Class switch recombination process in ataxia telangiectasia patients with elevated serum levels of IgM.

Ataxia telangiectasia (AT) is a rare primary immunodeficiency disorder with various clinical manifestations. Increased serum levels of IgM and recurrent infections, mainly sinopulmonary infections, can be the presenting feature in a number of AT patients and may be initially misdiagnosed as hyper-IgM (HIgM) syndrome. This study was designed to investigate class switch recombination (CSR) as a critical mechanism in B lymphocytes' maturation to produce different isotypes of antibody in response to antigen stimulation in AT cases with HIgM presentation. Quantitative IgE production after stimulation by IL-4 and CD40L was considered as an indicator for CSR function. We also compared their results with sex and age matched AT patients without HIgM presentation. We report four AT patients with recurrent infections during infancy and high serum levels of IgM. Laboratory evaluations revealed defective CSR while none of the three AT patients without HIgM presentation had a defect in the CSR process. The characterized defect in AT is a mutation in the ataxia telangiectasia mutated (ATM) gene. This gene may result in CSR defects due to impaired DNA break repair. A special association between AT and HIgM may indicate a new subgroup of AT patients according to their clinical phenotype and CSR condition.

Evaluation of antibody response to polysaccharide vaccine and switched memory B cells in pediatric patients with inflammatory bowel disease.

BACKGROUND/AIMS: Inflammatory bowel disease (IBD) is a chronic disease of the gastrointestinal tract, whose etiologies are still unknown. This study was performed to evaluate the humoral immune response in terms of B cell functions in selected IBD patients. METHODS: Eighteen pediatric patients with IBD, including 12 cases of ulcerative colitis (UC) and six with Crohn disease (CD), were enrolled in this study. The pneumococcal vaccine was injected in all patients, and the IgG antibody level to the polysaccharide antigen was measured before and 4 weeks after injection. The B cell switch-recombination process was evaluated. RESULTS: Five patients with IBD (three CD and two UC) had defects in B cell switching, which was significantly higher than in controls (p=0.05). Ten patients had a specific antibody deficiency and exhibited a higher frequency of bacterial infection than the healthy group. The mean increased level of IgG after vaccination was lower in IBD patients (82.9±32.5 µg/mL vs 219.8±59.0 µg/mL; p=0.001). Among the patients who had an insufficient response, no significant difference in the number of switched memory B-cell was observed. CONCLUSIONS: A defect in B lymphocyte switching was observed in pediatric IBD patients, and especially in those patients with CD. Owing to an increased risk of bacterial infections in those patients with antibody production defects, pneumococcal vaccination could be recommended. However, not all patients can benefit from the vaccination, and several may require other prophylactic methods.

Evaluation of class switch recombination in B lymphocytes of patients with common variable immunodeficiency.

Common variable immunodeficiency (CVID) is a heterogeneous group of disorders characterized by hypogammaglobulinemia and recurrent bacterial infections. Impaired antibody production in these patients is due to defect in B-cell differentiation into specific plasma cells. Class switch recombination (CSR), which plays a critical role in the production of different immunoglobulin isotypes, may be defective in a group of CVID patients. The aim of this study was to investigate the CSR process in B cells of CVID patients, by evaluating the expression of IgE mRNA and production of its protein in an IgE inductive medium. Peripheral blood mononuclear cells (PBMCs) from 29 CVID patients and 21 healthy controls were isolated and cultured in the presence of rhIL-4 and CD40L. IgE mRNA and IgE protein were measured by RT-PCR and ELISA techniques, respectively. Normal production of IgE mRNA was recorded in 23 out of 29 patients (79.31%) as well as all controls; while the remaining 6 patients (20.69%) were unable to express IgE mRNA indicating a defect in CSR. PBMCs of 16 out of 29 patients (55.2%) could not produce normal amounts of IgE compared with controls, after being stimulated by IL-4 and CD40L. Post B cell stimulation IgE production was impaired in about half of studied CVID patients. Defects in processes occur following the CSR process such as IgE mRNA transcription, protein production, and secretion can be the causative mechanism of CVID in patients with normal mRNA expression of the immunoglobulin but impaired protein production. Determination of these defects can help to clarify the various underlying mechanisms responsible for the development of CVID.

Expression of activation-induced cytidine deaminase gene in B lymphocytes of patients with common variable immunodeficiency.

OBJECTIVE: Common variable immunodeficiency (CVID) is a heterogeneous disorder characterized by reduced serum level of IgG, IgA or IgM and recurrent bacterial infections. Class switch recombination (CSR) as a critical process in immunoglobulin production is defective in a group of CVID patients. Activation-induced cytidine deaminase (AID) protein is an important molecule involving CSR process. The aim of this study was to investigate the AID gene mRNA production in a group of CVID patients indicating possible role of this molecule in this disorder. METHODS: Peripheral blood mononuclear cells (PBMC) of 29 CVID patients and 21 healthy controls were isolated and stimulated by CD40L and IL-4 to induce AID gene expression. After 5 days AID gene mRNA production was investigated by real time polymerase chain reaction. FINDINGS: AID gene was expressed in all of the studied patients. However the mean density of extracted AID mRNA showed higher level in CVID patients (230.95±103.04 ng/ml) rather than controls (210.00±44.72 ng/ml; P=0.5). CVID cases with lower level of AID had decreased total level of IgE (P=0.04) and stimulated IgE production (P=0.02); while cases with increased level of AID presented higher level of IgA (P=0.04) and numbers of B cells (P=0.02) and autoimmune disease (P=0.02). CONCLUSION: Different levels of AID gene expression may have important roles in dysregulation of immune system and final clinical presentation in CVID patients. Therefore investigating the expression of AID gene can help in classifying CVID patients.