Limiting HCDR3 diversity abrogates the antibody response to the bacterial polysaccharide α 1→3 Dextran (45.20)

Abstract

Anti-polysaccharide antibody responses in mice are often oligoclonal and the mechanisms involved in the production and subsequent antigen-driven selection of these clones are poorly understood. In this study, we investigated the α 1→3 Dextran (DEX) antibody response of gene-targeted mice limited to the usage of one DH gene segment (D-limited mice). We show that the DEX-specific antibody response is broadly comparable in D-limited mice to that of wild type BALB/c (WT) mice. D-limited mice forced to use DH reading frame 2 (ΔD-DµFS) showed both a higher total anti-DEX antibody response compared to other D-limited mice and the dominant DEX-specific J558 idiotype (Id) was higher compared to all mouse groups. Nucleotide sequencing of HCDR3s of DEX-specific plasmablasts showed that ΔD-DµFS mice generated 70% of clones similar to those from WT, including the predominant adult molecularly-determined clone J558. All three D-limited mouse groups showed a higher frequency of unusual DH-less HCDR3 regions compared to WT suggesting extensive junctional modification mediated by TdT. D-limited mice on TdT-deficient background failed to elicit a response to DEX. Overall, these data show that TdT activity is required to compensate for constraints on HCDR3 diversity for the generation of a normal anti-DEX antibody response by D-limited mice.