Immunoglobulin class switch recombination is impaired in Atm-deficient mice

• Published in: The Journal of experimental medicine 2004-11, Vol.200 (9), p.1111-1121
• Main Authors: Lumsden, Joanne M, McCarty, Thomas, Petiniot, Lisa K, Shen, Rhuna, Barlow, Carrolee, Wynn, Thomas A, Morse, 3rd, Herbert C, Gearhart, Patricia J, Wynshaw-Boris, Anthony, Max, Edward E, Hodes, Richard J
• Format: Article
• Language: English
• Subjects: Animals; Ataxia Telangiectasia Mutated Proteins; B-Lymphocytes - immunology; Base Sequence; Cell Cycle Proteins; DNA Primers; DNA Repair; DNA-Binding Proteins; Enzyme-Linked Immunosorbent Assay; Fluoresceins; Haptens; Hemocyanins; Immunoglobulin Class Switching - genetics; Immunoglobulin Class Switching - immunology; Immunoglobulin Switch Region - genetics; Immunoglobulins - genetics; Immunoglobulins - metabolism; Mice; Mice, Mutant Strains; Polymerase Chain Reaction - methods; Protein-Serine-Threonine Kinases - genetics; Recombination, Genetic - genetics; Recombination, Genetic - immunology; Reverse Transcriptase Polymerase Chain Reaction; Sequence Analysis, DNA; Sequence Homology; Somatic Hypermutation, Immunoglobulin - genetics; Succinimides; Tumor Suppressor Proteins
• ISSN: 0022-1007; 1540-9538; 1892-1007
• DOI: 10.1084/jem.20041074

Immunoglobulin class switch recombination (Ig CSR) involves DNA double strand breaks (DSBs) at recombining switch regions and repair of these breaks by nonhomologous end-joining. Because the protein kinase ataxia telengiectasia (AT) mutated (ATM) plays a critical role in DSB repair and AT patients show abnormalities of Ig isotype expression, we assessed the role of ATM in CSR by examining ATM-deficient mice. In response to T cell-dependent antigen (Ag), Atm-/- mice secreted substantially less Ag-specific IgA, IgG1, IgG2b, and IgG3, and less total IgE than Atm+/+ controls. To determine whether Atm-/- B cells have an intrinsic defect in their ability to undergo CSR, we analyzed in vitro responses of purified B cells. Atm-/- cells secreted substantially less IgA, IgG1, IgG2a, IgG3, and IgE than wild-type (WT) controls in response to stimulation with lipopolysaccharide, CD40 ligand, or anti-IgD plus appropriate cytokines. Molecular analysis of in vitro responses indicated that WT and Atm-/- B cells produced equivalent amounts of germline IgG1 and IgE transcripts, whereas Atm-/- B cells produced markedly reduced productive IgG1 and IgE transcripts. The reduction in isotype switching by Atm-/- B cells occurs at the level of genomic DNA recombination as measured by digestion-circularization PCR. Analysis of sequences at CSR sites indicated that there is greater microhomology at the mu-gamma1 switch junctions in ATM B cells than in wild-type B cells, suggesting that ATM function affects the need or preference for sequence homology in the CSR process. These findings suggest a role of ATM in DNA DSB recognition and/or repair during CSR.