title: Low-affinity IgM antibodies lacking somatic hypermutations are produced in the secondary response of C57BL/6 mice to (4-hydroxy-3-nitrophenyl)acetyl hapten.
abstract: Class-switched memory B cells, which are generated through the processes of somatic hypermutation (SHM) and affinity-based selection in germinal centers, contribute to the production of affinity-matured IgG antibodies in the secondary immune response. However, changes in the affinity of IgM antibodies during the immune response have not yet been studied, although IgM(+) memory B cells have been shown to be generated. In order to understand the relationship between IgM affinity and the recall immune response, we prepared hybridomas producing anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) IgM antibodies from C57BL/6 mice and from activation-induced cytidine deaminase (AID)-deficient mice. Binding analysis by ELISA showed that mAbs obtained from the secondary immune response contained IgM mAbs with affinity lower than the affinity of mAbs obtained from the primary response. By analyzing sequences of the IgM genes of hybridomas and plasma cells, we found many unmutated VH genes. VH genes that had neither tyrosine nor glycine at position 95 were frequent. The repertoire change may correlate with the lower affinity of IgM antibodies in the secondary response. The sequence and affinity changes in IgM antibodies were shown to be independent of SHM by analyzing hybridomas from AID-deficient mice. A functional assay revealed a reciprocal relationship between affinity and complement-dependent hemolytic activity toward NP-conjugated sheep RBCs; IgM antibodies with lower affinities had higher hemolytic activity. These findings indicate that lower affinity IgM antibodies with enhanced complement activation function are produced in the secondary immune response.
authors.affiliation: Laboratory of Structural Immunology, Division of Bioinformatics, Research Institute for Biomedical Sciences (RIBS), Tokyo University of Science, Chiba 278-0022, Japan.
authors.forename: Akikazu
authors.initials: A
authors.lastname: Murakami
authors.forename: Hayato
authors.initials: H
authors.lastname: Moriyama
authors.forename: Mina
authors.initials: M
authors.lastname: Osako-Kabasawa
authors.forename: Kanako
authors.initials: K
authors.lastname: Endo
authors.forename: Miyuki
authors.initials: M
authors.lastname: Nishimura
authors.forename: Keiko
authors.initials: K
authors.lastname: Udaka
authors.forename: Masamichi
authors.initials: M
authors.lastname: Muramatsu
authors.forename: Tasuku
authors.initials: T
authors.lastname: Honjo
authors.forename: Takachika
authors.initials: T
authors.lastname: Azuma
authors.forename: Takeyuki
authors.initials: T
authors.lastname: Shimizu
mesh_terms: D000818:Animals; D000915:Antibody Affinity; D000920:Antibody-Dependent Cell Cytotoxicity / Q000235:genetics; D001402:B-Lymphocytes / Q000276:immunology*; D003564:Cytidine Deaminase / Q000235:genetics; D006241:Haptens / Q000276:immunology; D006825:Hybridomas; D007117:Immunization, Secondary; D007075:Immunoglobulin M / Q000378:metabolism*; D007156:Immunologic Memory; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009596:Nitrophenols / Q000276:immunology; D010648:Phenylacetates / Q000276:immunology; D010950:Plasma Cells / Q000276:immunology*; D011485:Protein Binding; D061905:Single-Domain Antibodies / Q000235:genetics; D027041:Somatic Hypermutation, Immunoglobulin; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D006241:Haptens; D007075:Immunoglobulin M; D009596:Nitrophenols; D010648:Phenylacetates; D061905:Single-Domain Antibodies; C026242:4-hydroxy-5-nitrophenyl acetic acid; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase
keywords: affinity maturation; antibody; memory B cell; plasma cell; somatic hypermutation