The efficiency of B cell receptor (BCR) editing is dependent on BCR light chain rearrangement status

Abstract

Anti-DNA knock-in mice serve as models for studying B cell tolerance mechanisms to a ubiquitous antigen. We have constructed six strains of double transgenic (C57BL/6xBALB/c)F1 mice, each expressing an unmutated or somatically mutated anti-DNA heavy (H) chain, combined with one of three different light (L) chains, namely V(kappa)1-J(kappa)1, V(kappa)4-J(kappa)4 and V(kappa)8-J(kappa)5. In vitro analysis of the various Ig H/L chain combinations showed that all had a similar specificity for single-stranded DNA and double-stranded DNA, but that antibodies encoded by the mutated H chain had higher affinities for the autoantigen. None of the targeted mouse strains exhibited significant levels of serum anti-DNA activity. However, while B cells from mice carrying the V(kappa)1-J(kappa)1 transgenic L chains were tolerized almost exclusively by L chain receptor editing in an affinity-independent manner, the mice expressing V(kappa)8-J(kappa)5 L chains have utilized affinity-dependent clonal anergy as their sole mechanism of B cell tolerance. V(kappa)4-J(kappa)4 targeted mice exhibited an intermediate phenotype with respect to these two mechanisms of B cell tolerance. Our results suggest that receptor editing is the preferred mechanism of B cell tolerance and that the efficiency of L chain editing is directly related to the number of available J(kappa) segments on the expressed V(kappa) allele.

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

“…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.…”

“…This defect is associated with a reduced surface expression of CD22 on resting B cells and reduced ability of LPS-activated B cells to up-regulate CD22. Therefore, data from the CD22-knockout mice link defects in CD22 expression to the development of autoimmunity [18,19].We have now extended these pioneering studies by utilizing our well-defined anti-DNA knock-in mouse lines, in which a single anti-DNA H chain (D42H of the NZB/NZW anti-DNA D42 hybridoma) or combinations of this H chain with different L chains (Vj1-Jj1 or Vj8-Jj5) have been targeted to the appropriate chromosomal loci in the mouse genome [20,21]. When expressed on a non-autoimmune mouse background, no anti-DNA activity was found in the serum of H chain-or H/L chain-targeted mice and the animals showed features of all three known mechanisms of B cell tolerance, i.e.…”

“…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.…”

“…Examples from DNA-binding and -nonbinding hybridomas were subjected to further analysis. The great majority of DNA-binding mAb carried the b allotype-positive, Tg D42H chain, while a much smaller proportion of non-DNA binding mAb were Tgpositive (Table 1), and expressed an endogenous H chain, possibly due to a spontaneous or editinginduced inactivation of the targeted D42H gene [20,21]. Fig.…”

“…In these mouse models, central B cell tolerance may be intact, similarly to non-autoimmune animals, in which non-edited, high-affinity anti-DNA-expressing immature B cells are centrally deleted in the BM very efficiently [32]. The question is, then, whether some high-affinity autoreactive B cells can escape central deletion in the BM and arrive at peripheral lymphoid organs, where they may be abnormally activated by the products of the specific B cell modifying genes as in the case of CD22 -/-or BAFF-Tg mice, or by excessive T cell help in the case of cGVH mice.The second, non-mutually exclusive possibility is that central tolerance to high-affinity autoreactive B cells in these mouse models is essentially intact, but low-affinity autoreactive B cells, which are known to escape central deletion by anergy [21,45] or by ignorance [46], are subject to receptor editing in the periphery. Some of these cells may then acquire very high affinity for the autoantigen and subsequently be recruited to the mature autoreactive B cell pool in the diseased animal.…”