Impaired Antibody Production Research Articles

Prevalence and clinical challenges among adults with primary immunodeficiency and recombination-activating gene deficiency

Prevalence and clinical challenges among adults with primary immunodeficiency and recombination-activating gene deficiency

Chronic helminth infection burden differentially affects haematopoietic cell development while ageing selectively impairs adaptive responses to infection

Throughout the lifespan of an individual, the immune system undergoes complex changes while facing novel and chronic infections. Helminths, which infect over one billion people and impose heavy livestock productivity losses, typically cause chronic infections by avoiding and suppressing host immunity. Yet, how age affects immune responses to lifelong parasitic infection is poorly understood. To disentangle the processes involved, we employed supervised statistical learning techniques to identify which factors among haematopoietic stem and progenitor cells (HSPC), and both innate and adaptive responses regulate parasite burdens and how they are affected by host age. Older mice harboured greater numbers of the parasites’ offspring than younger mice. Protective immune responses that did not vary with age were dominated by HSPC, while ageing specifically eroded adaptive immunity, with reduced numbers of naïve T cells, poor T cell responsiveness to parasites, and impaired antibody production. We identified immune factors consistent with previously-reported immune responses to helminths, and also revealed novel interactions between helminths and HSPC maturation. Our approach thus allowed disentangling the concurrent effects of ageing and infection across the full maturation cycle of the immune response and highlights the potential of such approaches to improve understanding of the immune system within the whole organism.

Mannose-Binding Lectin Protein Deficiency Among Patients with Primary Immunodeficiency Disease Receiving IVIG Therapy.

Primary immunodeficiencies (PIDs) are inherited disorders in which one or several components of the immune system are defective. Immunoglobulin replacement therapy is the mainstay of treatment for patients with impaired antibody production. However, recurrent infections would continue to occur in some patients due to the other high frequent concomitant defects, such as mannose-binding lectin (MBL) deficiency. A total of 51 PID patients participated in this cross-sectional study. A detailed questionnaire was completed by interviewing patients in order to record demographic, clinical and laboratory data. The levels of MBL were determined in the serums of patients by a sandwich enzyme-linked immunosorbent assay (ELISA) technique. MBL deficiency was found in 29.4% of cases; 11.8% patients had mild, 3.9% patients had moderate and 13.7% patients had severe MBL deficiency. In patients with MBL deficiency, the rate of meningitis, sepsis, pneumonia, and otitis media was higher than patients with normal MBL levels. Immunoglobulin replacement therapy reduced the rate of infectious complications in PID patients; however, these reductions were more apparent in patients with normal MBL levels than patients with MBL deficiency. Antibody deficient patients with a concomitant immune defect in MBL production have higher rates of recurrent infections despite receiving Immunoglobulin replacement therapy.

Evaluation of Clinical and Immunological Characteristics of Children with Common Variable Immunodeficiency.

Background Common variable immunodeficiency (CVID) is a primary immunodeficiency disorder (PID) that typically presents with hypogammaglobulinemia and impaired antibody production. Objectives This study aimed to promote the awareness of CVID, whose clinical spectrum is quite broad. Methods The demographic, clinical, and laboratory characteristics of 12 children (seven males and five females) with CVID were analyzed retrospectively. The patients were diagnosed using the diagnostic criteria of the European Society for Primary Immunodeficiencies. Results The median disease onset age was 7.2 ± 4.1 years, and the mean diagnosis age was 11.6 ± 3.7 years. The diagnosis delay was 4.3 ± 2.6 years, and the parental consanguinity rate was 75%. Most patients presented with recurrent infections, including upper respiratory tract infections (n = 8), lower respiratory tract infections (n = 9), and gastroenteritis (n = 5). In addition, growth retardation (n = 9) and bronchiectasis (n = 5) were common comorbidities. Two patients presented with autoimmune thrombocytopenia and anemia, and one patient exhibited lung empyema. All the patients had immunoglobulin G deficiencies. Conclusion CVID is a heterogeneous disease, so the diagnosis is frequently delayed. In the CVID patients with pulmonary complications, relationships were seen with the diagnosis delay, symptom onset age, and lung infection prevalence. Overall, the early diagnosis and treatment of PIDs can preclude life-threatening complications.

Renal Evaluation in Common Variable Immunodeficiency.

Introduction Common variable immunodeficiency (CVID) comprises a heterogeneous group of disorders characterized by impaired antibody production. Kidney involvement in CVID is described in isolated and sporadic case reports. The objective of this study was to study the renal function pattern in CVID patients through glomerular and tubular function tests. Methods Study of 12 patients with CVID diagnosis and 12 healthy control individuals. Glomerular filtration rate (GFR), fractional excretion of sodium (FENa+) and potassium (FEK+), urinary concentration, and acidification capacity were measured. In addition, microalbuminuria and urinary monocyte chemoattractant protein-1 (MCP-1) were evaluated as markers of selectivity of the glomerular barrier and inflammation, respectively. Results In relation to glomerular markers, all CVID patients had normal GFR (>90 mL/min/1.73 m2), and microalbuminuria and urinary MCP-1 levels were also similar to those of controls. Interestingly, CVID patients had reduced urinary concentration capacity, as demonstrated by lower U/POsm ratio, when compared to controls. Also, while all control subjects achieved a urinary pH less than 5.3, no CVID patients showed a decrease in urinary pH to such levels in response to acid loading with CaCl2, characterizing impaired urinary acidification capacity. Conclusion Patients showed a trend towards an elevated prevalence of tubular dysfunction, mainly related to urinary acidification and concentration capacities.

Altered follicular helper T cell impaired antibody production in a murine model of myelodysplastic syndromes.

Myelodysplastic syndromes (MDS) are a group of clonal hematopoietic diseases which have a high risk of progressing to acute myeloid leukemia. MDS patients have immunologic deficiency, including T and B cells dysfunction. Follicular T helper cells (Tfh, CD4+CXCR5+) are an important subset of helper T cells which help to the formation of germinal centers and B cells differentiation. In this study, we investigated the proportion and function of Tfh using NUP98-HOXD13 transgenic (NHD13) mice model with MDS phenotype. The proportion of Tfh from bone marrow and spleen of NHD13 mice decreased compared with wild type (WT) mice tested by flow cytometry. In NHD13 mice spleens, there were decreased CXCR5+ cells and increased PD-1+ cells using immunohistochemistry. The active markers (ICOS, CD40L and OX40) expressed on Tfh of NHD13 mice were decreased. In contrast, PD-1 expression on Tfh of NHD13 mice was higher than that of WT mice. After coculture with Tfh from NHD13 mice, IgG and IgM production of B cells were decreased. In conclusion, the proportion and function of Tfh in the MDS mice model were altered. The dysfunction and reduction of Tfh may inhibit B cells differentiation and antibody production. Abnormal Tfh might contribute to the immune tolerance promoting the progression of MDS.

Somatic Hypermutation Defects in Common Variable Immune Deficiency.

Common variable immunodeficiency (CVID) is a heterogeneous disorder characterized by impaired antibody production and recurrent infections. In the last 20years, several groups have reported that B cells from CVID patients have an impaired somatic hypermutation (SHM). The reported frequency of this defect among CVID patient cohorts is highly variable and so is the methodology used to evaluate this process. Interestingly, the low level of SHM on B cells from CVID patients has been correlated with the presence of infectious and non-infectious complications. In this review, an overview of the studies regarding SHM in CVID patients is presented. We highlight the importance of SHM studies in CVID patients as a clinical tool due to the reported association with clinical complications by several groups. We also considered SHM measurement useful to guide future investigations in order to identify genetic defects involved in the development of the disease.

Total and High Molecular Weight Adiponectin Expression Is Decreased in Patients with Common Variable Immunodeficiency: Correlation with Ig Replacement Therapy.

Adiponectin (Acrp30) is an adipokine widely studied for its beneficial metabolic properties. It circulates as low molecular weight (LMW), medium molecular weight (MMW), and high molecular weight (HMW) oligomers. The latter exerts the most potent biological effects. Acrp30 attracted renewed interest with the finding that it was associated with the development and progression of immune disorders. The mechanisms underlying this association and the role of Acrp30 in the pathophysiology of immune-mediated conditions remain unknown. Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by chronic activation of the immune system, impaired antibody production, and imbalanced cytokine production. In the attempt to shed light on the expression of Acrp30 in CVID, we: (a) investigated total Acrp30 and its oligomerization state in CVID patients undergoing maintenance Ig replacement therapy; (b) assessed the effects of Ig replacement therapy on Acrp30 expression in treatment-naïve CVID patients, namely, patients not treated before diagnosis, before and after the first Ig administration; and (c) evaluated the correlation between Acrp30 levels and clinical phenotypes of the disease. As controls, we analyzed healthy subjects and patients affected by a non-immunodeficiency chronic inflammatory demyelinating polyneuropathy (CIDP), before and after Ig infusion. We found that total Acrp30 and HMW oligomers were decreased in CVID but not in CIDP patients versus controls. Moreover, Acrp30 levels were correlated with IgA levels and were associated with two CVID phenotypes, namely, autoimmune cytopenia and enteropathy. Receiver operating characteristic curve analysis indicated that Acrp30 modulation is specific for CVID patients. Acrp30 and HMW levels quickly and dramatically increased after Ig infusion only in eight treatment-naïve CVID patients but not in five CIDP patients. This finding indicates that Ig administration per se is not able to induce an increase of Acrp30, but the specific cellular and/or molecular background proper of CVID seems to be essential. In conclusion, our data indicate that Acrp30 is specifically related to CVID activity. Further studies are required to understand the biological role of Acrp30 and its possible use as disease biomarker in CVID.

Delay in diagnosis affects the clinical outcome in a cohort of cvid patients with marked reduction of iga serum levels

Common variable immunodeficiency disorders (CVID) represent a collection of diseases leading to an absent or strongly impaired antibody production. CVID presents a wide range of immunological abnormalities and clinical manifestations, including infections, inflammatory and autoimmune diseases, and malignancies. The aim of this observational study was to analyze the epidemiological and clinical features of a cohort of 75 Italian CVID patients, and evaluate the correlation with comorbidity and mortality. Clinical data were retrospectively collected: the cohort was followed-up for a maximum of 30years (mean time of 10.24years, median of 9years). An higher age at the diagnosis of CVID and an higher age at onset of symptoms were significantly associated with a reduction of patients survival if stratified per median of IgA (less than or >8.00mg/dl). Thus IgA levels at diagnosis are correlated with patients survival contributing to identify a subset with a worse prognostic outcome.

Is immunotherapy here to stay in multiple myeloma?

Immune escape and impaired immune surveillance have been identified as emerging hallmarks of cancer.1 Multiple myeloma represents a genuine example of disrupted immune surveillance characterized by: impaired antibody production, deregulation of the T and natural killer cell compartment, disruption of antigen presentation machinery, upregulation of inhibitory surface ligands, and recruitment of immunosuppressive cells. Although the potential value of immunotherapeutic interventions had a clear antecedent in the graft-versus-myeloma effect induced by allogeneic stem cell transplant and donor lymphocyte infusions, it is only recently that this field has faced a real revolution. In this review we discuss the current results obtained with immune approaches in patients with multiple myeloma that have placed this disease under the scope of immuno-oncology, bringing new therapeutic opportunities for the treatment of multiple myeloma patients.

Abstract 13062: Pathogenic IgG Antibodies in Hyperlipidemic Mice Promote Atherosclerosis

Background: B2 cells promote atherosclerosis, but the exact mechanisms by which they promote atherosclerosis are not known. Antibodies can be pathogenic in a number of chronic inflammatory diseases. Here, we examined the role of antibodies in the development of atherosclerosis in hyperlipidemic mice. Methods and Results: As an interaction between B cells and CD4 T cells is important for plasma cell development and antibody production, we generated mixed chimeric LDLR -/- mice with B cells selectively deficient in MHC II or CD40 molecules. B cells deficient in either molecule decreased atherosclerosis by ~30-40%. This was associated with reduced spleen germinal centre B cells and plasma cells, markedly reduced plasma total immunoglobulins, reduced spleen CD4 T cell activation and decreased IFN-γ+ CD4 T cells. To confirm that the observed effects on atherosclerosis were largely due to impaired plasma cell generation and antibody production, we also deleted B cell-specific Blimp-1, a transcription factor critically important for B cell differentiation into antibody-producing plasma cells. Chimeric LDLR -/- mice transplanted with CD23 CRE -Blimp-1 fl/fl bone marrow were completely devoid of spleen plasma cells and plasma total immunoglobulins but CD4+ T cell activation was unaffected; atherosclerosis in these mice was reduced by nearly 50%. To exclude the possibility that the reduction in atherosclerosis was due to deletion of plasma cells, we then purified IgG from hyperlipidemic mice with atherosclerosis and transferred the IgG into immunoglobulin/plasma cell-deficient CD23 CRE -Blimp-1 fl/fl bone marrow transplanted LDLR -/- mice. Atherosclerotic lesions doubled in size in mice that received IgG from atherosclerotic mice, compared to transfer of IgG purified from non-atherosclerotic mice. Conclusions: Our study indicates that IgG antibodies generated in hyperlipidemic mice during atherosclerosis development accelerates growth of atherosclerotic lesions. Targeting pathogenic IgG antibodies in atherosclerosis has a potential to reduce lesion progression and the incidence of heart attacks and strokes.

Targeting the phosphatidylinositol 3-kinase signaling pathway to inhibit pathogenic B cells in systemic lupus erythematosus (SLE)

Abstract Systemic Lupus Erythematosus (SLE) is an autoimmune disease with high levels of autoreactive B cells and circulating anti-nuclear autoantibodies. Circulating antibody-antigen immune complexes deposit in tissues, including the kidney, causing chronic inflammation and irreparable tissue damage. The hematopoietic system expresses a unique isoform of the phosphatidylinositol 3 kinase (PI3K) catalytic subunit, termed delta (PI3Kδ). It is critical for B cell survival and function, and its inhibition results in impaired antibody production. We hypothesized that targeting PI3Kδ will decrease levels of circulating auto-antibodies in a mouse model of SLE and reduce disease pathology. This study shows that a clinically utilized small molecule inhibitor of PI3Kδ (GS-9820) significantly inhibits naïve B cell differentiation into antibody secreting plasma cells as well as B cell proliferation in vitro. Furthermore, in the (NZBxNZW)F1 mouse model of SLE, treatment with the PI3Kδ inhibitor reduced autoantibody levels to background and increased overall survival. Within 2 weeks of treatment animals showed a marked reduction of germinal center B cells and T follicular helper cells (Tfh). The decrease in autoantibody levels ultimately prevented kidney damage by reducing immune complex deposition and complement fixation. Current treatments for lupus predominantly utilize systemic immunosuppressive drugs which have severe side effects. Since PI3Kδ plays a predominant role in B cells, our data suggests a clinical PI3Kδ inhibitor can be a therapeutic for lupus, potentially reducing autoantibody levels and associated pathologies. This therapy can result in better disease management and quality of life for lupus patients.

Mis-acylation of tRNAs suppresses protective immune responses which control cutaneous inflammation by infection

Abstract The mouse sticky mutation which is a missense mutation in editing domain of the alanyl-tRNA synthetase gene impairs the proofreading activity during amino-acylation of tRNAs. An editing-defective tRNA synthetase induces the accumulation of mis-folded proteins in the neuron which is associated with neuro-degenerative disorder. Although the sticky mice were characterized by the rough, unkempt, sticky appearance, it is not clear whether the sticky mutation is associated with inflammatory disease. The protective role of T and B cells during cutaneous infection by a variety of pathogens has been known well. We therefore investigated how sticky mutation affects immune responses and linked to sticky phenotype. First of all, we examined immune cell numbers in sticky mice. LN cell number in sticky mice was significantly reduced compared to Sti/+ and WT mice, while LN profiles of sticky mice were not big different from control groups. Reduced cellularity by sticky mutant results from impaired proliferation, not by IL-7 signaling which is critical in T cell development and homeostasis. Interestingly, we found that mutation in tRNA processing reduced IFNγ and IL-17 production from stimulated T cells. And it also reduced Immunoglobulin production in B cells, particularly IgG1 and IgE which has an important role in resistance to bacterial and parasite infection. These findings indicate that disruption of translational fidelity induces deterioration of immune functions such as impaired cytokine and antibody production, resulting in reduction of the resistance to various infections. Furthermore, it provides a novel mechanism which the alteration of tRNA pool in inflammatory diseases affects the cellular and humoral immune responses.

The transcription factor BATF modulates cytokine-mediated responses in T cells

The transcription factor BATF (basic leucine zipper transcription factor, ATF-like), belongs to the AP-1 family of transcription factors and has been shown to be predominantly expressed in cells of haematopoietic origin, especially in B and T cells. In studies using Batf-deficient mice, a profound defect in the differentiation of T helper cells type 17 (Th17) and follicular T helper cells (Tfh) was described, as well as an impairment of antibody production with switched isotypes. More recently BATF has been described to influence also Th2 and Th9 responses in models of murine experimental asthma. In CD8+ T cells BATF has been found associated with anti-viral responses. This review summarizes the role of BATF in CD4+ T cell subsets and in CD8+ T cells, with particular focus on this transcription factor in the setting of allergic asthma.

Neonatal Tetanus Immunity in Nigeria: The Effect of HIV Infection on Serum Levels and Transplacental Transfer of Antibodies.

Background. Tetanus toxoid immunisation of pregnant mother has remained the most effective strategy in eliminating neonatal tetanus. Impaired production and/or transplacental transfer of antibodies may affect the effectiveness of this strategy. We studied the effect of maternal HIV infection on serum levels and transplacental transfer of anti-tetanus antibodies. Methods. A total of 162 mother-baby paired serum samples were taken and analysed for anti-tetanus antibody levels using ELISA. Maternal HIV status was also determined by double ELISA technique. Maternal TT vaccination status was also documented. Results. Thirty-eight (23.5%) mothers and 41 (25.3%) babies were seronegative, out of whom 8 mothers were HIV positive and 9 babies were HIV exposed. HIV infected mothers and HIV exposed infants were, respectively, 16.27 times (OR = 16.27, 95% CI = 3.28 to 80.61) and 33.75 times (OR = 33.75, 95% CI = 4.12 to 276.40) more likely to be seronegative for anti-tetanus antibody. Similarly, HIV positive mother-newborn pairs were 7.46 times more likely to have a poor transplacental transfer of tetanus antibodies (OR = 7.46, 95% CI = 1.96 to 28.41). Conclusions. Maternal HIV infection is associated with impaired maternofoetal transfer of anti-tetanus antibodies and seronegativity among mothers and their newborns. Hence, this may hinder efforts to eliminate neonatal tetanus.

Nck adaptor proteins modulate differentiation and effector function of T cells.

Understanding the molecular mechanisms regulating T cell reactivity is required for successful reprogramming of immune responses in medical conditions, characterized by dysfunctions of the immune system. Nck proteins are cytoplasmic adaptors mediating diverse cellular functions, including TCR signaling. By enhancing TCR signal strength, Nck proteins influence thymic selection and regulate the size and sensitivity of the peripheral T cell repertoire. Here, we investigated the contribution of Nck proteins to CD4(+) T cell differentiation and effector function using Nck.T(-/-) mice. Impaired GC formation and reduced Tfh were observed in Nck.T(-/-) mice after immunization with T cell-dependent antigens. Th2/Tfh-related cytokines, such as IL-4, IL-10, and IL-21, were decreased in Nck.T(-/-) mice T cells. Moreover, an increased susceptibility to cell death of Tfh cells in Nck.T(-/-) mice was associated with decreased levels of Akt phosphorylation. As a result of this dysregulation in Tfh cells of Nck.T(-/-) mice, we found impaired production and affinity maturation of antibodies against T cell-dependent antigens. Thus, Nck proteins not only participate in thymic selection and generation of the peripheral T cell repertoire but also are involved in the differentiation and effector functions of CD4(+) T cells.

Surface Plasmon Resonance Analysis Shows an IgG-Isotype-Specific Defect in ABO Blood Group Antibody Formation in Patients with Common Variable Immunodeficiency.

Common variable immunodeficiency (CVID) is the most common clinically severe primary immunodeficiency and comprises a heterogeneous group of patients with recurrent severe bacterial infections due to the failure to produce IgG antibodies after exposure to infectious agents and immunization. Diagnostic recommendations for antibody failure include assessment of isoagglutinins. We have readdressed this four decades old but still accepted recommendation with up to date methodology. Anti-A/B IgM- and IgG-antibodies were measured by Diamed-ID Micro Typing, surface plasmon resonance (SPR) using the Biacore(®) device and flow cytometry. When Diamed-ID Micro Typing was used, CVID patients (n = 34) showed IgG- and IgM-isoagglutinins that were comparable to healthy volunteers (n = 28), while all XLA patients (n = 8) had none. Anti-A/B IgM-antibodies were present in more than 2/3 of the CVID patients and showed binding kinetics comparable to anti-A/B IgM-antibodies from healthy individuals. A correlation could be found in CVID patients between levels of anti-A/B IgM-antibodies and levels of serum IgM and PnP-IgM-antibodies. In contrast in CVID patients as a group ABO antibodies were significantly decreased when assessed by SPR, which correlated with levels of switched memory, non-switched memory and naïve B cells, but all CVID patients had low/undetectable anti-A/B IgG-antibodies. These results indicate that conventional isoagglutinin assessment and assessment of anti-A/B IgM antibodies are not suited for the diagnosis of impaired antibody production in CVID. Examination of anti-A/B IgG antibodies by SPR provides a useful method for the diagnosis of IgG antibody failure in all CVID patients studied, thus indicating an important additional rationale to start immunoglobulin replacement therapy early in these patients, before post-infectious sequelae develop.

ICOSL-mediated signaling is essential for the survival and functional maturation of germinal center B cells through the classical NF-κB pathway (IRM10P.611)

Abstract The molecular mechanisms by which helper T-cells support B-cell activation, survival and functional differentiation in the germinal center (GC) are not well-defined. To date, signaling through CD40 by CD40L is the only established receptor-ligand signaling pathway initiated by helper T-cells. Here we show that helper T-cells provide helper signal to B-cells through the inducible T-cell co-stimulator (ICOS)-ICOS ligand (ICOSL) interaction. We found that reverse ICOSL signaling on GC B-cells is essential and sufficient to promote GC B-cell survival and functional maturation; whereas CD40-mediated signaling plays a minor role during GC reaction, although critical in initiating the GC response. In vivo ICOSL engagement by ICOS-Ig fusion protein can rescue impaired GC formation and antibody production in ICOS-deficient mice. Various lines of ICOSL mutant mice, including pan-B cell-specific ICOSL-deficient mice, GC B cell-specific ICOSL-deficient mice, and ICOSL intra-cellular domain mutant mice, all show defective humoral response and impaired GC reaction. ICOSL reverse signaling in GC B cells is dependent on activation of the classical NF-kB signal pathway, resulting in increased BCL2, c-MYC and FOXO1 expression that supports GC B cell survival and differentiation. Thus, CD40-CD40L interaction mainly supports the initiation of GC response, whereas ICOS-ICOSL collaboration provides bi-directional signals that support the maintenance and functional maturation of GC B cells.

Infección por Mycobacterium bovis en inmunodeficiencia común variable

Common variable immunodeficiency (CVID) is an heterogeneous group of disorders characterized by impaired antibody production. It shows a wide spectrum of manifestations including severe and recurrent respiratory infections (Streptococcus pneumoniae, Haemophilus) and gastrointestinal (Campylobacter jejuni, rotavirus and Giardia lamblia). Viral infections caused by herpes zoster, cytomegalovirus (CMV) and hepatitis C are rare. The opportunistic agents such as CMV, Pneumocystis jirovecii, cryptococcus and atypical mycobacteria have been reported as isolated cases. This paper reports the case of a 38-year-old female patient, who began six years before with weight loss of 7 kg in six months, fatigue, weakness, sweating, fever and abdominal pain. Furthermore, patient had intestinal obstruction and abdominal CT showed mesenteric lymph growth. The mesenteric lymph node biopsy revealed positives Mycobacterium PCR, Ziehl-Neelsen staining and culture for M. bovis. In the laparotomy postoperative period was complicated with nosocomial pneumonia, requiring mechanical ventilation and tracheostomy. Two years later, she developed right renal abscess that required surgical drainage, once again with a positive culture for Mycobacterium bovis. She was referred to highly specialized hospital and we documented panhypogammaglobulinemia and lymphopenia. Secondary causes of hypogammaglobulinemia were ruled out and common variable immunodeficiency (CVID) was confirmed, we started IVIG replacement. Four years later she developed mixed cellularity Hodgkin's lymphoma. Until today she continues with IVIG and chemotherapy. This report of a patient with CVID and Mycobacterium bovis infection, a unusual association, shows the cellular immunity susceptibility in this immunodeficiency, additional to the humoral defect.

Detection of impaired IgG antibody formation facilitates the decision on early immunoglobulin replacement in hypogammaglobulinemic patients.

Hypogammaglobulinemia (serum IgG lower than 2 SD below the age-matched mean) and clinical symptoms such as increased susceptibility to infection, autoimmune manifestations, granulomatous disease, and unexplained polyclonal lymphoproliferation are considered to be diagnostic hallmarks in patients with common variable immunodeficiency (CVID), the most frequent clinically severe primary immunodeficiency syndrome. In the present study, we investigated patients with hypogammaglobulinemia and no clinical or immunological signs of defective cell-mediated immunity and differentiated two groups on the basis of their IgG antibody formation capacity against a variety of different antigens (bacterial toxins, polysaccharide antigens, viral antigens). Patients with hypogammaglobulinemia and intact antibody production (HIAP) displayed no or only mild susceptibility to infections, while CVID patients showed marked susceptibility to bacterial infections that normalized following initiation of IVIG or subcutaneous immunoglobulin replacement therapy. There was a substantial overlap in IgG serum levels between the asymptomatic HIAP group and the CVID patients examined before immunoglobulin treatment. HIAP patients showed normal levels of switched B-memory cells (CD19+CD27+IgD−), while both decreased and normal levels of switched B-memory cells could be found in CVID patients. IgG antibody response to a primary antigen, tick-borne encephalitis virus (TBEV), was defective in CVID patients, thus confirming their substantial defect in IgG antibody production. Defective IgG antibody production against multiple antigens could also be demonstrated in an adult patient with recurrent infections but normal IgG levels. To facilitate early treatment before recurrent infections may lead to organ damage, the antibody formation capacity should be examined in hypogammaglobulinemic patients and the decision to treat should be based on the finding of impaired IgG antibody production.