title: Genetics of the phosphocholine-specific antibody response to Streptococcus pneumoniae. Germ-line but not mutated T15 antibodies are dominantly selected.
abstract: The role that somatic mutations play in the phosphocholine-specific, antibody response to Streptococcus pneumoniae was examined by studying sets of hybridomas from different individual mice. As expected most of the cell lines were from the T15 anti-phosphocholine family and were not encoded by the v1 gene of the T15 VH family and V kappa 22. A minority of antibodies were from the M603 (v1/V kappa 8) and M511 (v1/V kappa 24) families. Three additional antibodies were encoded by the v11 gene of the T15 family; two were paired with a V lambda and the other with a V kappa 1 gene. In vitro binding studies showed that T15- and M603-like antibodies had the highest affinity for S. pneumoniae. Complete sequencing of the VH and VL mRNA from 25 of the hybridomas revealed somatic mutations in 11 of the antibodies. A total of 17 independently derived T15 positive cell lines were studied in detail, six of these were mutated. These mutations were scattered throughout the V regions and the replacement to silent ratio was typical of that for framework regions. Statistical evaluation of the placement of mutations showed that there was a slight but significantly decreased frequency of mutations in complementarity determining regions. Comparisons of mutated and unmutated T15-related antibodies showed that mutations caused a decrease in binding to S. pneumoniae in every case. These results argue that the optimal specificity for this molecular form of phosphocholine is encoded in the germline and that Ag-driven events favor selection of B cells expressing these germ-line encoded antibodies.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000907:Antibodies, Bacterial / Q000096:biosynthesis / Q000235:genetics*; D000911:Antibodies, Monoclonal / Q000235:genetics; D000918:Antibody Specificity; D001483:Base Sequence; D002794:Choline / Q000031:analogs & derivatives*; D005803:Genes, Immunoglobulin; D005854:Germ Cells / Q000276:immunology; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007130:Immunoglobulin Idiotypes / Q000235:genetics; D007147:Immunoglobulin Light Chains / Q000235:genetics; D007135:Immunoglobulin Variable Region / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D009194:Myeloma Proteins / Q000235:genetics* / Q000276:immunology; D010767:Phosphorylcholine / Q000276:immunology*; D013296:Streptococcus pneumoniae / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D007143:Immunoglobulin Heavy Chains; D007130:Immunoglobulin Idiotypes; D007147:Immunoglobulin Light Chains; D007135:Immunoglobulin Variable Region; D009194:Myeloma Proteins; C043925:myeloma protein TEPC15; D010767:Phosphorylcholine; D002794:Choline