Influence of AIRE-dependent versus -independent tissue restricted antigen expression by medullary thymic epithelial cells on T cell tolerance

Abstract

Abstract Thymocytes with high reactivity to self-antigens are, in large part, rendered tolerant through a number of mechanisms including clonal deletion and diversion toward regulatory T cell fates. Medullary thymic epithelial cells (mTECs) contribute to self-tolerance via the expression of tissue restricted antigens (TRAs). AIRE is responsible for the expression of approximately one third of TRAs, whereas AIRE-independent expression of TRAs by mTECs is less well characterized. To identify differences in AIRE-dependent and -independent tolerance, we generated new transgenic mouse models expressing a modified OVA-GFP fusion protein that contains several additional, well-characterized epitopes (2W, LCMV gp33 and LCMV gp66) in an AIRE-dependant or -independent manner. These models have enabled us to characterize distinct modes of tolerance for both MHC class I and II-restricted T cells in response to model peptides directed by AIRE-dependent and -independent TRA expression. Using organotypic culture of thymic slices overlaid with antigen-specific TCR transgenic thymocytes as well as tetramer analysis of the endogenous polyclonal T cell populations, we observed both antigen expression and peptide-specific differences in thymic selection. In addition, these difference lead to distinct levels of response to pathogen challenge and we are currently investigating the cellular interactions in the thymus associated with AIRE-dependent and -independent TRA induced tolerance by two-photon microscopy. These studies will lead to a better understanding of T cell tolerance mechanisms, and, in the longer term, inform the design of improved treatments for autoimmune diseases and cancer immunotherapies.