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 similar to 2.50 X 10(-7) M) of IgG1/lambda 1 and contained the V(H)186.2 region with W33L mutation. GanpTg generated much higher affinity (K-D > 1.57 X 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, > 9.90 x 10-11 m) with neutralizing activity. These results demonstrated that GANP is involved in V region alteration generating high-affinity Ab.