Multiple tolerance checkpoints restrain affinity maturation of B cells expressing the germline precursor of a lupus patient-derived anti-dsDNA antibody in knock-in mice

概要

〔目的(Purpose)〕
Anti-dsDNA antibodies are a hallmark of systemic lupus erythematosus and are highly associated with its exacerbation. Cumulative evidence has suggested that somatic hypermutation contributes to the high-affinity reactivity of anti-dsDNA antibodies. Our previous study demonstrated that these antibodies are generated from germline precursors with low-affinity ssDNA reactivity through affinity maturation and clonal expansion in patients with acute lupus. This raised the question of whether such precursors could be subject to immune tolerance.

〔方法ならびに成績(Methods/Results)〕
To address this, we generated a site-directed knock-in (KI) mouse line, G9gl, which carries germline-reverted sequences of the VⅡ-DⅡ-JⅡ and Vk-Jk regions of patient-derived, high-affinity anti-dsDNA antibodies. G9gl heterozygous mice had a reduced number of peripheral B cells, only 27% of which expressed G9gl B cell receptor ( BCR). The remaining B cells harbored non-KI allele-derived immunoglobulin heavy (IgH) chains or fusion products of upstream mouse VⅡ and the KI gene, suggesting that receptor editing through VⅡ replacement occurred in a large proportion of B cells in the KI mice. G9gl BCR-expressing B cells responded to ssDNA but not to dsDNA, and exhibited several anergic phenotypes, including reduced surface BCR and shortened life span. Furthermore, G9gl B cells were excluded from germinal centers (GC) induced by several conditions. In particular, following immunization with methylated bovine serum albumin-conjugated bacterial DNA, G9gl B cells occurred at a high frequency in memory B cells but not GC B cells or plasmablasts.

〔総括(Conclusion)]
Collectively, multiple tolerance checkpoints prevented low-affinity precursors of pathogenic anti-dsDNA B cells from undergoing clonal expansion and affinity maturation in GCs.