Generation of High-Affinity Antibody against T Cell-Dependent Antigen in the Ganp Gene-Transgenic Mouse

Generation of high-affinity Ab is impaired in mice lacking germinal center-associated DNA primase (GANP) in B cells. In this study, we examined the effect of its overexpression in ganp transgenic C57BL/6 mice ( Ganp Tg ). Ganp Tg displayed normal phenotype in B cell development, serum Ig levels, and responses against T cell-independent Ag; however, it generated the Ab with much higher affinity against nitrophenyl-chicken gammaglobulin in comparison with C57BL/6. To further examine the affinity increase, we established hybridomas producing high-affinity mAbs and compared their affinities using BIAcore. C57BL/6 generated high-affinity anti-nitrophenyl mAbs ( K D ∼ 2.50 × 10 −7 M) of IgG1/λ1 and contained the V H 186.2 region with W33L mutation. Ganp Tg generated much higher affinity ( K D > 1.57 × 10 −9 M) by usage of V H 186.2 as well as noncanonical V H 7183 regions. Ganp Tg also generated exceptionally high-affinity anti-HIV-1 (V3 peptide) mAbs ( K D > 9.90 × 10 −11 M) with neutralizing activity. These results demonstrated that GANP is involved in V region alteration generating high-affinity Ab.