Common variable immunodeficiency: The power of co-stimulation

Enhanced B Cell Receptor Signaling Partially Compensates for Impaired Toll-like Receptor 4 Responses in LPS-Stimulated IκBNS-Deficient B Cells

Lipopolysaccharide (LPS) stimulates dual receptor signaling by bridging the B cell receptor and Toll-like receptor 4 (BCR/TLR4). B cells from IκBNS-deficient bumble mice treated with LPS display reduced proliferative capacity and impaired plasma cell differentiation. To improve our understanding of the regulatory role of IκBNS in B cell activation and differentiation, we investigated the BCR and TLR4 signaling pathways separately by using dimeric anti-IgM Fab (F(ab')₂) or lipid A, respectively. IκBNS-deficient B cells exhibited reduced survival and defective proliferative capacity in response to lipid A compared to B cells from wildtype (wt) control mice. In contrast, anti-IgM stimulation of bumble B cells resulted in enhanced viability and increased differentiation into CD138⁺ cells compared to control B cells. Anti-IgM-stimulated IκBNS-deficient B cells also showed enhanced cycle progression with increased levels of c-Myc and cyclin D2, and augmented levels of pCD79a, pSyk, and pERK compared to control B cells. These results suggest that IκBNS acts as a negative regulator of BCR signaling and a positive regulator of TLR4 signaling in mouse B cells.

A case of progressive multifocal leukoencephalopathy with hypogammaglobulinemia and a TCF3 mutation

Progressive multifocal leukoencephalopathy (PML) is a rare and potentially fatal demyelinating disease of the central nervous system (CNS) caused by JC virus; it was previously seen predominantly in immunocompromised patients and those under intense immune suppression. Here, we report the case of a patient with PML with hypogammaglobulinemia and a heterozygous mutation in the TCF3 gene. As the TCF3 gene has been demonstrated to play an important role in the B cell differentiation process and the patient had no other medical history of the immune system, he was diagnosed with common variable immunodeficiency (CVID). To our knowledge, this is the first case of patient with a TCF3 gene deficiency and hypogammaglobulinemia who developed PML.

Dysregulatory processes of the cellular link of the immune system in the dynamics of common variable immunodeficiency

Common variable immunodeficiency (CVID) is a variant of primary immunodeficiency in which inhibition of antibody production is formed due to disorders of intercellular interaction affecting cellular elements of both innate and adaptive immune responses. A feature of CVID is the late start and variability of clinical minifestation. These arguments determine the purpose of the study: to identify the dynamics of changes in the cellular parameters of the adaptive and innate immune response depending on the duration and severity of the infectious manifestation of CVID. In this regard, a retrospective analysis of medical histories and dynamic observation of fifteen patients with CVID were carried out. Selection of specific parameters of cellular indices of factors of innate resistance and adaptive immunity was carried out on the basis of systemic-functional approach of immunodiagnostics. It is shown that in patients with CVID -mediated hypogammaglobulinemia and infectious phenotype of clinical manifestation, enhancement of quantitative and functional potentials of T-link effector cells of adaptive immunity is recorded against the background of reduction of number of regulatory T-helpers. With a more severe clinical course of the disease, the number of CD3+HLA DR + limphocytes is lower than with a more favorable version, there is a tendency to decrease the number of these cells, as well as the number of peripheral Treg with an increase in the length of the disease. Cellular components of innate immunity are characterized by a decrease in neutrophil activity, inhibition of antigen-presenting monocyte activity, the number and cytotoxicity of natural killers. At the same time, the tendency to decrease the cytolytic potential of NK with an increase in the length of illness and statistically significant differences depending on the severity of the manifestation of the infectious phenotype of CVID was recorded. The obtained results determine the importance of evaluating the cellular link of the immune system in patients with CVID, including as a prognostic criterion for the severity of the course.

Characteristics of the patients followed with the diagnosis of common variable immunodeficiency and the complications

Introduction

In this study, we aimed to retrospectively evaluate the clinical and laboratory findings and complications of 28 common variable immunodeficiency (CVID) patients.

Material and methods

The clinical features and laboratory data of 28 CVID patients were evaluated.

Results

Nineteen patients were male. In 53.5% of the cases, complications included inflammatory bowel disease, cytopenia, bronchiectasis, granulomatous lymphocytic interstitial lung disease (ILD) and asthma. In their immunological evaluations, IgG, IgM, and IgA mean values were 474.8 ±214.1 mg/dl; 56.7 ±41.9 mg/dl; 35.3 ±58.2 mg/dl, respectively, and the vaccine response was positive in 64.2% of the cases. In all age groups, absolute lymphocyte counts, naive (CD19+IgD+27-), nonswitch (CD19+IgD-27+) memory B cells were numerically higher when compared to the data of healthy children; however, although switch memory (CD19+IgD+27+) B cells were proportionally low in the 4-8 and 12-18 age groups, they were low both numerically and proportionally in the 8-12 age group. No statistically significant difference was found between the cases with complications and without complications. But the cases with pulmonary complications were compared within the group, the CD8 ratio was high but the IgA level was low in patients with bronchiectasis and CD3 was numerically and proportionally low in the cases with ILD compared to others. According to the Paris classification, 11/27 (40.7%) of the cases, 3/27 (11.1%) of them and 13/27 (48.2%) of them were evaluated as MB0, MB1, and MB2, respectively.

Conclusions

In genetic studies, TACI (trans-membrane activator and calcium-modulating cyclophilin ligand interactor – TNFRSF13B) mutation was found positive in 25% of the cases.

Phenotyping and follow up of forty-seven Iranian patients with common variable immunodeficiency

BACKGROUND

Common variable immune deficiency (CVID) is a heterogeneous syndrome with a wide variety of signs and symptoms. This study describes the phenotyping and survival of the CVID patients in the allergy and clinical immunology department of Rasol-E-Akram Hospital of Iran University of Medical Sciences in Tehran.

METHOD

We retrospectively reviewed hospital files of CVID patients in our department until January 2014. All patients were diagnosed with standard diagnostic criteria of CVID, treated and visited monthly, during the follow-up period. We divided the patients into four phenotypes; infection only, cytopenia, polyclonal lymphocytic infiltration and unexplained enteropathy. The immunologic, demographic and clinical findings in different phenotypes were analysed.

RESULTS

The study included 47 CVID patients with mean age at onset of symptoms and diagnosis of 11.2 and 20.2 years, respectively. Phenotyping of our patients was: only infection (62%), cytopenia (26%) and PLI (19%) and 94% of cases had only one phenotype. We did not find a significant relation between the clinical phenotypes and immunologic or demographic data. Rate of parental consanguinity in our cases was 47%. Parental consanguinity was related to lower age at onset, lower age at diagnosis and higher baseline IgG levels. Patients with malignancy and autoimmunity had significantly higher age at onset. Our patients were followed-up for 6.9 years and the mortality rate during this time was 6%.

CONCLUSIONS

Parental consanguinity and age at onset of CVID symptoms may have important roles in CVID manifestations.

CD4+CD25+Foxp3+ T regulatory cells, Th1 (CCR5, IL-2, IFN-γ) and Th2 (CCR4, IL-4, Il-13) type chemokine receptors and intracellular cytokines in children with common variable immunodeficiency

Common variable immunodeficiency (CVID) is a heterogeneous group of primary antibody deficiencies characterized by decreased serum immunoglobulin G along with a decrease in serum IgA and/or IgM, defective specific antibody production, and recurrent bacterial infections. Abnormal lymphocyte trafficking, dysregulated cellular responses to chemokines, and uncontrolled T cell polarization may be involved in the pathogenesis and may help to understand the clinical complications. We evaluated T helper cell subsets (chemokine receptors CCR4, CCR5, and CCR7), expressions on T lymphocytes, intracellular cytokines - IL-2, IL-4, IL-13, IFN- γ-on CD4(+) T cells, and expression of CD4(+)CD25(+)Foxp3(+) regulatory T cells of 20 CVID patients and 26 healthy controls. Autoimmune clinical findings and other complications were also determined. Percentages and absolute numbers of CD4(+)CD25(+) Foxp3(+) cells did not show any significant difference between CVID cases and healthy controls nor between severe and moderate disease patients. The only significant difference regarding Th1 and Th2 type intracellular cytokines was the decreased absolute numbers of CD3(+)CD4(+)IL4(+) cells in CVID cases. There were some findings about T helper cell type dominance in CVID patients such as positive correlation between hepatomegaly and high IL-2 and IFN-γ in CD3(+)CD4(+) cells and very high expression of CCR5 (Th1) on CD3(+)CD4(+) cells in patients with granuloma. Th1 (CCR5) and Th2 (CCR4) type chemokine receptors did not show any dominance in CVID cases. However, frequencies of CCR7 expressing CD3(+) T cells, CD3(+)CD4(+) T helper cells and CD3(+)CD8(+) T cytotoxic cells were significantly lower in severe CVID patients. In addition, presence of autoimmune clinical findings was negatively correlated with CCR7(+) cells. As CCR7 is a key mediator balancing immunity and tolerance in the immune system, the abnormality of this mediator may contribute to the profound immune dysregulation seen in CVID. In addition, Th1 cells seem to be more involved in the disease pathogenesis than Th2 cells.

Inflammatory bowel disease-like colitis pathology in a patient with common variable immune deficiency

Common variable immunodeficiency (CVID) can show variant histological patterns in the gastrointestinal system. We present a case of an 11-year-old boy who has been followed up with a diagnosis of CVID since he was 6 months old. He presented with abdominal pain and diarrhoea. Colonoscopic biopsy showed crypt destructive colitis, severe decrease and focal absence of plasma cells. Three months later he suffered from abdominal pain, vomiting and bloody diarrhoea. Macroscopic examination of small intestinal resection material revealed multiple perforation areas, ulcers. Histopathology showed mild-moderate active enteritis with aphthous ulcers, purulent peritonitis, decrease in plasma cells and loss of primary follicles in lymph nodes. Histopathological findings were consistent with inflammatory bowel disease (IBD)-like CVID. Although in 6-10% of patients with CVID an IBD-like presentation is observed, this highly aggressive form is rarely seen. We present this case because of its extraordinary presentation displaying perforating active enteropathy.

Retinoic acid improves defective TLR9/RP105-induced immune responses in common variable immunodeficiency-derived B cells

Common variable immunodeficiency (CVID) is a disease that is characterized primarily by low levels of serum Igs, resulting in a high incidence of infections. It also has been associated with impaired B cell signaling via TLR9 and reduced serum levels of vitamin A. Given the established link between vitamin A deficiency and increased susceptibility to infections, we investigated the ability of the vitamin A metabolite all-trans retinoic acid (RA) to restore the defective immune responses in CVID-derived B cells activated through the TLRs TLR9 and RP105. We demonstrate that RA almost normalizes proliferation and IL-10 secretion in patient-derived B cells. IgG secretion is also partially restored, but to a more moderate extent. This can be explained by impaired RA-mediated isotype switching in TLR9/RP105-stimulated CVID-derived B cells owing to reduced induction of activation-induced deaminase. Accordingly, these B cells secreted higher levels of IgM than did normal B cells, and RA augmented IgM secretion. The ability of RA to improve critical immune parameters in CVID-derived B cells stimulated through TLR9 and RP105 support the possibility of combining RA with TLR stimulation for the treatment of CVID.

Nodular regenerative hyperplasia in common variable immunodeficiency

PURPOSE

Patients with Common Variable Immunodeficiency (CVID) are subject to the development of a liver disease syndrome known as nodular regenerative hyperplasia (NRH). The purpose of this study was to define the characteristics and course of this complication of CVID.

METHODS

CVID patients were evaluated by retrospective and prospective clinical course review. Liver biopsy specimens were evaluated for evidence of NRH and studied via RT-PCR for cytokine analysis.

RESULTS

NRH in our CVID patient population occurred in approximately 5 % of the 261 patients in our total CVID study group, initially presenting in most cases with an elevated alkaline phosphatase level. While in some patients the disease remained static, in a larger proportion a more severe disease developed characterized by portal hypertension, the latter leading to hypersplenism with neutropenia and thrombocytopenia and, in some cases, to ascites. In addition, a substantial proportion of patients either developed or presented initially with an autoimmune hepatitis-like (AIH-like) liver disease that resulted in severe liver dysfunction and, in most cases to death due to infections. The liver histologic findings in these AIH-like patients were characterized by underlying NRH pattern with superimposed interface hepatitis, lymphocytic infiltration and fibrosis. Immunologic studies of biopsies of NRH patients demonstrated the presence of infiltrating T cells producing IFN-γ, suggesting that the NRH is due to an autoimmune process.

CONCLUSION

Overall, these studies provide evidence that NRH may not be benign but, can be a severe and potentially fatal disease complication of CVID that merits close monitoring and intervention.

Three different classifications, B lymphocyte subpopulations, TNFRSF13B (TACI), TNFRSF13C (BAFF-R), TNFSF13 (APRIL) gene mutations, CTLA-4 and ICOS gene polymorphisms in Turkish patients with common variable immunodeficiency

B lymphocyte subpopulations, previously defined classification schemes (Freiburg, Paris, EuroClass), TNFRSF13B (TACI), TNFRSF13C (BAFF-R), TNFSF13 (APRIL) gene mutations, CTLA-4 and ICOS gene polymorphisms were analyzed in 25 common variable immunodeficiency (CVID) patients and 25 healthy controls. Patients were also divided into two subgroups due to some disease severity criteria. SG (severe disease group) (n:11) included patients who have splenomegaly and/or granulomatous diseases and/or bronchiectasis and/or lower baseline IgG values (<270 mg/dl). MG (moderate disease group) (n:14) patients diagnosed as having ESID/PAGID criteria but does not fulfill SG inclusion criteria. The onset of infectious symptoms and age at diagnosis were 50.0 ± 45.7 and 78.5 ± 54.5 months, respectively. Parental consanguinity rate was 54.5% in SG and 7.1% in MG. Switched-memory B cells (CD19 + 27 + IgD-IgM-) showed significant decrease in CVID patients and these cells were also significantly lower in SG compared to MG. CVID patients had significantly higher percentages of CD19 + κ + B cells and CD19 + λ + B cells than healthy controls. Freiburg classification: 87.5% of patients (n:21) were in group I and 12.5% were in Group II. Eighteen (75%) CVID patients with a low percentage of CD21(low) B cells were in Group Ib while three patients classified as Group Ia. The significantly lower levels of IgG and IgA in Group Ia is a novel finding. The percentages of patients for Paris Classification groups MB0, MB1, MB2 were 88%, 4% and 8%, respectively. There was a significant increase of splenomegaly, lymphadenopathy and autoimmune cytopenia in Group MB0. EuroClass: 45.8% of patients were smB+ and 54.2% were smB-. Splenomegaly and lymphadenopathy were significantly higher in smB- group. TACI: One patient carried heterozygous C104R mutation which was known as disease causing. APRIL: G67R and N96S SNPs were detected in most of the patients and healthy controls. BAFF-R: P21R/H159Y compound heterozygous mutation (n:1) and P21R heterozygous mutations (n:3) were detected. +49 A > G changes in exon 1 of CTLA-4 gene: GG and AG genotypes increase the risk of CVID development 1.32 and 2.18 fold, respectively. 1564 T > C polymorphisms on 3'UTR region in exon 2 of ICOS gene was not found to be significantly different in CVID patients. CVID classifications were not helpful in determining the genetic etiology of CVID.

Intravenous immunoglobulin induces proliferation and immunoglobulin synthesis from B cells of patients with common variable immunodeficiency: a mechanism underlying the beneficial effect of IVIg in primary immunodeficiencies

Common variable immunodeficiency (CVID) is associated with low serum immunoglobulin concentrations and an increased susceptibility to infections and autoimmune diseases. The treatment of choice for CVID patients is replacement intravenous immunoglobulin (IVIg) therapy. IVIg has been beneficial in preventing or alleviating the severity of infections and autoimmune and inflammatory process in majority of CVID patients. Although the mechanisms of action of IVIg given as 'therapeutic high dose' in patients with autoimmune diseases are well studied, the underlying mechanisms of beneficial effects of IVIg in primary immunodeficiencies are not completely understood. Therefore we investigated the effect of 'replacement dose' of IVIg by probing its action on B cells from CVID patients. We demonstrate that IVIg at low doses induces proliferation and immunoglobulin synthesis from B cells of CVID patients. Interestingly, B cell stimulation by IVIg is not associated with induction of B cell effector cytokine IFN-γ and of transcription factor T-bet. Together, our results indicate that in some CVID patients, IVIg rectifies the defective signaling of B cells normally provided by T cells and delivers T-independent signaling for B cells to proliferate. IVIg 'replacement therapy' in primary immunodeficiencies is therefore not a merepassive transfer of antibodies to prevent exclusively the recurrent infections; rather it has an active role in regulating autoimmune and inflammatory responses through modulating B cell functions and thus imposing dynamic equilibrium of the immune system.

The B-lymphoid Grb2 interaction code

The growth factor receptor-bound protein 2 (Grb2) is a ubiquitously expressed and evolutionary conserved adapter protein possessing a plethora of described interaction partners for the regulation of signal transduction. In B lymphocytes, the Grb2-mediated scaffolding function controls the assembly and subcellular targeting of activating as well as inhibitory signalosomes in response to ligation of the antigen receptor. Also, integration of simultaneous signals from B-cell coreceptors that amplify or attenuate antigen receptor signal output relies on Grb2. Hence, Grb2 is an essential signal integrator. The key question remains, however, of how pathway specificity can be maintained during signal homeostasis critically required for the balance between immune cell activation and tolerance induction. Here, we summarize the molecular network of Grb2 in B cells and introduce a proteomic approach to elucidate the interactome of Grb2 in vivo.

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: etiological and treatment issues

One of the great advances in clinical medicine was the recognition of the pleomorphism of the immune response and the multiple afferent and efferent limbs of antigen processing and responsiveness. A significant contribution to this understanding was derived from studies of human immunodeficiency states, including both inherited and acquired syndromes. Amongst these syndromes, one of the most common, and least understood, is common variable immune deficiency (CVID). CVID is a syndrome that leads to a reduction in serum immunoglobulins and complications including recurrent infections. Management includes immunoglobulin replacement therapy; however, patients with CVID are at risk for complications of exogenous immunoglobulin administration as well as CVID-associated diseases such as autoimmune processes and malignancies. To assess the current state of knowledge in the field, we performed a literature review of a total of 753 publications covering the period of 1968 until 2008. From this list, 189 publications were selected for discussion. In this review, we demonstrate that while the molecular basis of CVID in many cases remains incompletely understood, significant strides have been made and it is now clear that there is involvement of several pathways of immune activation, with contributions from both T and B cells. Furthermore, despite the current gaps in our knowledge of the molecular pathogenesis of the syndrome, there have been dramatic advances in management that have led to improved survival and significantly reduced morbidity in affected patients.

The B-cell compartment in the peripheral blood of children with different types of primary humoral immunodeficiency

The aim of this study was to evaluate the B-cell compartment in the peripheral blood of children with different types of hypogammaglobulinemia: common variable immunodeficiency (CVID), transient hypogammaglobulinemia of infancy (THI), and selective IgA deficiency (SIgAD). We analyzed by flow cytometry the changes in the B-cell subsets with age and showed that children with an early-onset CVID develop similar pattern of B-cell subsets as adult patients with CVID with age, as the levels of memory B cells (CD19/CD27) and class-switched memory B cells (CD19/CD27/IgD/IgM), in contrast to age-matched control group, did not increase with age. Children with SIgAD displayed similar changes as patients with CVID only within the class-switched memory B-cell subpopulation. No significant differences in the level of memory B cells and class-switched memory B cells in children with THI in comparison to age-matched control group were observed. There were no differences in the percentage of immature B cells (CD19/CD21) among all studied groups. As B-cell subsets in children with THI were normal during entire period of hypogammaglobulinemia, the persistence of low levels of memory B-cell subsets in some children may facilitate the diagnosis of CVID.

Impaired CD4 and CD8 effector function and decreased memory T cell populations in ICOS-deficient patients

Interaction of ICOS with its ligand is essential for germinal center formation, T cell immune responses, and development of autoimmune diseases. Human ICOS deficiency has been identified worldwide in nine patients with identical ICOS mutations. In vitro studies of the patients to date have shown only mild T cell defect. In this study, we report an in-depth analysis of T cell function in two siblings with novel ICOS deficiency. The brother displayed mild skin infections and impaired Ig class switching, whereas the sister had more severe symptoms, including immunodeficiency, rheumatoid arthritis, inflammatory bowel disease, interstitial pneumonitis, and psoriasis. Despite normal CD3/CD28-induced proliferation and IL-2 production in vitro, peripheral blood T cells in both patients showed a decreased percentage of CD4 central and effector memory T cells and impaired production of Th1, Th2, and Th17 cytokines upon CD3/CD28 costimulation or PMA/ionophore stimulation. The defective polarization into effector cells was associated with impaired induction of T-bet, GATA3, MAF, and retinoic acid-related orphan nuclear hormone receptor (RORC). Reduced CTLA-4(+)CD45RO(+)FoxP3(+) regulatory T cells and diminished induction of inhibitory cell surface molecules, including CTLA-4, were also observed in the patients. T cell defect was not restricted to CD4 T cells because reduced memory T cells and impaired IFN-gamma production were also noted in CD8 T cells. Further analysis of the patients demonstrated increased induction of receptor activator of NF-kappaB ligand (RANKL), lack of IFN-gamma response, and loss of Itch expression upon activation in the female patient, who had autoimmunity. Our study suggests that extensive T cell dysfunction, decreased memory T cell compartment, and imbalance between effector and regulatory cells in ICOS-deficient patients may underlie their immunodeficiency and/or autoimmunity.

Genetic defects of apoptosis and primary immunodeficiency

Programmed cell death is important for maintaining lymphocyte homeostasis. Several human-inherited diseases with impaired apoptosis have been identified at the genetic level: autoimmune lymphoproliferative syndrome, caspase-8 deficiency state, and X-linked lymphoproliferative syndrome. These diseases feature excess lymphocyte accumulation, autoimmunity, or immunodeficiency. Elucidating their molecular pathogenesis has also provided new insights into the signaling mechanisms regulating apoptosis and lymphocyte activation.

Revisiting human primary immunodeficiencies

Human primary immunodeficiencies (PIDs) are often thought to be confined to a few rare, familial, monogenic, recessive traits impairing the development or function of one or several leucocyte subsets and resulting in multiple, recurrent, opportunistic and fatal infections in infancy. We highlight here the rapidly growing number of exceptions to each of these conventional qualifications. Indeed, bona fide PIDs include common and sporadic illnesses and may present as dominant, or even polygenic traits; their pathogenesis may involve non haematopoietic cells, and they may result in single episode of illness, with a single or multiple morbid phenotypes, some of which may involve infection, in otherwise healthy adults. We need to increase awareness of the multitude of clinical presentations of human PIDs considerably and rapidly in the medical community. Human PIDs should be considered in a wide range of clinical situations.

Down-regulation of ICOS ligand by interaction with ICOS functions as a regulatory mechanism for immune responses

Although it is well-known that the ICOS-ICOS ligand (ICOSL) costimulatory pathway is important for many immune responses, recent accumulated evidence suggests that dysregulation of this pathway may lead to and/or exaggerate autoimmune responses. ICOS is induced on the cell surface after T cell activation. Similarly, ICOSL is up-regulated on APCs by several mitogenic stimuli. However, the mechanism regulating expression of the ICOS-ICOSL pair, and the significance of controlling their expression for an appropriate immune response, is largely unknown. To gain a better understanding of the importance of fine control of the ICOS-ICOSL costimulatory pathway, we generated ICOS-transgenic (Tg) mice that have high constitutive expression of ICOS in all T cells. Using ICOS-Tg mice, we studied whether in vivo immune responses were affected. Unexpectedly, we first found that ICOS-Tg mice exhibited a phenotype resembling ICOS-deficient mice in their Ag-specific Ab response, such as a defect in class switch recombination. Further examination revealed that ICOSL expression of APCs was significantly suppressed in ICOS-Tg mice. Interestingly, suppression of ICOSL was induced by interaction of ICOSL with ICOS, and it seemed to be regulated at the posttranscriptional level. The suppressive effect of the ICOS-ICOSL interaction overcame the positive effect of CD40 or B cell activation factor of the TNF family (BAFF) stimulation on ICOSL expression. Together, our studies demonstrate a novel mechanism for the regulation of ICOSL expression in vivo and suggest that the ICOS costimulatory pathway is subject to negative feedback regulation by ICOSL down-regulation in response to ICOS expression.

Sheepish B cells: evidence for antigen-independent antibody diversification in humans and mice

Antibody diversity is first generated by rearrangement of immunoglobulin (Ig) genes during B cell development in the bone marrow, and later by antigen-driven diversification in germinal centers (GCs). New data in humans and mice now identify specific B cell populations that may have undergone antigen-independent hypermutation outside GCs.

MHC class II antigen presentation and immunological abnormalities due to deficiency of MHC class II and its associated genes

Antigen presentation by Major Histocompatibility Complex (MHC) class II molecules plays an important role in controlling immunity and autoimmunity. Multiple co-factors including the invariant chain (Ii), HLA-DM and HLA-DO are involved in this process. While the role for Ii and DM has been well defined, the biological function of DO remains obscure. Our data indicate that DO inhibits presentation of endogenous self-antigens and that developmentally-regulated DO expression enables antigen presenting cells to preferentially present different sources of peptide antigens at different stages of development. Disruption of this regulatory mechanism can result in not only immunodeficiency but also autoimmunity. Despite the fact that deletion of each of the three genes in experimental animals is associated with profound immunological abnormalities, no corresponding human diseases have been reported. This discrepancy suggests the possibility that primary immunodeficiencies due to a genetic defect of Ii, DM and DO in humans are under diagnosed or diagnosed as "common variable immunodeficiency", a category of immunodeficiency of heterogeneous or undefined etiology. Clinical tests for any of these potential genetic defects are not yet available. We propose the use of multi-color flow cytometry in conjunction with intracellular staining to detect expression of Ii, DM, DO in peripheral blood B cells as a convenient reliable screening test to identify individuals with defects in antigen presentation.

Common variable immunodeficiency disorders: division into distinct clinical phenotypes

The European Common Variable Immunodeficiency Disorders registry was started in 1996 to define distinct clinical phenotypes and determine overlap within individual patients. A total of 7 centers contributed patient data, resulting in the largest cohort yet reported. Patients (334), validated for the diagnosis, were followed for an average of 25.6 years (9461 patient-years). Data were used to define 5 distinct clinical phenotypes: no complications, autoimmunity, polyclonal lymphocytic infiltration, enteropathy, and lymphoid malignancy. A total of 83% of patients had only one of these phenotypes. Analysis of mortality showed a considerable reduction in the last 15 years and that different phenotypes were associated with different survival times. Types of complications and clinical phenotypes varied significantly between countries, indicating the need for large, international registries. Ages at onset of symptoms and diagnosis were shown to have a Gaussian distribution, but were not useful predictors of phenotype. The only clinical predictor was polyclonal lymphocytic infiltration, which was associated with a 5-fold increased risk of lymphoid malignancy. There was widespread variation in the levels of serum immunoglobulin isotypes as well as in the percentages and absolute numbers of B cells, confirming the heterogeneity of these conditions. Higher serum IgM and lower circulating CD8 proportions were found to be predictive markers for polyclonal lymphocytic infiltration and autoimmunity, respectively.

Gastrointestinal tract pathology in patients with common variable immunodeficiency (CVID): a clinicopathologic study and review

BACKGROUND

Common variable immunodeficiency (CVID) is characterized by a host of gastrointestinal (GI) lesions that can mimic other conditions.

METHODS

We reviewed clinical documentation and samples from 132 separate GI biopsy or resection sites on 20 CVID patients obtained over a 26-year period, including biopsies from the colon (34), esophagus (19), small intestine (38), and stomach (35), a partial gastrectomy, small bowel resection, colectomy, 2 cholecystectomies, and 1 appendectomy.

RESULTS

There were 13 males and 7 females. Nine patients were children (10 y and younger) and 11 were adults. Age at diagnosis ranged from 6 months to 62 years (median, 35.5 y), and age at biopsy ranged from 10 months to 67 years (median, 38 y). Esophageal samples often showed intraepithelial neutrophils, accompanied by candida. Half of patients' esophageal biopsies had prominent intraepithelial lymphocytosis, one of which also had prominent apoptosis. The stomachs of 67% of patients lacked plasma cells. Most showed lymphoid aggregates. An increase in apoptosis was detected in biopsies from a third. About 20% had a lymphocytic gastritis pattern. Intraepithelial neutrophils were found in a subset, accompanied by various infections [cytomegalovirus (CMV), Helicobacter pylori, and Cryptosporidium]. Granulomas were found in 1 patient. Gastric adenocarcinoma was identified in one patient. There was a paucity of small bowel plasma cells in the majority of patients (68%). The small bowel showed prominent lymphoid aggregates in about half (47%). An increase in apoptosis was detected in specimens from about 20%. Increased intraepithelial lymphocytes (IELs) were found in samples from over half of patients (63%), most of whom (83%) also had villous blunting, mimicking celiac disease. Intraepithelial neutrophils were found in a subset (32%) and correlated with CMV and Cryptosporidium infections. Granulomas were seen in biopsies from 2 patients (11%). One patient had a collagenous enteritis pattern (accompanied by a collagenous colitis pattern). One patient had autoimmune enteritis; biopsies from this patient were initially relatively normal but later displayed prominent crypt apoptosis and loss of goblet cells. In colon samples, a paucity of plasma cells was seen in 10 patients (63%). The colon showed lymphoid aggregates in most patients (81%). Apoptosis was prominent in samples from half of the patients (50%). Biopsies from 6 patients had a lymphocytic colitis pattern (38%) and 2 patients had a collagenous colitis pattern. Intraepithelial neutrophils were found in samples from most patients (88%). Crypt distortion was seen in 6 of these patients (43%), thereby mimicking ulcerative or Crohn colitis. Granulomas were found in 3 patients (19%). CMV was detected in 1 patient. The appendix from 1 patient showed Cryptosporidium and acute serositis with a paucity of plasma cells and an increase in apoptosis. The gallbladder from 1 patient showed acute cholecystitis, and another patient's gallbladder lacked plasma cells.

CONCLUSIONS

GI tract CVID displays a wide spectrum of histologic patterns. Its features can mimic lymphocytic colitis, collagenous enterocolitis, celiac disease, lymphocytic gastritis, granulomatous disease, acute graft-versus-host disease, and inflammatory bowel disease. In fact, in our series, we found patients with a prior diagnosis of celiac disease (25%) and inflammatory bowel disease (35%), including Crohn disease (15%). The diagnosis of CVID may be suspected on the basis of the lack of plasma cells in a GI biopsy, but because this feature is only present in about two-thirds of patients, the diagnosis cannot always be suggested in isolation of other clinical and laboratory findings.

Fungal infections in primary immunodeficiencies

Patients with phagocytic, cellular, combined and other primary immunodeficiencies exhibit immune deficits that confer increased susceptibility to fungal infections. A number of yeasts and moulds, most commonly Candida and Aspergillus but also Cryptococcus, Histoplasma, Paecilomyces, Scedosporium, Trichosporon, Penicillium and other, rarely isolated, fungal organisms, have been variably implicated in causing disease in patients with chronic granulomatous disease, severe combined immunodeficiency, chronic mucocutaneous candidiasis, hyper-IgE syndrome, myeloperoxidase deficiency, leukocyte adhesion deficiency, defects in the interferon-gamma/interleukin-12 axis, DiGeorge syndrome, X-linked hyper-IgM syndrome, Wiskott-Aldrich syndrome and common variable immunodeficiency. Differences in the spectrum of fungal pathogens as well as in the incidence and clinical presentation of the infections may be observed among patients, depending upon different immune disorders. Fungal infections in these individuals may occasionally be the presenting clinical manifestation of a primary immunodeficiency and can cause significant morbidity and potentially fatal outcome if misdiagnosed or mistreated. A high degree of suspicion is needed and establishment of diagnosis should actively be pursued using appropriate imaging, mycological and histological studies. A number of antifungal agents introduced over the last fifteen years, such as the lipid formulations of amphotericin B, the second-generation triazoles, and the echinocandins, increase the options for medical management of these infections. Surgery may also be needed in some cases, while the role of adjunctive immunotherapy has not been systematically evaluated. The low incidence of primary immunodeficiencies in the general population complicates single-center prospective or retrospective clinical studies aiming to address diagnostic or therapeutic issues pertaining to fungal infections in these patients.

An important role for B-cell activation factor and B cells in the pathogenesis of Sjögren's syndrome

PURPOSE OF REVIEW

This review provides an update on the specific, strong association between dysregulated production of the cytokine B-cell activation factor and Sjögren's syndrome, and offers new perspectives on potential pathogenic mechanisms.

RECENT FINDINGS

Excess B-cell activation factor in mice triggers Sjögren's syndrome-like symptoms, and elevated serum B-cell activation factor in humans correlates with Sjögren's syndrome. B-cell activation factor is produced locally by activated monocytes, T cells and dendritic cells, and by epithelial cells and infiltrating B cells. Moreover, recent data in humans suggest that the innate immune system plays a role as an initiator of immune disorders in inflamed tissues.

SUMMARY

Recent data have demonstrated the critical role of B-cell activation factor and B cells in the pathogenesis of Sjögren's syndrome, and its association with B lymphomas. Moreover, B-cell depleting treatments have confirmed the critical role of B cells in Sjögren's syndrome. Excess B-cell activation factor possibly corrupts B-cell tolerance and allows the emergence of self-reactive B cells that efficiently present antigen to T cells. In addition, B-cell activation factor may stimulate T-cell independent activation of B cells via Toll-like receptors; this recently identified mechanism could also play a separate, detrimental role in autoimmunity.

Primary immunodeficiencies: a field in its infancy

A paradigm shift is occurring in the field of primary immunodeficiencies, with revision of the definition of these conditions and a considerable expansion of their limits. Inborn errors of immunity were initially thought to be confined to a few rare, familial, monogenic, recessive traits impairing the development or function of one or several leukocyte subsets and resulting in multiple, recurrent, opportunistic, and fatal infections in infancy. A growing number of exceptions to each of these conventional qualifications have gradually accumulated. It now appears that most individuals suffer from at least one of a multitude of primary immunodeficiencies, the dissection of which is helping to improve human medicine while describing immunity in natura.

Calcium signalling in lymphocyte activation and disease

Calcium signals in cells of the immune system participate in the regulation of cell differentiation, gene transcription and effector functions. An increase in intracellular levels of calcium ions (Ca2+) results from the engagement of immunoreceptors, such as the T-cell receptor, B-cell receptor and Fc receptors, as well as chemokine and co-stimulatory receptors. The major pathway that induces an increase in intracellular Ca2+ levels in lymphocytes is through store-operated calcium entry (SOCE) and calcium-release-activated calcium (CRAC) channels. This Review focuses on the role of Ca2+ signals in lymphocyte functions, the signalling pathways leading to Ca2+ influx, the function of the recently discovered regulators of Ca2+ influx (STIM and ORAI), and the relationship between Ca2+ signals and diseases of the immune system.

TLR stimulation modifies BLyS receptor expression in follicular and marginal zone B cells

Through their differential interactions with B lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL), the three BLyS family receptors play central roles in B cell survival and differentiation. Recent evidence indicates BLyS receptor levels shift following BCR ligation, suggesting that activation cues can alter overall BLyS receptor profiles and thus ligand sensitivity. In this study, we show that TLR stimuli also alter BLyS receptor expression, but in contrast to BCR ligation, TLR9 and TLR4 signals, preferentially increase transmembrane activator calcium modulator and cyclophilin ligand interactor (TACI) expression. Although both of these TLRs act through MyD88-dependent mechanisms to increase TACI expression, they differ in terms of their downstream mediators and the B cell subset affected. Surprisingly, only TLR4 relies on c-Rel and p50 to augment TACI expression, whereas TLR9 does not. Furthermore, although all follicular and marginal zone B cells up-regulate TACI in response to TLR9 stimulation, only marginal zone B cells and a subset of follicular B cells respond to TLR4. Finally, we find that both BLyS and APRIL enhance viability among quiescent and BCR-stimulated B cells. However, although BLyS enhances viability among TLR stimulated B cells, APRIL does not, suggesting that TACI but not BLyS receptor 3 may share survival promoting pathways with TLRs.