Multiple tolerance checkpoints prevent self-reactive lymphocytes from attacking self. When two such checkpoints were crippled by crossing Aire-deficient mice, which have a profound defect in thymic deletion, to Cblb-/- mice, which display a defect in T cell anergy, the offspring develop an infant-lethal autoimmunity directed exclusively against the exocrine pancreas and salivary glands. We hypothesize that the spectrum of organs targeted in this mouse model is dependent upon unique autoimmune “driver” T cell clones that are normally regulated by Aire and Cblb dependent tolerance mechanisms. To test this hypothesis, we first enriched for potential pathogenic clones by adoptively transferring Aire-/-Cblb-/- splenocytes into lymphopenic hosts. Next, we sorted individual CD4+ and CD8+ T cells from the adoptive transfer recipients and amplified transcripts encoding the TCRα and TCRβ chains using a novel multiplex RT-PCR strategy. Analysis of the T cell repertoire revealed a striking expansion of two dominant CD8+ clones representing 90% and 50% of the repertoire in the pancreas, and spleen, respectively.
TCR retrogenic mice expressing the TCR of the dominant pancreas-infiltrating CD8+ clone were able to cause pancreatitis and cachexia even in mice that were Aire and Cblb sufficient. To detect the normal frequency of this particular T cell clone in an unmanipulated environment, next generation sequencing of the TCRα and TCRβ repertoire of CD8+ T cells isolated from peripheral lymphoid organs of Aire-/-Cblb-/- mice was performed. Deep sequencing revealed that the pathogenic TCRα chain is actually expressed at very low frequencies in both wild-type and Aire-/-Cblb-/- mice.
In this study, we have deconstructed and reconstructed the pancreas specific autoimmunity in the Aire-/-Cblb-/- mouse model by showing that extremely rare self-reactive CD8+ T cells with particular TCR specificities mediate the rapid but discrete pattern of organ specific autoimmunity directed towards the exocrine pancreas. These results highlight the stringent mechanisms of immune tolerance and the complex nature of the pathogenesis of organ-specific autoimmune disease.