PREFERENTIAL V-H GENE USAGE IN RABBIT IG-SECRETING HETEROHYBRIDOMAS

B cells from leukemic rabbits preferentially use a single V-H gene, V( H)1, in their VDJ gene rearrangements. To determine whether Ig-secreti ng B cells from normal rabbits also preferentially use V(H)1, we gener ated rabbit x mouse heterohybridomas that stably secreted rabbit Ig th at expressed V(H)a allotypic specificities and analyzed the V-H genes used in their VDJ gene rearrangements. We cloned the VDJ genes from ni ne heterohybridomas, and by comparing the restriction map of the DNA i mmediately 5' of the translational start site of these VDJ genes to th at of the same region 5' of V(H)1, we showed that eight of the nine he terohybridoma clones use V(H)1. Comparison of the nucleotide sequences of the eight V(H)1-using VDJ genes with the nucleotide sequence of ge rm-line V(H)1 showed that each of them had somatically diversified. Th e diversified regions included clustered nucleotide changes and codon insertions and deletions, such as would be expected if the diversifica tion process involved somatic gene conversion. We searched our databas e of germ-line V-H genes for genes that could serve as donors for the gene conversion events, and we identified potential V-H donor genes fo r five regions of diversification. One of these regions of diversifica tion spanned at least 132 bp and included a codon insertion as well as 15 nucleotide changes. The data confirm that Ab diversity may be gene rated by a somatic gene conversion-like mechanism. The results directl y demonstrate that Ig-secreting B cells from normal rabbits preferenti ally use V(H)1 in their VDJ gene rearrangements.