Enhanced mutational activity and disturbed selection of mutations in V-H gene rearrangements in a patient with systemic lupus erythematosus

To determine the impact of somatic hypermutation and selective influences o n the V-H gene repertoire in SLE, the mutational frequency and pattern of m utations in nonproductively and productively rearranged V-H genes obtained from genomic DNA of individual CD19+ B cells were analyzed in a patient wit h SLE. The mutational frequencies of nonproductive (6.54x10(-2)) as well as of pro ductive (4.38x10(-2)) V-H rearrangements were significantly higher in the S LE patient than in normal controls (3.8x10(-2), p<0.001 and 3.3x10(-2); p<0 .001. respectively). Analysis of nonproductive rearrangements documented on ly minor abnormalities of the targeting of the mutator in the SLE patient. The majority of "mutational hot spots", although different than in normals, appeared in the CDRs and an increased frequency of mutations in RGYW/WRCY sequences was observed. Moreover, no biases in base pair changes were found in the nonproductive repertoire. In contrast, there was a selection against A and T mutations and towards G mutations within the productive repertoire. Importantly, there were no sign ificant differences in the R/S ratios of mutations within the FRs between t he nonproductive and productive repertoire consistent with abnormalities in elimination of B cells expressing V-H genes with these mutations. The resu lt of this abnormality was a significantly higher R/S ratio of the V-H gene s in the productive repertoire of the SLE patient compared to normals (p<0. 05). These data indicate that the mutational machinery was markedly enhanced in this SLE patient but exhibited nearly normal targeting, whereas selective i nfluences were abnormal. These findings suggest that both enhanced mutation al activity and disturbances in selection may have played a role in the eme rgence of autoreactivity in this SLE patient.