Patterns of Ig V region expression among neonatal hemagglutinin-responsive B cells. Evidence for non-random VH gene representation during later stages of development.

Hybridoma libraries were established whose specificities reflect those within the BALB/c hemagglutinin-responsive B cell repertoire at 1 or 2 wk of age. These libraries were generated through chronic immunization regimes that induce responses dominated by clonotypes available at the age of initial immunization. Dot blot analyses of cytoplasmic RNA from these hybridomas were performed to determine the Ig H chain V region (VH) families associated with the repertoire at each age. Although genes from most known VH families can generate hemagglutinin-specific antibodies, clonotypes prevalent during the first week of life disproportionately use VH7183 gene segments. In contrast, hybridomas representative of the repertoire in 2-wk-old individuals preferentially use VHS107, VH36-60, and VHX24 gene segments. These results demonstrate changes in VH gene family predominance that correlate with the age-related patterns of clonal emergence and turnover previously shown in the hemagglutinin-reactive B cell pool. Taken together, these findings suggest that the very early neonatal Ag-responsive B cell pool closely reflects preferential VH gene rearrangements within the pre-B cell compartment. Further, they suggest that either non-random strategies of VH gene expression, or selective clonal expansion strategies based on VH, operate even at later stages of development.