An antibody-deficiency syndrome due to mutations in the CD19 gene

Transmembrane activator and calcium-modulator and cyclophilin ligand interactor mutations in common variable immunodeficiency

PURPOSE OF REVIEW

TNFRSF13B, the gene which encodes transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI), is mutated in nearly 10% of patients with common variable immune deficiency (CVID), an antibody deficiency syndrome characterized by loss of memory B cells and plasma cells. This review discusses the normal function of TACI and the role of TACI mutants in CVID.

RECENT FINDINGS

TACI activates isotype switching, mediates immunoglobulin production in response to type II T-independent antigens, and plays an inhibitory role in B cell homeostasis. Recent evidence indicates that TACI synergizes with CD40 and Toll-like receptors for immunoglobulin secretion and promotion of plasma cell differentiation. The two most common TACI mutants associated with CVID--C104R and A181E--are primarily found as heterozygous mutations suggesting that they either cause haploinsufficiency or exert a dominant negative effect. TACI mutations in CVID are associated with an increased susceptibility to autoimmunity and lymphoproliferation.

SUMMARY

TACI has a dual function in promoting B cell antibody responses and inhibiting B cell proliferation. The observation that TACI mutations are present in healthy participants suggests that modifier genes may play an important role in the development of CVID. The discovery of these genes will help understand the pathogenesis of this disease.

[Late onset of primary immune deficiencies]

Primary immune deficiencies (PID) are characterized by a failure of the immune system that is not explained by any infectious, neoplastic, or iatrogenic cause. The diagnosis of PID should be considered in cases of severe or recurrent infections but also in cases with granulomatosis, autoimmune diseases, hemophagocytic syndrome, lymphoproliferative disorders, or even some solid tumors. The onset of PID may be late, most often in adulthood. Nonetheless, late onset may also mean in the first years rather than months of life or in adolescence rather than early childhood. In adults, the diagnosis of PID cannot be considered before acquired immunodeficiencies--far more frequent--are ruled out. Factors affecting the late onset of PID are not known.

Update in understanding common variable immunodeficiency disorders (CVIDs) and the management of patients with these conditions

The common variable immunodeficiency disorders are a mixed group of heterogeneous conditions linked by lack of immunoglobulin production and primary antibody failure. This variability results in difficulty in making coherent sense of either immunopathogenesis or the role of various genetic abnormalities reported in the literature. The recent attempt to collate the varied complications in these conditions and to define particular clinical phenotypes has improved our understanding of these diseases. Once refined and confirmed by other studies, these definitions will facilitate improved accuracy of prognosis and better management of clinical complication. They may also provide a method of analysing outcomes as related to new immunopathological and genetic findings.

Common variable immunodeficiency

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

TACI mutations and disease susceptibility in patients with common variable immunodeficiency

The most prevalent primary immunodeficiency is common variable immunodeficiency (CVID). Mutations have been described in four genes, ICOS, CD19, BAFF-R and TNFRSF13B (encoding TACI), together associated with 10-15% of CVID cases. We investigated a family with CVID and identified the heterozygous C104R TNFRSF13B mutation in two of the three index-children with CVID, a mother with selective immunoglobulin A deficiency, a mother with recurrent infections and a healthy grandfather. Remarkably, we did not find the TNFRSF13B mutation in the third index-child with CVID, despite his hypogammaglobulinaemia and decreased response to unconjugated pneumococcal vaccine. This family illustrates that TNFRSF13B mutations induce disease susceptibility rather than cause disease directly. Apparently, other genetic or environmental factors, still to be identified, contributed to the development of CVID in this family. Consequently, TNFRSF13B mutations must be interpreted with caution in the clinical setting.

Primary B cell immunodeficiencies: comparisons and contrasts

Sophisticated genetic tools have made possible the identification of the genes responsible for most well-described immunodeficiencies in the past 15 years. Mutations in Btk, components of the pre-B cell and B cell receptor (lambda5, Igalpha, Igbeta), or the scaffold protein BLNK account for approximately 90% of patients with defects in early B cell development. Hyper-IgM syndromes result from mutations in CD40 ligand, CD40, AID, or UNG in 70-80% of affected patients. Rare defects in ICOS or CD19 can result in a clinical picture that is consistent with common variable immunodeficiency, and as many as 10% of patients with this disorder have heterozygous amino acid substitutions in TACI. For all these disorders, there is considerable clinical heterogeneity in patients with the same mutation. Identifying the genetic and environmental factors that influence the clinical phenotype may enhance patient care and our understanding of normal B cell development.

Relevance of biallelic versus monoallelic TNFRSF13B mutations in distinguishing disease-causing from risk-increasing TNFRSF13B variants in antibody deficiency syndromes

TNFRSF13B encodes transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), a B cell- specific tumor necrosis factor (TNF) receptor superfamily member. Both biallelic and monoallelic TNFRSF13B mutations were identified in patients with common variable immunodeficiency disorders. The genetic complexity and variable clinical presentation of TACI deficiency prompted us to evaluate the genetic, immunologic, and clinical condition in 50 individuals with TNFRSF13B alterations, following screening of 564 unrelated patients with hypogammaglobulinemia. We identified 13 new sequence variants. The most frequent TNFRSF13B variants (C104R and A181E; n=39; 6.9%) were also present in a heterozygous state in 2% of 675 controls. All patients with biallelic mutations had hypogammaglobulinemia and nearly all showed impaired binding to a proliferation-inducing ligand (APRIL). However, the majority (n=41; 82%) of the pa-tients carried monoallelic changes in TNFRSF13B. Presence of a heterozygous mutation was associated with antibody deficiency (P< .001, relative risk 3.6). Heterozygosity for the most common mutation, C104R, was associated with disease (P< .001, relative risk 4.2). Furthermore, heterozygosity for C104R was associated with low numbers of IgD(-)CD27(+) B cells (P= .019), benign lymphoproliferation (P< .001), and autoimmune complications (P= .001). These associations indicate that C104R heterozygosity increases the risk for common variable immunodeficiency disorders and influences clinical presentation.

Hypogammaglobulinaemia

This article reviews the primary immunodeficiencies that result in hypogammaglobulinemia or predominantly antibody deficiency disorders. This group makes up the largest proportion of patients with primary immunodeficiency. Significant advances have been made in understanding the molecular basis and clinical characteristics of patients with the more severe forms of antibody deficiency in the last 6 years. Recognition of these disorders remains poor with significant diagnostic delay. The milder forms of antibody deficiency disorders, especially those with normal total serum immunoglobulin G levels, remain poorly characterized and understood. Further work remains to be done in understanding and recognizing these syndromes to benefit patient care and foster further knowledge of the immune system.

Primary antibody deficiency syndromes

The primary antibody deficiency syndromes are a group of rare disorders characterized by an inability to produce clinically effective immunoglobulin responses. Some of these disorders result from genetic mutations in genes involved in B cell development, whereas others appear to be complex polygenic disorders. They most commonly present with recurrent infections due to encapsulated bacteria, although in the most common antibody deficiency, Common Variable Immunodeficiency, systemic and organ-specific autoimmunity can be a presenting feature. Diagnostic delay in this group of disorders remains a problem, and the laboratory has a vital role in the detection of abnormalities in immunoglobulin concentration and function. It is critical to distinguish this group of disorders from secondary causes of hypogammaglobulinaemia, in particular lymphoid malignancy, and appropriate laboratory investigations are of critical importance. Treatment of primary antibody deficiencies involves immunoglobulin replacement therapy, either via the intravenous or subcutaneous route. Patients remain at risk of a wide variety of complications, not all linked to diagnostic delay and inadequate therapy. In common variable immunodeficiency (CVID) in particular, patients remain at significantly increased risk of lymphoid malignancy, and regular clinical and laboratory monitoring is required. This review aims to give an overview of these conditions for the general reader, covering pathogenesis, clinical presentation, laboratory investigation, therapy and clinical management.

Clinical heterogeneity can hamper the diagnosis of patients with ZAP70 deficiency

One of the severe combined immunodeficiencies (SCIDs), which is caused by a genetic defect in the signal transduction pathways involved in T-cell activation, is the ZAP70 deficiency. Mutations in ZAP70 lead to both abnormal thymic development and defective T-cell receptor (TCR) signaling of peripheral T-cells. In contrast to the lymphopenia in most SCID patients, ZAP70-deficient patients have lymphocytosis, despite the selective absence of CD8+ T-cells. The clinical presentation is usually before 2 years of age with typical findings of SCID. Here, we present three new ZAP70-deficient patients who vary in their clinical presentation. One of the ZAP70-deficient patients presented as a classical SCID, the second patient presented as a healthy looking wheezy infant, whereas the third patient came to clinical attention for the eczematous skin lesions simulating atopic dermatitis with eosinophilia and elevated immunoglobulin E (IgE), similar to the Omenn syndrome. This study illustrates that awareness of the clinical heterogeneity of ZAP70 deficiency is of utmost importance for making a fast and accurate diagnosis, which will contribute to the improvement of the adequate treatment of this severe immunodeficiency.

Flowcytometric phenotyping of common variable immunodeficiency

BACKGROUND

Common variable immunodeficiency (CVID) comprises heterogeneous antibody deficiency disorders. To classify this heterogeneous syndrome, clinical as well as immunologic parameters have been combined. Flowcytometric analysis of circulating T and B lymphocyte subpopulations has become an important tool in this endeavor of disease classification.

METHODS

Multicolor flowcytometric analysis of circulating lymphocytes.

RESULTS

The flowcytometric analysis of B and T cell subpopulations in the blood of CVID patients has contributed significantly to the identification of separate groups within the CVID population. In addition, the flowcytometric analysis of the inducible costimulator on activated T cells, CD19 and BAFF-R on B cells are valid screening methods for three of the four known genetic defects associated with CVID. Only TACI deficiency can not be sufficiently detected by flowcytometric measures.

CONCLUSIONS

Flowcytometric classification of patients with CVID has become a standard procedure during the diagnostic work up. This should be performed according to common guidelines to guarantee world wide comparability between different immunodeficiency centers.

Memory B cells in common variable immunodeficiency: clinical associations and sex differences

Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by impaired antibody responses, recurrent infections, inflammatory, autoimmune and malignancy-related conditions. We evaluated the relationship between memory B cell phenotype, sex, age at diagnosis, immunologic and clinical conditions in 105 CVID subjects from one medical center. Reduced numbers of switched memory B cells (cutoff Collapse

Key Words

• cvid
• igm memory b cells
• switched memory b cells
• pneumococcal antibody
• sex differences
• igg
• splenectomy

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MESH Headings

• Adolescent
• Adult
• Aged
• Aged, 80 and over
• Antibodies/blood
• Autoimmunity
• B-Lymphocyte Subsets/immunology
• B-Lymphocyte Subsets/metabolism
• Child
• Child, Preschool
• Common Variable Immunodeficiency/immunology
• Common Variable Immunodeficiency/metabolism
• Common Variable Immunodeficiency/surgery
• Female
• Humans
• Immunoglobulin A/blood
• Immunoglobulin G/blood
• Immunologic Memory
• Immunophenotyping
• Male
• Middle Aged
• Pneumococcal Vaccines/immunology
• Pneumococcal Vaccines/metabolism
• Sex Characteristics
• Splenectomy
• Splenomegaly/immunology

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Grants

• AI 101093 NIAID NIH HHS
• P01 AI061093 NIAID NIH HHS
• R18 AI048693 NIAID NIH HHS
• AI-467320 NIAID NIH HHS
• AI-48693 NIAID NIH HHS
• R21 AI101093 NIAID NIH HHS

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Affiliation(s)

Silvia Sánchez-Ramón Department of Medicine, Pediatrics and Immunobiology Center, Mount Sinai Medical School, New York, NY, USA Clinical Immunology Unit, Department of Immunology, General University Hospital Gregorio Marañón, Madrid, Spain
Lin Radigan Department of Medicine, Pediatrics and Immunobiology Center, Mount Sinai Medical School, New York, NY, USA
Joyce E. Yu Department of Medicine, Pediatrics and Immunobiology Center, Mount Sinai Medical School, New York, NY, USA
Susan Bard Department of Medicine, Pediatrics and Immunobiology Center, Mount Sinai Medical School, New York, NY, USA
Charlotte Cunningham-Rundles Department of Medicine, Pediatrics and Immunobiology Center, Mount Sinai Medical School, New York, NY, USA

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Collaborators Collapse

Common variable immunodeficiency: a new look at an old disease

Primary immunodeficiencies comprise many diseases caused by genetic defects primarily affecting the immune system. About 150 such diseases have been identified with more than 120 associated genetic defects. Although primary immunodeficiencies are quite rare in incidence, the prevalence can range from one in 500 to one in 500 000 in the general population, depending on the diagnostic skills and medical resources available in different countries. Common variable immunodeficiency (CVID) is the primary immunodeficiency most commonly encountered in clinical practice, and appropriate diagnosis and management of patients will have a significant effect on morbidity and mortality as well as financial aspects of health care. Advances in diagnostic laboratory methods, including B-cell subset analysis and genetic testing, coupled with new insights into the molecular basis of immune dysfunction in some patients with CVID, have enabled advances in the clinical classification of this heterogeneous disease.

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.

Lymphoma in common variable immunodeficiency: interplay between immune dysregulation, infection and genetics

PURPOSE OF REVIEW

Common variable immunodeficiency represents the largest group of primary immunodeficiency patients. The variable clinical manifestations include an increased susceptibility to chronic infections, granulomatous disease and the lymphoproliferative predisposition to develop lymphoma. This review discusses the latest insights into common variable immunodeficiency and uses common variable immunodeficiency as a model to examine the links between immunodeficiency and chronic infections in causing lymphoma.

RECENT FINDINGS

Newly identified disease genes within the common variable immunodeficiency population, have advanced the understanding of human immunodeficiency and the molecular basis of B-cell biology. Refined laboratory techniques have better defined this heterogeneous condition by classifying the underlying B-cell and T-cell abnormalities. New sensitive methods have also identified the presence of persistent infections that may play a role in the development of lymphoma.

SUMMARY

There are several reasons for an increased risk of lymphoma in common variable immunodeficiency patients. These include genetics, immune dysregulation, radiosensitivity and chronic infections such as Helicobacter pylori, human herpes virus type 8 and cytomegalovirus. Chronic infections may enhance the development of lymphoma in an antigen specific manner. The interaction between chronic infections and the development of lymphoma is still unclear but studies to clarify this may lead to prevention measures and lymphoma reduction strategies.

B-cell maturation defects in common variable immunodeficiency and association with clinical features

AIMS

Patients with common variable immunodeficiency (CVID) often have defects in post-antigenic B-cell differentiation with fewer memory B cells and impaired isotype switching. We aimed to classify CVID patients according to these defects and determine whether this predicted clinical manifestations.

METHODS

We analysed the memory marker CD27, maturation marker CD21, and IgD on peripheral blood B cells from 31 CVID patients and 23 controls using a whole-blood lysis technique, allocated patients according to two classifications ('Freiburg' and 'Paris') and correlated results with clinical manifestations.

RESULTS

CVID patients had fewer memory (CD27(+)) B cells and isotype-switched (IgD(-)) memory B cells in absolute number and proportion. Many CVID patients had increased immature (CD21(-)) B cells. Lymphoproliferation and autoimmune cytopenias were found almost exclusively in these patients, including Freiburg group Ia (decreased switched memory and increased immature B cells), but also those with normal switched memory and increased immature B cells. The Paris classification was less useful in predicting clinical manifestations.

CONCLUSIONS

CVID is associated with defects in memory B-cell differentiation. Subclassification helps identify patients with clinical manifestations, particularly lymphoproliferation and autoimmune cytopenias in those with impaired B-cell maturation and isotype switching. Routine B-cell phenotyping may assist clinicians in predicting these clinical features.

Infections in 252 patients with common variable immunodeficiency

BACKGROUND

Common variable immunodeficiency is characterized by recurrent infections and defective immunoglobulin production.

METHODS

The DEFI French national study prospectively enrolled adult patients with primary hypogammaglobulinemia. Clinical events before inclusion were retrospectively analyzed at that time.

RESULTS

From April 2004 through April 2007, 341 patients were enrolled, 252 of whom had received a diagnosis of common variable immunodeficiency; of those, 110 were male, 142 were female, and 228 were white. The median age at first symptoms was 19 years. The median age at common variable immunodeficiency diagnosis was 33.9 years. The median delay for diagnosis was 15.6 years for the 138 patients with initial symptoms before 1990 and 2.9 years for the 114 patients with initial symptoms from 1990 to the time of the study. The most frequent initial symptoms were upper respiratory tract infections: bronchitis (in 38% of patients), sinusitis (36%), pneumonia (31%), and/or bronchiectasis (14%). Overall, 240 patients had respiratory symptoms. Pneumonia was reported in 147 patients; Streptococcus pneumoniae and Haemophilus influenzae were documented in 46 and 17 cases, respectively. Recurrent or chronic diarrhea was reported in 118 patients. Giardia (35 cases), Salmonella (19), and Campylobacter (19) infections were more frequent in patients with undetectable serum immunoglobulin A (P<.001). Sixteen patients developed opportunistic infections. Persistent infections and requirement for antibiotics despite immunoglobulin substitution correlated with severe defect of memory switched B cells (P=.003) but not with immunoglobulin G trough levels (P=.55).

CONCLUSION

Although reduced within the past decade, the delay of diagnosis of common variable immunodeficiency remains unacceptable. Recurrence of upper respiratory tract infection or pneumonia should lead to systematic evaluation of serum immunoglobulin.

Antibody deficiency diseases

Primary immunodeficiency diseases are rare disorders characterized by quantitative or qualitative defects in cells or components in the immune system, resulting in a high degree of susceptibility to various types of infections. During differentiation, stem cells undergo a series of discrete steps, governed by a large number of different genes. Mutations/deletions in these genes will result in a block in differentiation of the affected cell lineage(s), leading to immunodeficiency. To date, more than 150 different types of disorders have been described. In this review, we will focus on novel findings in antibody deficiency syndromes.

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.

Screening of functional and positional candidate genes in families with common variable immunodeficiency

Background

Common variable immunodeficiency (CVID) comprises a heterogeneous group of primary antibody deficiencies with complex clinical and immunological phenotypes. The recent discovery that some CVID patients show monogenic defects in the genes encoding ICOS, TACI or CD19 prompted us to investigate several functional candidate genes in individuals with CVID.

Results

The exonic, protein coding regions of the genes encoding: APRIL, BCMA, IL10, IL10Rα, IL10Rβ, IL21, IL21R, and CCL18, were analyzed primarily in familial CVID cases, who showed evidence of genetic linkage to the respective candidate gene loci and CVID families with a recessive pattern of inheritance. Two novel SNPs were identified in exon 5 and exon 8 of the IL21R gene, which segregated with the disease phenotype in one CVID family. Eleven additional SNPs in the genes encoding BCMA, APRIL, IL10, IL10Rα, IL21 and IL21R were observed at similar frequencies as in healthy donors.

Conclusion

We were unable to identify obvious disease causing mutations in the protein coding regions of the analyzed genes in the studied cohort.

Common variable immunodeficiency

Common variable immunodeficiency (CVID) is a primary immunodeficiency that is characterized by low level of serum immunoglobulins and an increased susceptibility to infections. The patients show a variety of clinical, cellular, and immunological defects, may develop autoimmune disease, and are susceptible to malignancy. The recent identification of four genetic defects that result in the CVID phenotype demonstrates that the genetic basis of CVID is highly variable. The responsible gene products include, ICOS, TACI, BAFF-R, CD19. Insufficiency of each molecule disrupts B cell maturation, function and differentiation at a different stage. Despite the elucidation of responsible genes, the molecular mechanisms leading to the immune defects are still yet to be understood. In this paper, we overview the molecular basis of CVID, and will provide some data on how the defect leads to autoimmunity.

Common variable immune deficiency: reviews, continued puzzles, and a new registry

BACKGROUND

Common variable immune deficiency (CVID) is a clinically and immunologically heterogenous primary immune deficiency first described more than 50 years ago. The main features are hypogammaglobulinemia, recurrent infections, and other complications. While CVID is considered as a genetic immune defect, and several genes have been reported as leading to the CVID phenotype, one of the most puzzling features of CVID is the sporadic inheritance pattern and the relatively late onset. In most cases, no other family members have any immune defect. The mean age at diagnosis is between 25 and 45 years of age. These features suggest the interplay between either several or numerous genes with or without potential environmental factors.

Analysis of genetic defects in patients with the common variable immunodeficiency phenotype in a single Taiwanese tertiary care hospital

BACKGROUND

Seven known genetic defects, including Bruton tyrosine kinase (Btk), CD4OL, and signaling lymphocyte activation molecule-associated protein (SAP) (all X-linked) and inducible costimulator molecule (ICOS), transmembrane activator and calcium-modulator and cytophilin ligand interactor (TACI), B-cell-activating factor of the tumor necrosis family receptor (BAFFR), and CD19 (all autosomal recessive), were found in patients with the phenotype of common variable immunodeficiency (CVID).

OBJECTIVE

To investigate these 7 candidate protein expressions and candidate gene sequences for comprehensive analysis of known genetic defects in patients with CVID.

METHODS

These 7 candidate protein expressions were evaluated by flow cytometry or Western blot, and candidate genes were evaluated by direct sequencing.

RESULTS

Of 9 CVID patients from a single Taiwanese tertiary care hospital, we identified 2 cousins with decreased Btk expression who had a mutated (Asp521Val) kinase domain of Btk (1694A>T in exon 15) and 1 patient with decreased CD40L expression who had a mutated (Thr254Met) extracellular domain of CD40L (782T>C in exon 5).

CONCLUSION

This comprehensive approach revealed that, in Taiwan, in some patients mild forms of X-linked agammaglobulinemia and hyper-IgM syndrome caused the CVID phenotype. No mutations of SAP, ICOS, TACI, BAFFR, and CD19 were identified in this study, although selection bias among the small study population and genetic variation may exist.

Novel mutations in a Japanese patient with CD19 deficiency

Common variable immunodeficiency (CVID) is a heterogeneous disorder characterized by recurrent bacterial infections, hypogammaglobulinemia and low to normal numbers of circulating B cells. Mutations in the ICOS, TACI and CD19 genes have recently been identified in <10% of CVID patients. We, herein, describe two novel CD19 gene disruptions in an 8-year-old Japanese boy, who had been clinically diagnosed as having CVID at the age of 5 years. Flow-cytometric analysis demonstrated absence of CD19 and reduced CD21 expression on CD20-postive peripheral blood B cells. Mutation analysis of CD19 revealed a mutation in the splice acceptor site of intron 5 (IVS5-1G>T) of the maternal allele, resulting in skipping of exon 6, and a truncated protein product. The paternal allele was disrupted by a gross deletion encompassing at least the ATP2A1, CD19 and NFATC2IP genes. The patient had a small number of IgD(-) CD27(+) memory B cells, in which somatic mutation were detected. His B cells showed substantial proliferation upon stimulation, but reduced IgG and IgA production in vitro. These findings extend the mutation spectrum of the CD19 deficiency to four, and confirm the homogeneity of the CD19 deficiency as a unique type of CVID.

Common variable immunodeficiency in children

PURPOSE OF REVIEW

Common variable immunodeficiency is the most common primary immunodeficiency that needs medical attention. Symptoms may occur at any time, with two major peaks of onset at 5-10 and 20-30 years. We present the different clinical phenotypes of common variable immunodeficiency, review recent genetic findings and point to current treatment strategies.

RECENT FINDINGS

Five genes, ICOS, CD19, TNFRSF13B, TNFRSF13C and MSH5, have been found to be mutated in patients with common variable immunodeficiency. Additional possible genetic loci for autosomal dominant forms were detected on chromosomes 4q and 16q. These findings illustrate the heterogeneous molecular basis of common variable immunodeficiency and indicate the value of genetic linkage studies, thereby improving the genetic diagnosis.

SUMMARY

In young patients with unusually frequent bacterial infections, common variable immunodeficiency should always be considered as a differential diagnosis. The compulsory individual work-up should comprise a family history in order to document siblings and additional family members suffering from common variable immunodeficiency and/or selective IgA deficiency. Since the recently found gene defects affect a minority of patients with common variable immunodeficiency only, future genetic research is required to identify further susceptibility genes involved in the pathogenesis of this condition.

Genetic causes of bronchiectasis: primary immune deficiencies and the lung

Primary immune deficiencies (PID) comprise a heterogeneous group of genetically determined disorders that affect development and/or function of innate or adaptive immunity. Consequently, patients with PID suffer from recurrent and/or severe infections that frequently involve the lung. While the nature of the immune defect often dictates the type of pathogens that may cause lung infection, there is substantial overlap of radiological findings, so that appropriate laboratory tests are mandatory to define the nature of the immune defect and to prompt appropriate treatment. At the same time, the recent identification of a large number of PID-causing genes now allows early, even presymptomatic diagnosis, thus representing an essential tool for prevention of lung damage. This review article describes the most common forms of PID, their cellular and molecular bases, and the associated lung abnormalities, and reports on available treatment.

Genetic defects in common variable immunodeficiency

Common variable immunodeficiency (CVID) is the most frequent clinically manifested primary immunodeficiency. According to clinical and laboratory findings, CVID is a heterogeneous group of diseases. Recently, the defects of molecules regulating activation and terminal differentiation of B lymphocytes have been described in some patients with CVID. In this study, we show the overview of deficiencies of inducible costimulator, transmembrane activator and calcium-modulator and cytophilin ligand interactor, CD19 molecules, their genetic basis, pathogenesis and clinical manifestations.

The EUROclass trial: defining subgroups in common variable immunodeficiency

The heterogeneity of common variable immunodeficiency (CVID) calls for a classification addressing pathogenic mechanisms as well as clinical relevance. This European multicenter trial was initiated to develop a consensus of 2 existing classification schemes based on flowcytometric B-cell phenotyping and the clinical course. The clinical evaluation of 303 patients with the established diagnosis of CVID demonstrated a significant coincidence of granulomatous disease, autoimmune cytopenia, and splenomegaly. Phenotyping of B-cell subpopulations confirmed a severe reduction of switched memory B cells in most of the patients that was associated with a higher risk for splenomegaly and granulomatous disease. An expansion of CD21(low) B cells marked patients with splenomegaly. Lymphadenopathy was significantly linked with transitional B-cell expansion. Based on these findings and pathogenic consideration of B-cell differentiation, we suggest an improved classification for CVID (EUROclass), separating patients with nearly absent B cells (less than 1%), severely reduced switched memory B cells (less than 2%), and expansion of transitional (more than 9%) or CD21(low) B cells (more than 10%). Whereas the first group contains all patients with severe defects of early B-cell differentiation, severely reduced switched memory B cells indicate a defective germinal center development as found in inducible constimulator (ICOS) or CD40L deficiency. The underlying defects of expanded transitional or CD21(low) B cells remain to be elucidated. This trial is re-gistered at http://www.uniklinik-freiburg.de/zks/live/uklregister/Oeffentlich.html as UKF000308.

Translational mini-review series on immunodeficiency: molecular defects in common variable immunodeficiency

Common variable immunodeficiency (CVID) is a primary immunodeficiency that typically affects adults and is characterized by abnormalities of quantative and qualitative humoral function that are heterogeneous in their immunological profile and clinical manifestations. The recent identification of four monogenic defects that result in the CVID phenotype also demonstrates that the genetic basis of CVID is highly variable. Mutations in the genes encoding the tumour necrosis factor (TNF) superfamily receptors transmembrane activator and calcium-modulating ligand interactor (TACI) and B cell activation factor of the TNF family receptor (BAFF-R), CD19 and the co-stimulatory molecule inducible co-stimulator molecule (ICOS) all lead to CVID and illustrate the complex interplay required to co-ordinate an effective humoral immune response. The molecular mechanisms leading to the immune defect are still not understood clearly and particularly in the case of TACI, where a number of heterozygous mutations have been found in affected individuals, the molecular pathogenesis of disease requires further elucidation. Together these defects account for perhaps 10-15% of all cases of CVID and it is highly likely that further genetic defects will be identified.

Active vaccination in patients with common variable immunodeficiency (CVID)

Active vaccination of CVID patients with standard vaccines has rarely been studied in depth although some patients have been shown to develop transient vaccine-specific immunity. We addressed the question whether these patients can be identified by functional classification of their B cell subsets in vitro. Twenty-one CVID patients receiving regular IgG substitution were immunized with anti-peptide and anti-polysaccharide vaccines. Humoral vaccination responses were compared to the numbers of circulating memory B cells, CD21(low) B cells and the capacity to produce antibodies in vitro. Our findings allow four conclusions: (1) positive vaccination responses are not contradictory to the diagnosis of CVID; they occurred against polypeptide vaccines in 23% and against polysaccharide antigens in 18% of all vaccinations. (2) Class-switched antibody responses occur preferentially in patients of CVID group II. (3) A normal percentage of IgM memory B cells is necessary but not sufficient for a vaccination response to polysaccharide antigens. (4) Active vaccination in addition to IgG replacement therapy should be performed in patients of CVID type II - especially in case of vaccines for which passive protection cannot be guaranteed.

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.

High serum levels of BAFF, APRIL, and TACI in common variable immunodeficiency

Common variable immunodeficiency (CVID) is characterized by low levels of immune globulins and lack of antibody. Mutations in transmembrane activator and calcium-modulating cyclophilin ligand (TACI), are found in 8-10%, associated with autoimmunity and splenomegaly. Some patients with mutations had increased serum levels of TACI. Because of this, and the prevalence of autoimmunity, splenomegaly, and lymphadenopathy, we quantitated levels of TACI ligands, a proliferation inducing ligand (APRIL) and B cell activating factor (BAFF) and TACI in serum of 77 patients. CVID subjects had markedly increased serum levels of BAFF (p<0.0001), APRIL (p<0.0001), and TACI (p=0.001) but there was no relationship between levels and autoimmunity, lymphadenopathy, splenomegaly, B cell numbers, or mutations in TACI. Peripheral blood mononuclear cells of CVID subjects had increased levels of BAFF mRNA. We conclude that increased constitutive production and/or underlying immuno-regulatory or inflammatory conditions lead to enhanced release of ligands; however, the biological result remains unclear.

Common Variable Immunodeficiency

BACKGROUND

Malabsorption syndrome often develops in patients with common variable immunodeficiency (CVID). Why structural damages appear in some CVID patients and not in others is not fully understood. Memory B cells (MBs) are responsible for the production of specific antibodies, and their defects have previously been related to autoimmune, granulomatous, and lymphoproliferative complications of CVID. The objective of this study was to ascertain whether a relationship exists between MB defects and the clinical outcome of respiratory and intestinal involvement in these patients.

METHODS

Forty-one CVID patients were grouped as follows, according to the quantification of peripheral MBs: the MB2 group (n = 7) included patients with normal MBs; the MB1 group (n = 16) included patients with low switched MBs; and the MB0 group (n = 18) included patients with absent/low MBs. The clinical outcome of respiratory and intestinal involvement of patients was then compared among the three groups.

RESULTS

In the MB0 group, chronic lung disease (ie, bronchiectasis and diminished FVC and/or FEV1) developed in 50% of patients vs 13% in the MB1 group and 0% in the MB2 group (p < 0.05). In the MB0 group, malabsorption syndrome or chronic noninfectious diarrhea developed in 50% of patients vs 19% in the MB1 group and 0% in the MB2 group (p < 0.05). No differences were found among the three groups for age at onset of symptoms, delay in diagnosis/treatment, months of follow-up/treatment, and prediagnostic serum IgG concentration.

CONCLUSIONS

Alterations in MB count appear to be associated with a severe clinical outcome of respiratory and intestinal involvement in CVID. The MB count could be a useful laboratory parameter for orienting the prognosis and management of CVID patients.

Deconstructing common variable immunodeficiency by genetic analysis

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency. Patients have recurrent bacterial infections and an increased risk of developing autoimmune diseases, lung damage, and selected cancers. Since 2003, four genes have been shown to be mutated in CVID patients: ICOS, TNFRSF13B (encoding TACI), TNFRSF13C (encoding BAFF-R) and CD19. Heterozygous mutations in TNFRSF13B are also associated with CVID, whereas the other three genes are purely recessive. Recent genetic linkage studies have also identified possible loci for dominant CVID genes on chromosomes 4q, 5p and 16q. These findings markedly improved the genetic diagnosis of CVID and point towards new strategies for future genetic studies. In addition, some CVID genes might be relevant to more common diseases such as asthma and stroke.

Immunodeficiency in childhood

Primary immunodeficiency disorders (PIDs) continue to illuminate mechanisms of human immunity and hypersensitivity. New discoveries in common variable immunodeficiency, the most enigmatic of PID syndromes, reveal molecular pathways of importance in human antibody production. FOXP3 mutations demonstrate the essential role that T-regulatory cells play in controlling autoantibody formation and disease. Interleukin-1 receptor-associated kinase 4 deficiency emphasizes the key role that innate immunity plays in the defense of bacterial disease occurring early in life. With respect to therapy, subcutaneous immunoglobulin treatment may indeed be a better treatment than intravenous immunoglobulin for many patients with antibody deficiency. Finally, PIDs remain in the vanguard for the treatment of inherited disorders by gene therapy. Gene therapy has cured patients with chronic granulomatous disease and severe combined immunodeficiency, but not without morbidity and mortality. Into the 21st century, PIDs continue to instruct us in human health and disease.

Common variable immunodeficiency: The power of co-stimulation

Common variable immunodeficiency (CVID) is the most frequent symptomatic primary immune deficiency in adults. CVID is characterized by the sequelae of an antibody deficiency syndrome: an impaired terminal B cell differentiation results in hypogammaglobulinemia and susceptibility to recurrent infections by encapsulated bacteria. The clinical course of CVID is complicated by a plethora of systemic immunopathology, including autoimmunity, lymphoproliferation, malignancy and sarcoid-like granulomas. Phenotypic and functional studies in CVID patients revealed multiple abnormalities within the innate and adaptive immune system. The recent description of monogenic defects in ICOS, TACI and CD19 focussed our interest to an impaired T cell-B cell collaboration within the germinal center and intrinsic B cell defects as possible explanations for the etiology of CVID.

Common variable immunodeficiency. Old questions are getting clearer

Common variable immunodeficiency (CVID) is a heterogeneous entity characterized by an impaired ability to produce antibodies. The failure is localized in partially mature B lymphocytes, though T lymphocyte abnormalities are occasionally present. This deficiency affects antibody synthesis and class switch from IgD and IgM, to IgG and IgA. CVID is related to selective IgA deficiency, and both abnormalities may coincide in one same family, and evolve from one to another in the same patient. The symptoms generally manifest in adults, but can occur at any age, even in infancy. Recurrent bacterial infections or pneumonias are frequent, and may be complicated by gastrointestinal problems, granulomas, autoimmune disorders or malignancies. A defect in memory B cells seems to condition the clinical severity. Recently, several mutations in genes encoding for molecules (CD19, TACI, ICOS) involved in B cell survival and isotype switch have been identified in patients with CVID. Nevertheless, genetic abnormalities have been found in less than 25 % of cases with CVID; the underlying mechanism thus remains unknown in the majority of CVID patients, and research in this field must continue.