Co-operative failure of Aire-mediated clonal deletion and Cblb-mediated clonal anergy in the pathogenesis of autoimmunity
Creators: name: Teh, Charis En-Yi
Publisher: name: The Australian National University
Year: 2012
Subjects: subject: Autoimmune diseases Pathogenesis
subject: Autoimmunity
subject: Immunological tolerance
subject: T cells

description: Breakdown of self-tolerance in autoimmune diseases is poorly understood, as is the existence of so many different mechanisms for actively acquired tolerance. In this thesis, I find that failure of two tolerance mechanisms, thymic T cell clonal deletion to organ specific antigens mediated by Aire and the two-signal mechanisms of T cell tolerance in mature T cells imposed by the ubiquitin ligase Cblb, individually cause slow and subclinical autoimmunity but combine co-operatively to allow lethal T cell-mediated destruction of the exocrine tissue in the pancreas and salivary glands within weeks after T cells emerge from the thymus. Intriguingly, there was no evidence of autoimmunity in other tissues although Aire regulates deletion of T cells recognising huge numbers of self-antigens from multiple tissues. Varying the nascent T cell repertoire by substituting the B10.BR.H2k MHC in which the T cells were selected upon with the C57/B6.H2b MHC or introducing an unlimited source of transgenic T cells with a single specificity towards an alternative organ failed to redirect the autoimmunity in Aire-/-Cblb-/- mice to other organs, albeit these strategies slowed down the intensity and tempo of the disease. This indicated that there was a unique feature of the ""driver"" T cells that escaped tolerance in Aire-/-Cblb-/- mice. To illuminate the unique properties of the autoimmune driver cells in Aire-/-Cblb-/- mice, a new approach to isolate pancreas-specific T cell clones was successfully established. This involved enriching for the driver T cells by serial adoptive transfer, followed by RT-PCR amplification and sequencing of mRNAs encoding the paired TCRalpha and TCRbeta chains from single T cells sorted from the pancreas or spleen. A remarkably oligoclonal expansion of CD8 T cells within the pancreas was revealed, comprising several clones within an animal bearing highly related TCRs. The TCR from one of the expanded CD8 T cell clones, 3.5, was expressed in retroviral transgenic (retrogenic) bone marrow chimeras. T cells expressing TCR3.5 were positively selected into the CD8 T cell lineage, showed no evidence of negative selection in Aire-wild-type thymi, and accumulated as mature naive CD8 T cells in the axillary and inguinal lymph nodes. TCR3.5 CD8 T cells were nevertheless activated in the pancreatic lymph node and accumulated in the pancreas, and retrogenic expression of TCR3.5 was sufficient to precipitate extensive exocrine pancreatitis in animals with wild-type Aire and Cblb genes. These results suggest that Aire may not directly regulate the driver CD8 T cells, raising novel possibilities about how the defects in Aire and Cblb co-operate to precipitate organ-specific autoimmunity. These findings are the first to reveal a higher-level architecture assembling individual tolerance mechanisms for robust autoimmunity, establishing a multistep framework for understanding how individual mechanisms fit together for robust tolerance. Understanding how genetic defects in tolerance mechanism co-operate with each other is critical for interpreting patterns of genetic and phenotypic variability in human autoimmune diseases. -- provided by Candidate.