Autoimmune NZB/NZW F1 mice utilize B cell receptor editing for generating high‐affinity anti‐dsDNA autoantibodies from low‐affinity precursors

Abstract

We have previously constructed knock-in (C57BL/6×BALB/c) F1 mice, each expressing an anti-DNA heavy (H) chain (D42), combined with one of three different light (L) chains, namely V ‹ 1-J ‹ 1, V ‹ 4-J ‹ 4 or V ‹ 8-J ‹ 5. All of these H/L chain combinations bind DNA with similar affinity and fine specificity. However, while mice carrying V ‹ 1-J ‹ 1-transgenic L chain were tolerized almost exclusively by L chain receptor editing, the mice expressing V ‹ 8-J ‹ 5 L chains utilized clonal anergy as their principal mechanism of B cell tolerance. V ‹ 4-J ‹ 4 targeted mice exhibited an intermediate phenotype. In the present study, these three H/L chain combinations were backcrossed onto the autoimmune NZB/NZW F1 mice. We find that the mechanism of clonal anergy is abrogated in these mice, but that receptor editing is maintained. Moreover, diseased NZB/NZW mice utilize L chain secondary rearrangements for the generation of high-affinity, anti-dsDNA-producing B cells from low-affinity precursors. The edited B cell clones are not deleted or anergized in the autoimmune animal; rather they are selected for activation, class-switching and affinity maturation by somatic mutation. These results suggest that B cell receptor editing plays an important role not only in tolerance induction, but also in generating high-affinity autoreactive B cells in autoimmune diseases.

Peripheral B cell receptor editing may promote the production of high‐affinity autoantibodies in CD22‐deficient mice

“…In the BM, self DNA is likely to serve exclusively as a tolerogen for autoreactive B cells; in the spleen, however, the combination of genetic susceptibility, T cell help and elements of innate immunity (e.g. LPS and CpG-rich bacterial DNA) may convert self DNA into a potent immunogen.Our model differs from the two models suggested recently by Verkoczy et al [67] in that (1) the BM cells which are candidates for autoimmunity in our model are the low-affinity autoreactive B cells, and (2) our model does not entail any defective tolerance mechanism in the BM; rather, our previous [28] and present studies suggest that receptor editing is intact in autoimmune mouse models of SLE and that the autoimmune genetic background may primarily affect the activation phase of anti-DNA-autoreactive B cells. …”

“…3A). The two H/L combinations have very similar affinities and fine-specificities for DNA [21].B cells expressing the Vj1-Jj1 L chain in combination with the D42H chain had been shown to edit their L chain very efficiently while those expressing Vj8-Jj5 were largely resistant to secondary rearrangements [21,28]. Analysis of hybridoma mAb prepared from CD22 -/-D42H/Vj8-Jj5 mice confirms this observation (Fig.…”

“…3B); over 90% of hybridomas have retained their targeted Vj8-Jj5 L chain configuration. However, similarly to NZB/NZW double-Tg mice [28], a small fraction of CD22 -/-D42H/Vj8-Jj5 B cells have switched to IgG and accumulated somatic mutations (data not shown), reflecting the hyperactivation induced by the CD22 -/-mutation. In contrast, about 50% of CD22 -/-D42H/Vj1-Jj1 hybridomas have edited their Vj1-Jj1 L chain (Fig.…”

“…In the case of D42H/Vj1-Jj1-Tg mice, this peripheral editing process leads to the production of high-affinity anti-DNA D42H/VjRF-Jj5-expressing B cells and is not limited to the autoimmune CD22-deficient animals, as shown in Fig. 4.However, only in these mutant mice, as well as in the autoimmune NZB/NZW mice [28], the pathologic consequences of peripheral receptor editing are fully realized, as the edited anti-DNA D42H/VjRF-Jj5-expressing B cells are activated in these animals, class-switched, and proceed to antibody-secreting plasma cells (Fig. 3).…”

“…The ability of autoreactive B cells to edit their receptors was relatively independent of antigen affinity [21,25] but was largely dependent on the availability of unrearranged Jj minigenes in the transgenic (Tg) L chain [21,26]. Non-editing anti-DNA B cells were functionally inactivated (anergized) and this process was dependent on antigen affinity [20,21].In contrast, the same transgenes gave rise to a lupuslike anti-DNA response when expressed on the NZB/ NZW background with concomitant class switching and affinity maturation by somatic hypermutation [27,28]. A striking feature of the Tg anti-DNA antibodies in the diseased animals was the utilization of a unique endogenous L chain, VjRF-Jj5.…”