To recapitulate this value in the B cell repertoires of CD45.1 mice, we transferred CD45.2 09-1B12-UCA B cells (H09-1B12-UCA/WT, 09-1B12-UCA/WT) at increasing amounts and then measured the VH1-18 QxxV bnAb precursor frequency (H3ssF+/H7ssF+/H3ssF-KO/H7ssF-KO) in the spleen of the recipient mice. Transfer of 100,000 09-1B12-UCA B cells reproducibly gave a value of 1 in 100,000 B cells (n= 5 recipient mice per transfer amount, one experiment), and consequently, this was the VH1-18 QxxV bnAb precursor frequency used in all subsequent immunization experiments.
