title: An activation-induced cytidine deaminase-independent mechanism of secondary VH gene rearrangement in preimmune human B cells.
abstract: V(H) replacement is a form of IgH chain receptor editing that is believed to be mediated by recombinase cleavage at cryptic recombination signal sequences (cRSS) embedded in V(H) genes. Whereas there are several reports of V(H) replacement in primary and transformed human B cells and murine models, it remains unclear whether V(H) replacement contributes to the normal human B cell repertoire. We identified V(H)-->V(H)(D)J(H) compound rearrangements from fetal liver, fetal bone marrow, and naive peripheral blood, all of which involved invading and recipient V(H)4 genes that contain a cryptic heptamer, a 13-bp spacer, and nonamer in the 5' portion of framework region 3. Surprisingly, all pseudohybrid joins lacked the molecular processing associated with typical V(H)(D)J(H) recombination or nonhomologous end joining. Although inefficient compared with a canonical recombination signal sequences, the V(H)4 cRSS was a significantly better substrate for in vitro RAG-mediated cleavage than the V(H)3 cRSS. It has been suggested that activation-induced cytidine deamination (AICDA) may contribute to V(H) replacement. However, we found similar secondary rearrangements using V(H)4 genes in AICDA-deficient human B cells. The data suggest that V(H)4 replacement in preimmune human B cells is mediated by an AICDA-independent mechanism resulting from inefficient but selective RAG activity.
authors.affiliation: Autoimmunity Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institute of Diabetes andDigestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-1560, USA.
authors.forename: Nancy S
authors.initials: NS
authors.lastname: Longo
authors.forename: Gabrielle J
authors.initials: GJ
authors.lastname: Grundy
authors.forename: Jisoo
authors.initials: J
authors.lastname: Lee
authors.forename: Martin
authors.initials: M
authors.lastname: Gellert
authors.forename: Peter E
authors.initials: PE
authors.lastname: Lipsky
mesh_terms: D000818:Animals; D002461:Cell Line, Transformed; D003564:Cytidine Deaminase / Q000172:deficiency / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000235:genetics / Q000276:immunology*; D007135:Immunoglobulin Variable Region / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008954:Models, Biological; D021382:Protein Sorting Signals / Q000235:genetics; D011995:Recombination, Genetic / Q000235:genetics / Q000276:immunology; D027041:Somatic Hypermutation, Immunoglobulin / Q000502:physiology*; D045567:VDJ Recombinases / Q000235:genetics / Q000276:immunology*; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; D021382:Protein Sorting Signals; D045567:VDJ Recombinases; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase