Immunoglobulin class switch recombination is impaired in Atm-deficient mice.
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.
Lumsden
Joanne M
JM
Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bldg. 10, Room 4B10, 10 Center Dr., Bethesda, MD 20892, USA. lumsdenj@mail.nih.gov
McCarty
Thomas
T
Petiniot
Lisa K
LK
Shen
Rhuna
R
Barlow
Carrolee
C
Wynn
Thomas A
TA
Morse
Herbert C
HC
Gearhart
Patricia J
PJ
Wynshaw-Boris
Anthony
A
Max
Edward E
EE
Hodes
Richard J
RJ
D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D001402:B-Lymphocytes / Q000276:immunology*; D001483:Base Sequence; D018797:Cell Cycle Proteins; D017931:DNA Primers; D004260:DNA Repair; D004268:DNA-Binding Proteins; D004797:Enzyme-Linked Immunosorbent Assay; D005452:Fluoresceins; D006241:Haptens; D006433:Hemocyanins; D017578:Immunoglobulin Class Switching / Q000235:genetics* / Q000276:immunology; D007134:Immunoglobulin Switch Region / Q000235:genetics; D007136:Immunoglobulins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D016133:Polymerase Chain Reaction / Q000379:methods; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011995:Recombination, Genetic / Q000235:genetics* / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D027041:Somatic Hypermutation, Immunoglobulin / Q000235:genetics; D013388:Succinimides; D025521:Tumor Suppressor Proteins
C087165:5-(6)-carboxyfluorescein diacetate succinimidyl ester; D018797:Cell Cycle Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D005452:Fluoresceins; D006241:Haptens; D007136:Immunoglobulins; D013388:Succinimides; D025521:Tumor Suppressor Proteins; C054401:trinitrophenyl keyhole limpet hemocyanin; D006433:Hemocyanins; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D017346:Protein Serine-Threonine Kinases