Loss of tolerance in anti -double -stranded DNA B cells during the chronic graft -versus -host reaction

Anti-double-stranded (ds)DNA antibodies (Abs) are specific diagnostic markers of systemic lupus erythematosus (SLE) and are also implicated in kidney pathology. It has been shown that anti-dsDNA B cells are tolerized in nonautoimmune mice. The immunodysregulation that causes these cells to break tolerance is presumably one part of the fundamental defects of SLE. To characterize the responsible mechanisms, we used the chronic graft-versus-host (cGVH) model mediated by MHC class II differences. The induction of cGVH in two anti-DNA knock-in (KI) transgenic mouse models on nonautoimmune backgrounds resulted in tolerance breakdown. Our data indicate two stages of activation under cGVH: a non-specific stage affecting most splenic B-cells, and an antigen (Ag)-specific stage associated with the production of SLE-Abs. This latter, receptor-driven stage is specifically marked by oligoclonal B cell expansion and a high frequency of mutations in the anti-dsDNA B cell population. Data from hybridoma clones indicated that secondary rearrangements at the light (L) and heavy (H) chains played a crucial role in generating anti-dsDNA B cells: anti-dsDNA cells retaining the transgenic H chain showed a disproportionately high frequency of λ1 and Jκ5 usage while the others replaced the transgene with endogenous VH genes. This suggests, contrary to expectation, that secondary rearrangement may play a critical role not only in tolerizing but also in generating the autoreactive B cells implicated in SLE. Analysis of a specific anti-dsDNA population (λ+) showed that cGVH raised the activation status of these cells. Upregulation of molecules involved in T-B cell interaction, as well as the ability of these cells to move to the T cell area of the follicle, appeared to be important factors in tolerance breakdown here. These results begin to clarify the sequence of events that brings about B-cell tolerance loss in systemic autoimmunity