Common variable immunodeficiency at the end of a prospering decade: towards novel gene defects and beyond

Peripheral blood monocyte and T cell subsets in children with specific polysaccharide antibody deficiency (SPAD)

Specific polysaccharide antibody deficiency (SPAD) is a well reported immunodeficiency characterized by a failure to produce antibodies against polyvalent polysaccharide antigens, expressed by encapsulated microorganisms. The clinical presentation of these patients involves recurrent bacterial infections, being the most frequent agent Streptococcus (S.) pneumoniae. In SPAD patients few reports refer to cells other than B cells. Since the immune response to S. pneumoniae and other encapsulated bacteria was historically considered restricted to B cells, the antibody deficiency seemed enough to justify the repetitive infections in SPAD patients. Our purpose is to determine if the B cell defects reported in SPAD patients are accompanied by defects in other leukocyte subpopulations necessary for the development of a proper adaptive immune response against S. pneumoniae. We here report that age related changes observed in healthy children involving increased percentages of classical monocytes (CD14++ CD16- cells) and decreased intermediate monocytes (CD14++ CD16+ cells), are absent in SPAD patients. Alterations can also be observed in T cells, supporting that the immune deficiency in SPAD patients is more complex than what has been described up to now.

Dysregulated extracellular signal-regulated kinase signaling associated with impaired B-cell receptor endocytosis in patients with common variable immunodeficiency

BACKGROUND

Common variable immunodeficiency (CVID) is a heterogeneous disorder characterized by B-cell dysfunction and, in a subgroup, by expansion of CD21(low) B cells. The CD21(low) B cells display defects in early B-cell receptor (BCR) signaling resembling those of anergic B cells.

OBJECTIVE

We sought to investigate whether B cells from patients with CVID, like anergic B cells, have defects in extracellular signal-regulated kinase (ERK) phosphorylation and in endocytic trafficking of the BCR.

METHODS

Using flow cytometry, we evaluated phosphorylated ERK (pERK) expression and internalization of cross-linked BCR in B-cell subsets. The localization of internalized BCR to lysosome-associated membrane protein 1-positive late endosomes was evaluated with confocal microscopy.

RESULTS

Constitutive pERK levels were increased in naive and IgM(+) memory B cells of patients with CVID compared with those of healthy donors, whereas the pERK increment induced by BCR cross-linking was relatively reduced. Intravenous immunoglobulin administration enhanced these anomalies, but they appeared to be intrinsic to B cells from patients with CVID. Cross-linking-induced BCR endocytosis was decreased in the IgM(+) memory B cells, especially in those with a CD21(low) phenotype, but not in the naive B cells of patients with CVID with CD21(low) expansion. Internalized BCR localized normally to late endosomes. Pharmacologic inhibition of ERK phosphorylation suppressed BCR endocytosis in B cells of healthy patients and those with CVID.

CONCLUSIONS

The B cells of patients with CVID with CD21(low) B-cell expansion resemble anergic B cells based on high constitutive pERK expression. The IgM(+) memory B cells of these patients, especially those that are CD21(low), have a defect in BCR endocytosis seemingly caused by dysregulated ERK signaling.

[Common variable immunodeficiency: a clinical challenge]

Common variable immunodeficiency (CVID) represents the most common clinically relevant form of primary immunodeficiency. This heterogeneous antibody deficiency syndrome is characterized not only by susceptibility to bacterial respiratory tract infections but displays additional signs of immune dysregulation, such as autoimmunity, chronic inflammation and lymphoproliferation in more than 30 % of the patients. Due to poor awareness the diagnosis is often delayed by 4-6 years. A close collaboration in patient care with a center specialized in primary immunodeficiency is recommended. Regular follow-up visits include assessment of adequate immunoglobulin replacement therapy and screening for manifestation of secondary complications. Regular substitution with intravenous or subcutaneous immunoglobulins has more or less normalized life expectancy of patients with isolated susceptibility to bacterial infections. Therefore, the current core task in the management of CVID patients is the elaboration of more effective and safer forms of prophylaxis and treatment of sequelae of immune dysregulation in the lungs, intestines and liver of affected patients.

B-lymphocyte lineage cells and the respiratory system

Adaptive humoral immune responses in the airways are mediated by B cells and plasma cells that express highly evolved and specific receptors and produce immunoglobulins of most isotypes. In some cases, such as autoimmune diseases or inflammatory diseases caused by excessive exposure to foreign antigens, these same immune cells can cause disease by virtue of overly vigorous responses. This review discusses the generation, differentiation, signaling, activation, and recruitment pathways of B cells and plasma cells, with special emphasis on unique characteristics of subsets of these cells functioning within the respiratory system. The primary sensitization events that generate B cells responsible for effector responses throughout the airways usually occur in the upper airways, tonsils, and adenoid structures that make up the Waldeyer ring. On secondary exposure to antigen in the airways, antigen-processing dendritic cells migrate into secondary lymphoid organs, such as lymph nodes, that drain the upper and lower airways, and further B-cell expansion takes place at those sites. Antigen exposure in the upper or lower airways can also drive expansion of B-lineage cells in the airway mucosal tissue and lead to the formation of inducible lymphoid follicles or aggregates that can mediate local immunity or disease.

Dependence of immunoglobulin class switch recombination in B cells on vesicular release of ATP and CD73 ectonucleotidase activity

Immunoglobulin (Ig) isotype diversification by class switch recombination (CSR) is an essential process for mounting a protective humoral immune response. Ig CSR deficiencies in humans can result from an intrinsic B cell defect; however, most of these deficiencies are still molecularly undefined and diagnosed as common variable immunodeficiency (CVID). Here, we show that extracellular adenosine critically contributes to CSR in human naive and IgM memory B cells. In these cells, coordinate stimulation of B cell receptor and toll-like receptors results in the release of ATP stored in Ca(2+)-sensitive secretory vesicles. Plasma membrane ectonucleoside triphosphate diphosphohydrolase 1 CD39 and ecto-5'-nucleotidase CD73 hydrolyze ATP to adenosine, which induces CSR in B cells in an autonomous fashion. Notably, CVID patients with impaired class-switched antibody responses are selectively deficient in CD73 expression in B cells, suggesting that CD73-dependent adenosine generation contributes to the pathogenesis of this disease.

Multiplex B cell characterization in blood, lymph nodes, and tumors from patients with malignancies

B lymphocytes contribute to immune surveillance, by tumor-specific Abs and Ag presentation to T lymphocytes, but are insufficiently studied in humans. In this article, we report a flow cytometric investigation of B lymphocyte subpopulations in blood, lymph nodes (LNs), and malignant tissues from 20 patients operated on because of advanced solid tumors. The CD19(+) compartment in peripheral blood was essentially unaltered in patients, as compared with healthy control subjects. In metastatic LNs, signs of B lymphocyte activation were observed, as evidenced by increased proportions of plasmablasts and CD86-expressing cells. In tumor-infiltrating B lymphocytes (TIL-B), both switched memory cells and plasmablasts were expanded, as compared with nonmalignant epithelium. Moreover, pronounced skewing of Igλ/Igκ ratio was evident among TIL-Bs. By spectratype analysis on IgH, we confirmed a monoclonal expansion of the Vh7 family in TIL-B, also present in a tumor-associated LN. Sequencing the clonally expanded Vh7 revealed signs of somatic hypermutation. In conclusion, B lymphocytes in cancer patients exhibit signs of activation in tumor-associated tissues, likely induced by recognition of tumor Ags. Increased numbers of switched memory cells and plasmablasts in combination with clonal expansion and signs of somatic hypermutation suggest a CD4(+) T lymphocyte-dependent antitumoral response, which may be exploited for immunotherapy.

An update on clinical immunology, immune mechanisms and deficiency diseases

29th Annual Jackson Hole, Wyoming, Update in Clinical Immunology, Microbiology and Infectious Diseases Salt Lake city, UT, USA, 9-13 July 2012 The 29th Annual Jackson Hole, Wyoming, Update in Clinical Immunology, Microbiology and Infectious Diseases was held from 9 to 13 July 2012. This postgraduate, continuing medical education course of the University of Utah's Department of Pathology (UT, USA) is designed for laboratorians, clinical pathologists, pathologists, clinicians, clinical immunology and infectious disease specialists and medical technologists, as well as residents and fellows training in immunology, microbiology or infectious diseases.

Sequence variants of the TNFRSF13B gene in Czech CVID and IgAD patients in the context of other populations

Mutations in the TNFRSF13B gene, encoding TACI, have been found in common variable immunodeficiency (CVID) and selective IgA deficient (IgAD) patients, but only the association with CVID seems to be significant. In this study, Czech CVID, IgAD and primary hypo/dysgammaglobulinemic (HG/DG) patients were screened for all TNFRSF13B sequence variants. The TNFRSF13B gene was mutated in 4/70 CVID patients (5.7%), 9/161 IgAD patients (5.6%), 1/17 HG/DG patient (5.9%) and none of 195 controls. Eight different mutations were detected, including the most frequent p.C104R and p.A181E mutations as well as 1 novel missense mutation, p.R189K. A significant association of TNFRSF13B gene mutations was observed in both CVID (p=0.01) and IgAD (p=0.002) Czech patients. However, when combined with all published data, only the association with CVID remained significant compared with the controls (9.9% vs. 3.2%, p<10(-6)), while statistical significance disappeared for IgAD (5.7% vs. 3.2%, p=0.145). The silent mutation p.P97P was shown to be associated significantly with CVID compared with the controls in both Czech patients (allele frequency 4.3% vs. 0.2%, p=0.01) and in connection with the published data (5.1% vs. 1.8%, p=0.003). The relevance of some TNFRSF13B gene variants remains unclear and needs to be elucidated in future studies.

Autoimmune cytopenias in common variable immunodeficiency

Common variable immunodeficiency (CVID) is a humoral immunodeficiency whose primary diagnostic features include hypogammaglobulinemia involving two or more immunoglobulin isotypes and impaired functional antibody responses in the majority of patients. While increased susceptibility to respiratory and other infections is a common thread that binds a large cross-section of CVID patients, the presence of autoimmune complications in this immunologically and clinically heterogeneous disorder is recognized in up to two-thirds of patients. Among the autoimmune manifestations reported in CVID (20–50%; Chapel et al., 2008; Cunningham-Rundles, 2008), autoimmune cytopenias are by far the most common occurring variably in 4–20% (Michel et al., 2004; Chapel et al., 2008) of these patients who have some form of autoimmunity. Association of autoimmune cytopenias with granulomatous disease and splenomegaly has been reported. The spectrum of autoimmune cytopenias includes thrombocytopenia, anemia, and neutropenia. While it may seem paradoxical “prima facie” that autoimmunity is present in patients with primary immune deficiencies, in reality, it could be considered two sides of the same coin, each reflecting a different but inter-connected facet of immune dysregulation. The expansion of CD21 low B cells in CVID patients with autoimmune cytopenias and other autoimmune features has also been previously reported. It has been demonstrated that this unique subset of B cells is enriched for autoreactive germline antibodies. Further, a correlation has been observed between various B cell subsets, such as class-switched memory B cells and plasmablasts, and autoimmunity in CVID. This review attempts to explore the most recent concepts and highlights, along with treatment of autoimmune hematological manifestations of CVID.

DNA repair: the link between primary immunodeficiency and cancer

The adaptive component of the immune system depends greatly on the generation of genetic diversity provided by lymphocyte-specific genomic rearrangements. V(D)J recombination, class switch recombination (CSR), and somatic hypermutation (SHM) constitute complex and vulnerable processes that are orchestrated by a multitude of DNA repair pathways. When inherited defects in certain DNA repair proteins are present, lymphocyte development can be compromised and, consequently, patients can develop primary immunodeficiencies (PIDs). PID patients often have a strong predisposition for cancer development as a result of genomic instability generated from defective DNA repair mechanisms. Tumors of lymphoid origin are one of the most common PID-associated cancers, likely due to DNA lesions resulting from defective V(D)J, CSR, and SHM. In this review, we describe PID syndromes that confer an increased risk for cancer development. Furthermore, we discuss the role of the affected proteins in tumorigenesis/lymphomagenesis.

Parental consanguinity is associated with a severe phenotype in common variable immunodeficiency

The DEFI study has collected clinical data and biological specimens from kindreds with CVID. Patients with demonstrated parental consanguinity (cCVID group) were compared to patients without parental consanguinity (ncCVID). A total of 24 of the 436 patients with CVID had consanguineous parents. Age at first symptoms and age at diagnosis were comparable in the two groups. Some complications were more frequent in cCVID patients: splenomegaly (62.5% vs. 29%; p = 0.001), granulomatous disease (29% vs. 12%; p = 0.02), and bronchiectasis (58% vs. 29%; p = 0.003). A high incidence of opportunistic infections was also observed in this population (29% vs. 5%; p < 0.001). Distribution of B-cell subsets were similar in the two groups. Naïve CD4+ T cells were decreased in cCVID patients (15% vs. 28%; p < 0.001), while activated CD4 + CD95+ (88% vs. 74%; p = 0.002) and CD8 + HLA-DR + T cells (47% vs. 31%; p < 0.001) were increased in these patients when compared to ncCVID patients. Parental consanguinity is associated with an increased risk of developing severe clinical complications in patients with CVID. Most of these patients presented with severe T-cell abnormalities and should be considered with a diagnosis of late-onset combined immune deficiency (LOCID). Systematic investigation for parental consanguinity in patients with CVID provides useful information for specific clinical care and genetic screening.

IgG placental transfer in healthy and pathological pregnancies

Placental transfer of maternal IgG antibodies to the fetus is an important mechanism that provides protection to the infant while his/her humoral response is inefficient. IgG is the only antibody class that significantly crosses the human placenta. This crossing is mediated by FcRn expressed on syncytiotrophoblast cells. There is evidence that IgG transfer depends on the following: (i) maternal levels of total IgG and specific antibodies, (ii) gestational age, (iii) placental integrity, (iv) IgG subclass, and (v) nature of antigen, being more intense for thymus-dependent ones. These features represent the basis for maternal immunization strategies aimed at protecting newborns against neonatal and infantile infectious diseases. In some situations, such as mothers with primary immunodeficiencies, exogenous IgG acquired by intravenous immunoglobulin therapy crosses the placenta in similar patterns to endogenous immunoglobulins and may also protect the offspring from infections in early life. Inversely, harmful autoantibodies may cross the placenta and cause transitory autoimmune disease in the neonate.

Novel sequencing-based strategies for high-throughput discovery of genetic mutations underlying inherited antibody deficiency disorders

Human inherited antibody deficiency disorders are generally caused by mutations in genes involved in the pathways regulating B-cell class switch recombination; DNA damage repair; and B-cell development, differentiation, and survival. Sequencing a large set of candidate genes involved in these pathways appears to be a highly efficient way to identify novel mutations. Herein we review several high-throughput sequencing approaches as well as recent improvements in target gene enrichment technologies. Systematic improvement of enrichment and sequencing methods, along with refinement of the experimental process is necessary to develop a cost-effective high-throughput resequencing assay for a large cohort of patient samples. The Hyper-IgM/CVID chip is one example of a resequencing platform that may be used to identify known or novel mutations in patents with various types of inherited antibody deficiency.