title: Antibody deficiency in patients with ataxia telangiectasia is caused by disturbed B- and T-cell homeostasis and reduced immune repertoire diversity.
abstract: BACKGROUND
  Ataxia telangiectasia (AT) is a multisystem DNA-repair disorder caused by mutations in the ataxia telangiectasia mutated (ATM) gene. Patients with AT have reduced B- and T-cell numbers and a highly variable immunodeficiency. ATM is important for V(D)J recombination and immunoglobulin class-switch recombination (CSR); however, little is known about the mechanisms resulting in antibody deficiency severity.
  
  
  OBJECTIVE
  We sought to examine the immunologic mechanisms responsible for antibody deficiency heterogeneity in patients with AT.
  
  
  METHODS
  In this study we included patients with classical AT plus early-onset hypogammaglobulinemia (n = 3), classical AT (n = 8), and variant AT (late onset, n = 4). We studied peripheral B- and T-cell subsets, B-cell subset replication history, somatic hypermutation frequencies, CSR patterns, B-cell repertoire, and ATM kinase activity.
  
  
  RESULTS
  Patients with classical AT lacked ATM kinase activity, whereas patients with variant AT showed residual function. Most patients had disturbed naive B-cell and T-cell homeostasis, as evidenced by low cell numbers, increased proliferation, a large proportion CD21(low)CD38(low) anergic B cells, and decreased antigen receptor repertoire diversity. Impaired formation of T cell-dependent memory B cells was predominantly found in patients with AT plus hypogammaglobulinemia. These patients had extremely low naive CD4(+) T-cell counts, which were more severely reduced compared with those seen in patients with classical AT without hypogammaglobulinemia. Finally, AT deficiency resulted in defective CSR to distal constant regions that might reflect an impaired ability of B cells to undergo multiple germinal center reactions.
  
  
  CONCLUSIONS
  The severity of the antibody deficiency in patients with AT correlates with disturbances in B- and T-cell homeostasis resulting in reduced immune repertoire diversity, which consequently affects the chance of successful antigen-dependent cognate B-T interaction.
authors.affiliation: Department of Pediatric Infectious Disease and Immunology, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: Gertjan J
authors.initials: GJ
authors.lastname: Driessen
authors.forename: Hanna
authors.initials: H
authors.lastname: Ijspeert
authors.forename: Corry M R
authors.initials: CM
authors.lastname: Weemaes
authors.forename: Ásgeir
authors.initials: Á
authors.lastname: Haraldsson
authors.forename: Margreet
authors.initials: M
authors.lastname: Trip
authors.forename: Adilia
authors.initials: A
authors.lastname: Warris
authors.forename: Michiel
authors.initials: M
authors.lastname: van der Flier
authors.forename: Nico
authors.initials: N
authors.lastname: Wulffraat
authors.forename: Mijke M M
authors.initials: MM
authors.lastname: Verhagen
authors.forename: Malcolm A
authors.initials: MA
authors.lastname: Taylor
authors.forename: Menno C
authors.initials: MC
authors.lastname: van Zelm
authors.forename: Jacques J M
authors.initials: JJ
authors.lastname: van Dongen
authors.forename: Marcel
authors.initials: M
authors.lastname: van Deuren
authors.forename: Mirjam
authors.initials: M
authors.lastname: van der Burg
mesh_terms: D000293:Adolescent; D000328:Adult; D000361:Agammaglobulinemia / Q000209:etiology / Q000235:genetics / Q000276:immunology; D001260:Ataxia Telangiectasia / Q000150:complications* / Q000235:genetics / Q000276:immunology*; D016175:B-Lymphocyte Subsets / Q000276:immunology*; D016022:Case-Control Studies; D002648:Child; D005260:Female; D006706:Homeostasis / Q000276:immunology*; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000209:etiology* / Q000235:genetics / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D016176:T-Lymphocyte Subsets / Q000276:immunology*