Activation of Toll‐like receptor 4 by thyroid hormone triggers abnormal B‐cell activation

OBJECTIVE: Breakdown of tolerance and abnormal activation of B cells is an important mechanism in the pathogenesis of Graves' disease (GD). High levels of thyroid hormones (THs) play important roles in GD progression. However, the interactions between THs and abnormal activation of B cells remain elusive. This study aimed to explore the effect of high levels of THs on TLR4 expression and abnormal B cell differentiation. MATERIALS AND METHODS: Blood samples were collected from patients with GD and healthy controls (HCs) to evaluate the frequency of B cells, their subsets, and TLR4 expression in B cells. A high‐level T3 mouse model was used to study the interaction between THs and the TLR4 signalling pathway. RESULTS: We found that the frequencies of CD19(+), CD19(+) TLR4(+), CD19(+) CD86(+), and CD19(+) CD138(+) B cells were significantly higher, as were the expression levels of MRP8/MRP14 and MRP6 and MRP8, MRP14, and MRP6 messenger RNA (mRNA) in peripheral blood mononuclear cells in patients with GD. In high‐level T3 mice models, the serum MRP8/MRP14 and MRP6 levels and the TLR4 mRNA expression in PBMCs were significantly higher. TLR4 mRNA, protein expression, and cytokines downstream of TLR4, such as myeloid differentiation factor 88 (MyD88) and nuclear transcription factor‐κB, were also increased in mouse spleen mononuclear cells. CONCLUSION: The present study indicated that high levels of T3 can induce abnormal differentiation and activation of B cells by promoting TLR4 overexpression and provide novel insights into the roles of THs in the pathogenesis of GD.