title: Noninfectious complications in patients with pediatric-onset common variable immunodeficiency correlated with defects in somatic hypermutation but not in class-switch recombination.
abstract: BACKGROUND
  Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by impaired immunoglobulin production and usually presents with a normal quantity of peripheral B cells. Most attempts aiming to classify these patients have mainly been focused on T- or B-cell phenotypes and their ability to produce protective antibodies, but it is still a major challenge to find a suitable classification that includes the clinical and immunologic heterogeneity of these patients.
  
  
  OBJECTIVE
  In this study we evaluated the late stages of B-cell differentiation in a heterogeneous population of patients with pediatric-onset CVID to clinically correlate and assess their ability to perform somatic hypermutation (SHM), class-switch recombination (CSR), or both.
  
  
  METHODS
  We performed a previously reported assay, the restriction enzyme hotspot mutation assay (IgκREHMA), to evaluate in vivo SHM status. We amplified switch regions from genomic DNA to investigate the quality of the double-strand break repairs in the class-switch recombination process in vivo. We also tested the ability to generate immunoglobulin germline and circle transcripts and to upregulate the activation-induced cytidine deaminase gene through in vitro T-dependent and T-independent stimuli.
  
  
  RESULTS
  Our results showed that patients could be classified into 2 groups according to their degree of SHM alteration. This stratification showed a significant association between patients of group A, severe alteration, and the presence of noninfectious complications. Additionally, 60% of patients presented with increased microhomology use at switched regions. In vitro activation revealed that patients with CVID behaved heterogeneously in terms of responsiveness to T-dependent stimuli.
  
  
  CONCLUSIONS
  The correlation between noninfectious complications and SHM could be an important tool for physicians to further characterize patients with CVID. This categorization would help to improve elucidation of the complex mechanisms involved in B-cell differentiation pathways.
authors.affiliation: Servicio de Immunología y Reumatología, Hospital Nacional de Pediatría Prof. Dr Juan P. Garrahan, Buenos Aires, Argentina. Electronic address: mbalmejun@gmail.com.
authors.forename: María Belén
authors.initials: MB
authors.lastname: Almejún
authors.affiliation: Coordinación de Laboratorio, Hospital Nacional de Pediatría Prof. Dr Juan P. Garrahan, Buenos Aires, Argentina.
authors.forename: Bárbara Carolina
authors.initials: BC
authors.lastname: Campos
authors.affiliation: Unidad de Proteínas Recombinantes, Instituto Pasteur, Montevideo, Uruguay.
authors.forename: Virginia
authors.initials: V
authors.lastname: Patiño
authors.affiliation: Hospital de Niños Víctor J. Vilela, Rosario, Santa Fé, Argentina.
authors.forename: Miguel
authors.initials: M
authors.lastname: Galicchio
authors.affiliation: Servicio de Immunología y Reumatología, Hospital Nacional de Pediatría Prof. Dr Juan P. Garrahan, Buenos Aires, Argentina.
authors.forename: Marta
authors.initials: M
authors.lastname: Zelazko
authors.affiliation: Servicio de Immunología y Reumatología, Hospital Nacional de Pediatría Prof. Dr Juan P. Garrahan, Buenos Aires, Argentina.
authors.forename: Matías
authors.initials: M
authors.lastname: Oleastro
authors.affiliation: Unidad de Proteínas Recombinantes, Instituto Pasteur, Montevideo, Uruguay.
authors.forename: Pablo
authors.initials: P
authors.lastname: Oppezzo
authors.affiliation: Servicio de Immunología y Reumatología, Hospital Nacional de Pediatría Prof. Dr Juan P. Garrahan, Buenos Aires, Argentina.
authors.forename: Silvia
authors.initials: S
authors.lastname: Danielian
mesh_terms: D000293:Adolescent; D001402:B-Lymphocytes / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D017074:Common Variable Immunodeficiency / Q000235:genetics* / Q000276:immunology*; D005260:Female; D006801:Humans; D007134:Immunoglobulin Switch Region; D007223:Infant; D007963:Leukocytes, Mononuclear; D008297:Male; D011995:Recombination, Genetic; D027041:Somatic Hypermutation, Immunoglobulin
keywords: Common variable immunodeficiency; class-switch recombination; hypermutation; pediatric; somatic hypermutation; switch