A recurrent clonotype in the spontaneous anti-IgG2a rheumatoid factor response of lpr/lpr mice.

We generated mice transgenic for a VH gene that partially encodes an anti-IgG2a rheumatoid factor. Such transgenic VH genes recombine at a low frequency with the endogenous Igh locus in mice, giving rise to a small number of B cells that express heavy chains partially encoded by the transgene. The transgenes were crossed onto an lpr/lpr background, and hybridomas were generated from the resulting mice at 3 to 6 mo of age. Analysis of the anti-IgG2a- producing hybridomas obtained revealed that none expressed the transgenic VH. Surprisingly, however, most of the mice yielded multiple anti-IgG2a hybridomas that expressed VH genes comprised of a single VH gene segment, D regions with highly homologous 5' ends encoding CDR3 regions of identical length, and the JH4 segment. Expressed light chain diversity among these hybridomas was also highly restricted; most expressed a single V kappa gene segment. All of the hybridomas expressed members of the V kappa 19/28 family. Many of the VH genes contained a low frequency of somatic mutation. The recurrence of this family of V regions is not due to an indirect transgene effect or to effects of the genetic background used to construct the mice, as hybridomas expressing the predominant V gene segment combination were also isolated from a transgene-negative lpr/lpr littermate and from MRL lpr/lpr mice. These data contrast with the previous findings of others that while the spontaneous rheumatoid factor response of lpr/lpr mice was oligoclonal, recurrent clonotypes were not apparent, and the VH and V kappas encoding these rheumatoid factors contained a high frequency of somatic mutation whose distribution and type were indicative of Ag-driven selection.