VH mutant rabbits lacking the VH1a2 gene develop a2+ B cells in the appendix by gene conversion-like alteration of a rearranged VH4 gene.
We investigated the molecular basis for the appearance of V(H)a2 allotype-bearing B cells in mutant Alicia rabbits. The mutation arose in an a2 rabbit; mutants exhibit altered expression of V(H) genes because of a small deletion encompassing V(H)1a2, the 3'-most gene in the V(H) locus. The V(H)1 gene is the major source of V(H)a allotype because this gene is preferentially rearranged in normal rabbits. In young homozygous ali/ali animals, the levels of a2 molecules found in the serum increase with age. In adult ali/ali rabbits, 20 to 50% of serum Igs and B cells bear a2 allotypic determinants. Previous studies suggested that positive selection results in expansion of a2 allotype-bearing B cells in the appendix of young mutant ali/ali rabbits. We separated appendix cells from a 6-wk-old Alicia rabbit by FACS based on the expression of surface IgM and a2 allotype. The VDJ portion of the expressed Ig mRNA was amplified from the IgM+ a2+ and IgM+ a2- populations by reverse transcriptase-PCR. The cDNAs from both populations were cloned and sequenced. Analysis of these sequences suggested that, in a2+ B cells, the first D proximal functional gene in Alicia rabbits, V(H)4a2, rearranged and was altered further by a gene conversion-like mechanism. Upstream V(H) genes were identified as potential gene sequence donors; V(H)9 was found to be the most frequently used gene donor. Among the a2- B cells, y33 was the most frequently rearranged gene.
Sehgal
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Molecular Immunogenetics Section, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892, USA.
Mage
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Schiaffella
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D000595:Amino Acid Sequence; D000818:Animals; D000916:Antibody Diversity / Q000235:genetics; D001065:Appendix / Q000166:cytology / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D001483:Base Sequence; D005434:Flow Cytometry; D005785:Gene Conversion / Q000276:immunology*; D015326:Gene Rearrangement, B-Lymphocyte, Heavy Chain / Q000276:immunology*; D005803:Genes, Immunoglobulin; D007126:Immunoglobulin Allotypes; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007075:Immunoglobulin M / Q000235:genetics; D007135:Immunoglobulin Variable Region / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D011817:Rabbits; D017422:Sequence Analysis, DNA
D007126:Immunoglobulin Allotypes; D007143:Immunoglobulin Heavy Chains; D007075:Immunoglobulin M; D007135:Immunoglobulin Variable Region