Recirculating bone marrow B cells in C57BL/6 mice are more tolerant of highly hydrophobic and highly charged CDR-H3s than those in BALB/c mice

To test whether mechanisms controlling the range of diversity of the developing antibody repertoire in C57BL/6 mice (IgH^b) operate similarly to those identified in BALB/c mice (IgH^a), we compared the sequences of V_H7183-containing H-chain transcripts from sorted adult bone marrow C57BL/6 B-cell subsets with those previously obtained from BALB/c mice. Patterns of VDJ gene segment utilization and CDR-H3 amino acid composition, charge, and average length in C57BL/6 pro-B cells were similar, although not identical, to BALB/c pro-B cells. However, C57BL/6 mature, recirculating B cells failed to demonstrate the reduction in the use of VH81X and the narrowing in the range of variance of CDR-H3 hydrophobicity that characterizes B-cell maturation in BALB/c mice. To further test the ability of the C57BL/6 strain to discard B cells expressing highly charged CDR-H3s, we introduced a mutant IgH^a D_H allele that forces use of arginine, asparagine, and histidine. Unlike BALB/c mice, C57BL/6 mice congenic for the charged D_H maintained normal numbers of mature, recirculating B cells that were enriched for charged CDR-H3s. Together these findings indicate that the mature C57BL/6 B-cell pool permits expression of immunoglobulins with antigen-binding sites that are typically discarded during late-stage bone marrow B-cell development in BALB/c mice.