network keeps a fine tuned balance between active immunity (against pathogens and harmful non-self antigens) and immune tolerance (to commensal microbiota and dietary antigens), thus maintaining intestinal healthy homeostasis. Disruption of gut homeostasis results in persistent or severe gastrointestinal infection, inflammatory bowel disease, or allergic inflammation. In this review, we comprehensively introduce current knowledge of the gut mucosal immune system, focusing on its interaction with allergic inflammation.

Effect of route of inoculation on innate and adaptive immune responses to porcine epidemic diarrhea virus infection in suckling pigs

The effects of route of administration on systemic and gut mucosal immune responses induced by porcine epidemic diarrhea virus (PEDV) infection in suckling pigs were investigated. Twenty-four conventional 5-day-old suckling piglets were randomly divided into four groups and were inoculated orally, intranasally (I.N.), intramuscularly (I.M.) with PEDV or DMEM (mock). Pigs were monitored daily for clinical signs and fecal viral load. Blood samples were collected at 7, 14, 21 days post infection (dpi) and subjected for the analyses of serum antibody production, T cell and natural killer (NK) cell frequencies, NK cytotoxicity and serum cytokine levels. Oral inoculation led to higher levels of PEDV-specific IgA antibodies in both serum and gut mucosal sites than did other routes of inoculation. Intranasal inoculation elicited significantly higher titers of virus-specific IgG antibodies in serum. PEDV-infected pigs regardless of inoculation routes had significantly lower NK cell frequencies than those of the control pigs at 14 dpi. The orally inoculated pigs had significantly higher CD3+CD8+ T cell frequencies as compared to I.N. or I.M. inoculated pigs at 14 dpi, while there was no significant difference among orally, I.N. or I.M. inoculated pigs and control pigs in CD3+CD4+ T cell frequencies in peripheral blood. PEDV-infected and control pigs had low, but detectable NK cell activities at 14 and 21 dpi, however, NK cell activities were barely detectable at 7 dpi whether the pigs were infected or not. Serum IL-10 levels were induced drastically in orally infected pigs at 7 dpi and then gradually declined. Serum IL-12 levels followed a similar pattern while the fold-change was much lower. In conclusion, oral inoculation may generate more comprehensive immune responses.

M cell targeting engineered biomaterials for effective vaccination

Vaccines are one of the greatest medical interventions of all time and have been successful in controlling and eliminating a myriad of diseases over the past two centuries. Among several vaccination strategies, mucosal vaccines have wide clinical applications and attract considerable interest in research, showing potential as innovative and novel therapeutics. In mucosal vaccination, targeting (microfold) M cells is a frontline prerequisite for inducing effective antigen-specific immunostimulatory effects. In this review, we primarily focus on materials engineered for use as vaccine delivery platforms to target M cells. We also describe potential M cell targeting areas, methods to overcome current challenges and limitations of the field. Furthermore, we present the potential of biomaterials engineering as well as various natural and synthetic delivery technologies to overcome the challenges of M cell targeting, all of which are absent in current literature. Finally, we briefly discuss manufacturing and regulatory processes to bring a robust perspective on the feasibility and potential of this next-generation vaccine technology.

Cross-protective efficacy of dendritic cells targeting conserved influenza virus antigen expressed by Lactobacillus plantarum

Avian influenza virus (AIV) can infect birds and mammals, including humans, and are thus a serious threat to public health. Vaccination is vital for controlling AIV circulation. In this study, we generated a recombinant lactobacillus expressing the NP-M1-DCpep of H9N2 avian influenza virus and evaluated the activation effect of NC8-pSIP409-NP-M1-DCpep on dendritic cells (DCs) in a mouse model. The specific mucosal antibody responses and B and T cell responses in lymphoid tissues were also characterized. Importantly, we confirmed that specific CD8 T cells presented in vitro and antigen-specific cytotoxicity (activated the expression of CD107a) and in vivo antigen-specific cytotoxicity after vaccination. The adoptive transfer of NC8-pSIP409-NP-M1-DCpep-primed CD8+ T cells into NOD-SCID mice resulted in effective protection against mouse-adapted AIV infection. In addition, we observed protection in immunized mice challenged with mouse-adapted H9N2 AIV and H1N1 influenza virus, as evidenced by reductions in the lung virus titers, improvements in lung pathology, and weight loss and complete survival. Our data are promising for the generation of effective, non-traditional influenza vaccines against AIVs.

B-cell activation with CD40L or CpG measures the function of B-cell subsets and identifies specific defects in immunodeficient patients

Around 65% of primary immunodeficiencies are antibody deficiencies. Functional tests are useful tools to study B-cell functions in vitro. However, no accepted guidelines for performing and evaluating functional tests have been issued yet. Here, we report our experience on the study of B-cell functions in infancy and throughout childhood. We show that T-independent stimulation with CpG measures proliferation and differentiation potential of memory B cells. Switched memory B cells respond better than IgM memory B cells. On the other hand, CD40L, a T-dependent stimulus, does not induce plasma cell differentiation, but causes proliferation of naïve and memory B cells. During childhood, the production of plasmablasts in response to CpG increases with age mirroring the development of memory B cells. The response to CD40L does not change with age. In patients with selective IgA deficiency (SIgAD), we observed that switched memory B cells are reduced due to the absence of IgA memory B cells. In agreement, IgA plasma cells are not generated in response to CpG. Unexpectedly, B cells from SIgAD patients show a reduced proliferative response to CD40L. Our results demonstrate that functional tests are an important tool to assess the functions of the humoral immune system.

Mucosal vaccine delivery: Current state and a pediatric perspective

Most childhood infections occur via the mucosal surfaces, however, parenterally delivered vaccines are unable to induce protective immunity at these surfaces. In contrast, delivery of vaccines via the mucosal routes can allow antigens to interact with the mucosa-associated lymphoid tissue (MALT) to induce both mucosal and systemic immunity. The induced mucosal immunity can neutralize the pathogen on the mucosal surface before it can cause infection. In addition to reinforcing the defense at mucosal surfaces, mucosal vaccination is also expected to be needle-free, which can eliminate pain and the fear of vaccination. Thus, mucosal vaccination is highly appealing, especially for the pediatric population. However, vaccine delivery across mucosal surfaces is challenging because of the different barriers that naturally exist at the various mucosal surfaces to keep the pathogens out. There have been significant developments in delivery systems for mucosal vaccination. In this review we provide an introduction to the MALT, highlight barriers to vaccine delivery at different mucosal surfaces, discuss different approaches that have been investigated for vaccine delivery across mucosal surfaces, and conclude with an assessment of perspectives for mucosal vaccination in the context of the pediatric population.

Gut immune response in the presence of hepatitis C virus infection

Hepatitis C virus (HCV) is an important etiologic agent of hepatitis and a major cause of chronic liver infection that often leads to cirrhosis, fibrosis and hepatocellular carcinoma. Although, HCV is a hepatotropic virus, there is strong evidence that HCV could replicate extra-hepatic in the gastrointestinal tissue which could serve as a reservoir for HCV. The outcome of HCV infection depends mainly on the host innate and adaptive immune responses. Innate immunity against HCV includes mainly nuclear factor cells and activation of IFN-related genes. There is an immunologic link between the gut and the liver through a population of T-cells that are capable of homing to both the liver and gut via the portal circulation. However, little is known on the role of Gut immune response in HCV. In this review we discussed the immune regulation of Gut immune cells and its association with HCV pathogenesis, various outcomes of anti-HCV therapy, viral persistence and degree of liver inflammation. Additionally, we investigated the relationship between Gut immune responses to HCV and IL28B genotypes, which were identified as a strong predictor for HCV pathogenesis and treatment outcome after acute infection.

Children with partial IgA deficiency: clinical characteristics observed in the pediatric rheumatology clinic

Literature is lacking on partial IgA deficiency. In this study, the authors propose to describe the clinical manifestations of patients with partial IgA deficiency. Methods. The authors conducted a retrospective chart review of 13 patients with partial IgA deficiency followed at the pediatric rheumatology clinic at Robert Wood Johnson Medical School. They looked for the presence of rashes, joint pain, joint swelling, and morning stiffness. The authors also examined charts for a history of frequent infections, allergies, and the presence of elevated antinuclear antibody. Results. Eleven out of the 13 patients complained of joint pain, joint swelling, or morning stiffness. Six patients carried a diagnosis of a definitive rheumatic disease. Four patients suffered from frequent infections and 2 patients reported allergies. Conclusion. Partial IgA deficiency appears to be associated with rheumatic diseases and complaints of joint pain, joint swelling, and morning stiffness. A larger study is needed to confirm these results.

Reversible IgA deficiency after severe Gram-negative bacteria infection in a patient with systemic sclerosis

A 43-year-old woman with systemic sclerosis (SSc) developed IgA deficiency (IgAD) after cholecystitis. The severe decrease of IgA (<10 mg/dl) partially recovered after 5 years. She had repeated episodes of infection during IgAD. Anti-IgA antibody was not detected. Flow cytometric analysis showed that peripheral CD19(+)IgA(+) and CD38(+)IgA(+) cells were normally present. Although the mechanism of secondary IgAD is still vague, its association with autoimmune diseases including SSc and also with bacterial infection is discussed.

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.

[IgA subclass and IgA deficiency]

There are two subclasses of IgA, IgA1 and IgA2, and its heavy chains are encoded by two different genes, alpha1 and alpha2 genes. These two subclasses play important roles in the first line of defense, and the amount ratio of these molecules in secretions varies. IgA deficiency (IgAD) is the most common immunodeficiency, however the pathogenesis in most cases of IgAD is unknown. The class switch disorder in IgA producing B lymphocytes is one of the important factors in IgAD patients. The decreased expression levels of Ialpha germline transcripts before a class switch may be the cause of selective IgAD. The alpha1 and alpha2 gene expression levels are low in most IgAD patients. Using RT-PCR method in which alpha1 and alpha2 mRNAs can be separately evaluated, we identified the second case of alpha1 gene deletion in Japan. Longitudinal change in the serum IgA of the patient with alpha1 gene deletion showed the pattern of the partial IgAD. Patients with alpha1 gene deletion can be considered as having partial IgAD.

Dendritic cell targeting of Bacillus anthracis protective antigen expressed by Lactobacillus acidophilus protects mice from lethal challenge

Efficient vaccines potentiate antibody avidity and increase T cell longevity, which confer protection against microbial lethal challenge. A vaccine strategy was established by using Lactobacillus acidophilus to deliver Bacillus anthracis protective antigen (PA) via specific dendritic cell-targeting peptides to dendritic cells (DCs), which reside in the periphery and mucosal surfaces, thus directing and regulating acquired immunity. The efficiency of oral delivery of L. acidophilus expressing a PA-DCpep fusion was evaluated in mice challenged with lethal B. anthracis Sterne. Vaccination with L. acidophilus expressing PA-DCpep induced robust protective immunity against B. anthracis Sterne compared with mice vaccinated with L. acidophilus expressing PA-control peptide or an empty vector. Additionally, serum anti-PA titers, neutralizing PA antibodies, and the levels of IgA-expressing cells were all comparable with the historical recombinant PA plus aluminum hydroxide vaccine administered s.c. Collectively, development of this strategy for oral delivery of DC-targeted antigens provides a safe and protective vaccine via a bacterial adjuvant that may potentiate mucosal immune responses against deadly pathogens.

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.

TACI, isotype switching, CVID and IgAD

Common Variable Immunodeficiency (CVID) is the most prevalent human primary immunodeficiency requiring medical attention. Until recently the only known genetic defect specific to CVID was ICOS deficiency that accounts for about 1% of the patients analyzed. Mutations in the TNFR family member TACI (transmembrane activator and calcium-modulator and cyclophilin ligand interactor), which mediates isotype switching in B cells, were found to be present in 5% of patients with CVID. Mutations in TACI were also found in relatives of patients with CVID who suffered from IgA deficiency (IgAD) as well as in a patient with isolated IgAD. In the majority of patients described to date only one TACI allele is mutated, showing an autosomal dominant transmission of the disease. B cells from individuals with TACI mutations did not produce IgG and IgA in response to the TACI ligand, APRIL (a proliferation-inducing ligand), probably reflecting impaired isotype switching. These results suggest that TACI mutations can lead to CVID.

T and B lymphocyte subpopulations and activation/differentiation markers in patients with selective IgA deficiency

Selective deficiency of immunoglobulin A (IgAD) and common variable immunodeficiency (CVID) are genetically closely related diseases, both of unknown pathogenesis. A plethora of abnormalities in lymphocyte subpopulations and expression of activation markers were repeatedly documented in CVID patients, while almost no data are available about lymphocyte subpopulations in IgAD patients. We determined basic lymphocyte subpopulations and those subpopulations that were reported to be abnormal in CVID patients (CD25, human leucocyte antigen (HLA)-DR CD45RA, CD45RO, CD27, CD28 and CD29 on both CD4(+) and CD8(+) cells, CD57 and CD38 on CD8(+) cells, CD21, CD27, IgM, IgD on B lymphocytes) in 85 patients with IgAD, 47 patients with CVID and in 65 healthy controls. Statistical analysis was performed by the Mann-Whitney U-test; significant P-values were determined by means of Bonferoni's correction. Our results showed an increase in the relative number of CD8(+) cells and a decrease in the absolute number of CD4(+) cells compared to healthy people, but similar abnormalities in CVID patients were much more expressed. IgAD patients had significantly decreased expression of HLA-DR and increased expression of CD25 on CD4(+) lymphocytes, also CD29 expression was decreased on CD8(+) cells, while other activation/differentiation markers on T cells (including the expression of CD45RA and CD45RO antigens) were not changed. There were no statistically significant abnormalities in B lymphocyte developmental stages in IgAD patients compared to healthy controls. Our observation showed that the majority of T and B lymphocyte subpopulation abnormalities described previously in CVID are not present in IgAD patients.

Class switch recombination in selective IgA-deficient subjects

Selective IgA deficiency is a common immunodeficiency in Caucasians, but the molecular basis of the disorder remains elusive. To address this issue we examined the molecular events leading to IgA production. Naive IgD positive B cells were purified from four donors with IgA deficiency and four control donors, all Caucasians. Stimulation of B cells from IgA-deficient donors with the cytokines transforming growth factor (TGF)-beta, interferon (IFN)-gamma or interleukin (IL)-10 in the presence of anti-CD40 antibodies showed reduced expression of both activation-induced cytidine deaminase (AID) and alpha germline transcripts (GLT) compared to controls. It was possible, however, to induce AID and alpha GLT when stimulating the cells with anti-CD40 antibody and TGF-beta in the combination with IL-10. Moreover, in anti-CD40 antibody-stimulated cultures, addition of IL-10 or IL-10 + TGF-beta in combination, induced IgA production, albeit lower than found in B cells from controls. The B cells from the IgA-deficient subjects were less effective in differentiating into CD138(+) X-box binding protein 1 (XBP-1)(+) plasma cells when stimulated with TGF-beta, IFN-gamma or IL-10. Interestingly, when adding IL-4 to TGF-beta alone or in combination with IL-10, the immunoglobulin production in B cells from IgA-deficient donors was comparable with those of normal controls. These data show that in healthy subjects in vitro IgA production can be up-regulated by addition of IL-10 to CD40-stimulated B cells, whereas a similar B cell differentiation does not occur in IgA-deficient subjects. Addition of IL-4, however, reverts this abnormality.

Mucosal B cell deficiency in IgA-/- mice abrogates the development of allergic lung inflammation

We have investigated the consequence of lack of IgA on host immunity using a murine model of allergic lung inflammation. Mice with a targeted disruption of the alpha-switch region and 5' H chain gene (IgA(-/-) mice), which lack total IgA, developed significantly reduced pulmonary inflammation with fewer inflammatory cells in lung tissue and bronchoalveolar lavage fluids, as well as reduced levels of total and IgG1 OVA-specific Abs and decreased IL-4 and IL-5 in bronchoalveolar lavage fluids compared with IgA(+/+) controls, following allergen sensitization and challenge. This defect was attributable to fewer B cells in the lungs of IgA(-/-) mice. Polymeric IgR-deficient (pIgR(-/-)) mice, which lack the receptor that transports polymeric IgA across the mucosal epithelium where it is cleaved to form secretory IgA, were used to assess the contribution of secretory IgA vs total IgA in the induction of allergic lung inflammation. pIgR(-/-) and pIgR(+/+) mice had comparable levels of inflammation, demonstrating that IgA bound to secretory component is not necessary for the development of allergic lung inflammation, although this does not necessarily rule out a role for transudated IgA in lung secretions because of "mucosal leakiness" in these mice. The results indicate that Ag-specific B cells are required at mucosal surfaces for induction of inflammation and likely function as major APCs in the lung for soluble protein Ags.

TACI is mutant in common variable immunodeficiency and IgA deficiency

The tumor necrosis factor receptor family member TACI (transmembrane activator and calcium-modulator and cyclophilin ligand interactor) mediates isotype switching in B cells. We found that 4 of 19 unrelated individuals with common variable immunodeficiency (CVID) and 1 of 16 individuals with IgA deficiency (IgAD) had a missense mutation in one allele of TNFRSF13B (encoding TACI). One of the four individuals with CVID had a single nucleotide insertion in the other TNFRSF13B allele. None of these mutations were present in 50 healthy subjects. TNFRSF13B mutations cosegregated with the phenotype of CVID or IgAD in family members of four index individuals that we studied. B cells from individuals with TACI mutations expressed TACI but did not produce IgG and IgA in response to the TACI ligand APRIL, probably reflecting impaired isotype switching. These results suggest that TACI mutations can result in CVID and IgAD.

Mucosal immunity and vaccines

There is currently great interest in developing mucosal vaccines against a variety of microbial pathogens. Mucosally induced tolerance also seems to be a promising form of immunomodulation for treating certain autoimmune diseases and allergies. Here we review the properties of the mucosal immune system and discuss advances in the development of mucosal vaccines for protection against infections and for treatment of various inflammatory disorders.