TLR4-MyD88-NF-κB signaling imbalances Th17 and Treg cells in thymoma with myasthenia gravis.

Thymus is an immune organ in which pathological changes may cause autoimmune diseases, including myasthenia gravis (MG). Recent studies have focused on Toll-like receptor 4 (TLR4) signaling as the cause of such changes. In our previous study, an imbalance of T helper 17 (Th17) cells and T regulatory (Treg) cells was found in MG thymoma. These results suggest the involvement of TLR4 in the pathogenesis of thymoma MG via an alteration of the Th17/Treg balance. Here, we aimed to assess whether the TLR4-MyD88-NF-κB pathway is upregulated in MG thymoma and its relationship with Th17/Treg cells. We collect thymoma samples from 54 patients with or without MG, detecting the expression level of TLR4, MyD88, and NF-κB in thymoma tissues. Next, we established an in vitro experiment of coculturing thymoma cells with CD4+ T cells and detected the differentiation of Th17 cells and Treg cells and their marker protein, retinoid-related orphan receptor gamma t (RORγt) and forkhead transcription factor 3 (Foxp3). We found TLR4, MyD88, and NF-κB expressed more in MG thymoma compared with simple thymoma. After the transwell coculturing, we observed an imbalance of Th17/Treg cells after TLR4 stimulation. TLR4 is stimulated in thymoma, causing an increase of Th17 cells and a decrease of Treg cells, namely an imbalance of Th17/Treg cells, resulting in MG.