The regulation of anti -double -stranded DNA B cells in healthy and autoimmune mice

A hallmark of systemic lupus erythematosus is the presence of anti-double-stranded (ds) DNA Abs that are absent in healthy individuals. To identify the mechanisms involved in the regulation of anti-dsDNA B cells in non-autoimmune mice and the steps leading to the production of these Abs in autoimmune mice, we have compared the phenotype and localization of anti-dsDNA B cells in autoimmune-prone (MRL+/+, MRL-lpr/lpr , and bcl-2 Tg) mice with that in non-autoimmune-prone (BALB/c) mice. To increase the frequency of anti-DNA B cells so that they can be identified and tracked, we have utilized a H-chain Tg that can pair with endogenous L-chains to generate anti-single-stranded (ss) DNA, anti-dsDNA, and non-DNA B cells, allowing us to study the regulation of anti-dsDNA B cells in the context of a diverse B cell repertoire. We have found that anti-dsDNA B cells are actively regulated in BALB/c mice as indicated by the lack of their Ig in the serum, their developmental arrest, increased turnover rate, and accumulation at the T/B interface of the splenic follicle. In the MRL genetic background, anti-dsDNA B cells are no longer developmentally arrested, suggesting an intrinsic B cell defect conferred by MRL background genes. With intact Fas, they continue to exhibit follicular exclusion; however, in the presence of the lpr/lpr mutation, anti-dsDNA B cells are now present in the follicle and their Ig becomes present in the serum. These data suggest that MRL mice are defective in maintaining the developmental arrest of autoreactive B cells and indicate a role for Fas in restricting entry into the follicle. In contrast, the presence of a bcl-2 Tg increased the lifespan of anti-dsDNA B cells, but did not alter the other features of tolerance. This suggests that the serum anti-dsDNA Abs present in bcl-2 Tg mice were not due to a breakdown in central tolerance, as was found for MRL-lpr/lpr mice. Instead, we provide evidence that these Abs originate from B cells that have transited a GC, in that they are somatically mutated and clonally expanded. Together these data directly show that a breakdown in the regulation of anti-dsDNA B cells can occur at two levels: in the generation of the primary repertoire in the BM or in the formation of the modified repertoire during GC maturation