Predicted T-Cell and B-Cell Epitopes of NIS: Where Do Sjögren's Syndrome and Hashimoto's Thyroiditis Converge?

The sodium iodide symporter (NIS) is a key protein in thyroid function responsible for iodine uptake, and it may be involved in the pathogenesis of autoimmune thyroiditis. However, it is also expressed in the salivary glands, the primary target of autoreactive cells in Sjögren's syndrome (SS). Given the common link between the two diseases, we computationally investigated whether the epitopes of NIS can trigger an immune response leading to SS in Hashimoto's thyroiditis (HT) patients genetically predisposed to both diseases. The TepiTool 2016, ABCpred 2006, and DiscoTope 2.0 servers were used to predict T-cell and B-cell epitopes by inputting the FASTA sequences and 3D structures of NIS, thyroid peroxidase (TPO) and Ro60 Y RNA-binding protein (Ro60), which served as reference antigens for HT and SS, respectively. T-cell epitopes were selected based on their binding to a panel of human leukocyte antigen (HLA) alleles associated with both SS and HT. We identified a total of 376 linear T-cell epitopes, 64 linear B-cell epitopes and 68 conformational B-cell epitopes of NIS. Compared to TPO, NIS T-cell epitopes showed significantly lower affinity for HLA alleles (p < 0.0001), while no significant difference was found compared to Ro60. While linear B-cell epitopes of NIS, TPO, and Ro60 showed similar binding affinity, conformational epitopes of NIS were predicted to have higher immunogenicity than Ro60 (p = 0.04), while no significant difference was found compared to TPO. These pivotal findings, discovered by the methods of computer modeling, suggest that NIS can potentially activate T cells and B cells in patients with genetic predisposition to SS and HT and need to be confirmed by further laboratory studies.