title: Human CD19 and CD40L deficiencies impair antibody selection and differentially affect somatic hypermutation.
abstract: BACKGROUND
  Individuals with genetic defects in CD40 ligand (CD40L) or B-cell antigen receptor coreceptor molecules CD19 and CD81 suffer from an antibody deficiency. Still, these patients carry low levels of memory B cells and serum antibodies.
  
  
  OBJECTIVE
  We sought to assess why the remaining memory B cells and antibodies in the blood of these patients do not provide functional immunity.
  
  
  METHODS
  We included CD19-deficient patients (n = 8), CD40L-deficient patients (n = 8), and healthy controls (n = 50) to perform detailed flow cytometry on blood B cells, molecular analysis of IgA and IgG transcripts, as well as functional analysis of B-cell activation.
  
  
  RESULTS
  CD19-deficient and CD40L-deficient patients carried reduced numbers of all memory B-cell subsets except CD27(-)IgA(+) B cells. Their immunoglobulin heavy chain class-switched transcripts contained less somatic mutations and reduced usage of IgM-distal IgG2 and IgA2 subclasses. The selection strength of mutations for antigen binding was significantly lower than in controls, whereas selection to maintain superantigen binding was normal. Furthermore, the patients showed impaired selection against inherently autoreactive properties of their immunoglobulins. Somatic hypermutation analysis revealed decreased activation-induced cytidine deaminase and uracil-DNA glycosylase 2 activity in CD40L deficiency and increased uracil-DNA glycosylase 2 but decreased mismatch repair in CD19 deficiency. B-cell activation studies revealed that this was at least in part due to transcriptional regulation of DNA repair genes.
  
  
  CONCLUSIONS
  This study on CD19 and CD40L deficiencies illustrates that both the B-cell antigen receptor and CD40 signaling pathways are required for the selection of immunoglobulin reactivity. Still, they differentially mediate DNA repair pathways during somatic hypermutation, thereby together shaping the human in vivo antigen-experienced B-cell repertoire.
authors.affiliation: Department of Immunology, Erasmus MC, Rotterdam, The Netherlands. Electronic address: m.vanzelm@erasmusmc.nl.
authors.forename: Menno C
authors.initials: MC
authors.lastname: van Zelm
authors.affiliation: Department of Immunology, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: Sophinus J W
authors.initials: SJ
authors.lastname: Bartol
authors.affiliation: Department of Immunology, Erasmus MC, Rotterdam, The Netherlands; Department of Pediatrics, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: Gertjan J
authors.initials: GJ
authors.lastname: Driessen
authors.affiliation: Immunobiology Clinic, Hôpital Erasme, and Laboratory of Vaccinology and Mucosal Immunity, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: Françoise
authors.initials: F
authors.lastname: Mascart
authors.affiliation: Meram Medical Faculty, Department of Pediatric Immunology and Allergy, Necmettin Erbakan University, Konya, Turkey.
authors.forename: Ismail
authors.initials: I
authors.lastname: Reisli
authors.affiliation: Group of Primary Immunodeficiencies, University of Antioquia, Medellín, Colombia.
authors.forename: Jose L
authors.initials: JL
authors.lastname: Franco
authors.affiliation: Department of Immunology, Children's Memorial Health Institute, Warsaw, Poland.
authors.forename: Beata
authors.initials: B
authors.lastname: Wolska-Kusnierz
authors.affiliation: Department of Pediatrics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Kanegane
authors.affiliation: Bioceros B.V., Utrecht, The Netherlands.
authors.forename: Louis
authors.initials: L
authors.lastname: Boon
authors.affiliation: Department of Immunology, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: Jacques J M
authors.initials: JJ
authors.lastname: van Dongen
authors.affiliation: Department of Immunology, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: Mirjam
authors.initials: M
authors.lastname: van der Burg
mesh_terms: D000328:Adult; D018941:Antigens, CD19 / Q000235:genetics / Q000276:immunology*; D016175:B-Lymphocyte Subsets / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D023201:CD40 Ligand / Q000172:deficiency / Q000235:genetics / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D003564:Cytidine Deaminase / Q000235:genetics / Q000276:immunology; D004260:DNA Repair / Q000276:immunology; D005260:Female; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D006801:Humans; D007070:Immunoglobulin A / Q000235:genetics / Q000276:immunology*; D017578:Immunoglobulin Class Switching; D007074:Immunoglobulin G / Q000235:genetics / Q000276:immunology*; D007153:Immunologic Deficiency Syndromes / Q000235:genetics / Q000276:immunology* / Q000473:pathology; D007156:Immunologic Memory; D016130:Immunophenotyping; D007223:Infant; D008213:Lymphocyte Activation; D018655:Lymphocyte Count; D008297:Male; D008875:Middle Aged; D009154:Mutation; D015398:Signal Transduction; D051981:Uracil-DNA Glycosidase / Q000235:genetics / Q000276:immunology
chemical_list: D018941:Antigens, CD19; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D023201:CD40 Ligand; D051981:Uracil-DNA Glycosidase; D003564:Cytidine Deaminase
keywords: CD19; CD40L; autoreactivity; immunoglobulin; selection; somatic hypermutation