The B-cell repertoire in neonatal mice contains predominant clonotypes that are reproducibly expressed at particular times after birth. We have isolated and sequenced heavy and light chain cDNA clones from three 2,4-dinitrophenyl-specific neonatal hybridomas. Two of these hybridomas (TF2-36 and TF5-139) express idiotypes (Ids) that predominate during the first days after birth, and the third hybridoma (TF2-76) expresses Although the adult primary B-cell repertoire ofBALB/c mice exceeds 107 conotypes (1, 2), the antibody repertoire at birth is limited to 104-105 different specificities (3, 4). During the first weeks after birth, this repertoire undergoes a reproducible and patterned expansion (3-9). Thus, in the first 3 days of neonatal life, all BALB/c neonates share three predominant 2,4-dinitrophenyl (DNP)-specific and three predominant 2,4,6-trinitrophenyl (TNP)-specific clonotypes (3). The same mice do not express predominant clonotypes for fluorescein (3), phosphocholine (6), and either a(1-*3) or a(1--6) dextran determinants (7,8). Phosphocholine-specific clones reproducibly appear several days after DNP-or TNP-specific clones in both fetal liver (9) and neonatal spleen (6). Two weeks after birth, the antibody repertoire, which contains 106 specificities, is still more restricted than the adult repertoire (5).Recently, several investigators have attempted to correlate this patterned acquisition of the antibody repertoire with the preferential rearrangement of specific variable (V) region gene segments (10, 11). Murine germ-line heavy (H) chain V region gene segments (VH) have been grouped by sequence homologies into eight families (12, 13). VH recombinant strains have been used to obtain the order of these VH families, whose names relate to cell lines, on chromosome 12 as: 5' (VH 3609, VH 36-60, VH J606, VH X24)-VH J558-VH S107-VH Q52-VH 7183-D-JH 3' (14). The relative order ofthe set of VH gene families 5' to the J558 VH family cannot be mapped with the existing recombinant strains. The potential correlation between sequential rearrangement of V segments and sequential expression of antibody specificities is based on the observation that the rearrangement of VH families in fetal liver pre-B-cells is not random (10, 11). Cells with a rearranged member of the 7183 VH family have been the most frequently found among Abelson murine leukemia virus (Ab-MuLV)-transformed pre-B-cells and among fetal liver pre-B-cell hybridomas. This is especially striking because the 7183 VH family represents only z10% of all VH genes (13). One member of the 7183 VH family, VH 81X, rearranges at a particularly high frequency. VH 81X, one of the most JHproximal VH regions, is rearranged in almost half of AbMuLV-transformed fetal liver pre-B-cells (10).In order to evaluate the contribution of such a developmentally ordered rearrangement of V segments to the repertoire of antigen-responsive B cells, we have examined the V genes utilized by three hybridomas derived by fusion of DNP-hemocyanin-stimulated neonatal spleen cell...

Newly generated bone marrow B cell precursors of aged BALB/c mice, stimulated in splenic fragment cultures, display a markedly increased frequency of phosphorylcholine (PC)-responsive cells. This increased frequency is found for both precursors that utilize VHS107, a phenotype common to essentially all PC-specific B cells of young mice, and, surprisingly, for precursors that utilize VH genes other than VHS107. PC-specific hybridomas derived from bone marrow cells of aged mice utilize members of at least three VH gene segment families that have never been observed in PC responses of young mice. The ability of aged but not young mice to generate these unique PC-specific clonotypes may be evidence for constraints on V region utilization during repertoire development in young adults and has important implications for aging-associated changes in immune responsiveness.

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