Immunoglobulin gene joints compensate for reduced on-rates imposed by somatic mutations in a V(H) gene.
Affinity maturation in the B lymphocyte response to a protein epitope appears to be largely due to a decrease in the off-rate constant of the antibodies (Ab) resulting from somatic mutation without a significant increase in the on-rate constant. Here, we show by site-directed mutagenesis of a germline encoded single-chain Fv that somatic mutations frequently selected in the Ab response to mouse cytochrome c (CYT) at heavy (H) chain positions 31 and 58 actually cause a two and three-fold decrease, respectively, in the on-rate constant as well as a two and five-fold decrease, respectively, in the off-rate constant and together cause nearly an eight-fold decrease in the off-rate. However, additional selection for a tyrosine residue at position 96 in the V(kappa)-J(kappa) joint compensates for the decreased on-rate imposed by the somatic mutations. This allows for an increase in the affinity of Ab during the secondary response. Certain sequences at the V(H)-D-J(H) joint were also shown to maintain a normal on-rate constant in the context of the common H chain mutations and, in addition, to reduce the off-rate, thus increasing the affinity. The results support the idea that both faster on-rates and slower off-rates for B lymphocyte antigen-specific receptors are favored during the maturation of the Ab response to mouse CYT.
Liu
J
J
Department of Microbiology and Center for Immunology, University of Minnesota Medical School, Box 196 Mayo Building, 420 Delaware Street S.E., Minneapolis, MN, 55455, USA.
Liu
L
L
Jemmerson
R
R
D000818:Animals; D000915:Antibody Affinity / Q000235:genetics*; D001402:B-Lymphocytes / Q000276:immunology*; D003574:Cytochrome c Group / Q000276:immunology; D005803:Genes, Immunoglobulin; D005854:Germ Cells; D007128:Immunoglobulin Fragments / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007135:Immunoglobulin Variable Region / Q000235:genetics*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D012641:Selection, Genetic
D003574:Cytochrome c Group; D007128:Immunoglobulin Fragments; D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region