W30 - Underlying T Cell Receptor Methylation Defects in Type 1 Diabetes Associated with Quantitative Defects

The structural organization and signaling of the T cell receptor (TCR)/CD3 complex underlies T cell development. T cell maturation defects are associated with autoimmunity, suggesting an underlying TCR selection defect. To explore quantitative defects in the TCR/CD3 protein complex as a cause for altered TCR selection in autoimmunity, we compared TCR expression densities on CD4 T cells from subjects with type 1 diabetes (T1D) (n=80) and non-diabetic controls (n=37) and looked for possible underlying overmethylation in T1D. Significant quantitative defects in TCR and CD3 proteins were observed in CD4+ T cells from T1D vs controls. TCR complex genes and associated CD3 genes were overmethylated in T1D, resulting in downregulated cell surface expression. Evaluation of TCRαβ expression in CD4+ T cells at the protein level confirmed methylation patterns, showing that the population of TCRαβ+ cells was significantly reduced in T1D vs controls (p=0.005). The MFI density of TCRαβ antibody in T1D was also significantly decreased vs controls (p=0.01). All CD3 genes except CD3ε had hypermethylated patterns in T1D, confirmed by RNAseq analysis. Both the percentage CD4+ T cell population (p=0.04) and the MFI of CD3+ T cells (p=0.02) were reduced in T1D vs controls. Patients with T1D have quantitative defects in the TCR/CD3 protein complex, resulting in decreased expression. It is recognized that TCR triggering is affected by intermolecular distance (density) between TCR proteins; activation diminishes with increased proximity between TCR surface proteins. In T1D, this might be a novel mechanism for failed T cell selection leading to autoimmunity.