• Paulina Mertowska, Sebastian Mertowski, Wioleta Kowalska, Izabela Korona-Głowniak, and Ewelina Grywalska.
• Pol. Arch. Med. Wewn. 2024 Dec 19; 134 (12).

IntroductionEpstein‑Barr virus (EBV) reactivation is increasingly recognized as a potential exacerbator of autoimmune diseases, including Hashimoto thyroiditis (HT).ObjectivesThis study examined the association between EBV reactivation and intracellular Toll‑like receptor (TLR) expression in newly‑diagnosed, untreated HT patients. Its aim was to determine whether EBV reactivation and expression of specific TLRs (TLR3, TLR7, TLR8, and TLR9) contribute to the pathogenesis and progression of HT.Patients And MethodsThe study involved a cohort was 54 newly‑diagnosed, untreated patients with HT and 20 healthy volunteers (HVs) matched for age and sex. Blood samples were collected to assess EBV viral load and intracellular expression levels of TLR3, TLR7, TLR8, and TLR9 using flow cytometry. The levels of specific anti‑EBV antibodies (eg, viral capsid A [VCA] immunoglobulin [Ig] M, VCA IgG, Epstein‑Barr nuclear antigen 1 [EBNA‑1] IgM, EBNA‑1 IgG) were measured to identify signs of EBV reactivation, while soluble TLRs (sTLR3, sTLR7, sTLR8, and sTLR9) were quantified in serum using enzyme‑linked immunosorbent assay. Notably, our HT patients were not euthyroid, as they exhibited significantly lower thyroid‑stimulating hormone levels and elevated free triiodothyronine and free thyroxine levels in comparison with the HVs.ResultsThe study showed a significant increase in EBV reactivation among the HT patients, with 26 of 54 (48.1%) testing positive for EBV DNA, as compared with none of the HVs. The HT patients with reactivated EBV showed significantly higher intracellular expression of TLR3, TLR7, and TLR9, with TLR3+ cells constituting an average of 4.72% of CD4+ lymphocytes (vs 0.69% in the HVs), suggesting a potential synergistic effect. In addition, sTLR levels increased in the HT patients with reactivated EBV, suggesting a possible role of these receptors in potentiating autoimmune responses.ConclusionsThese findings highlight the importance of considering both viral reactivation and TLR activity in the treatment of HT. Understanding the interplay between EBV and intracellular TLRs may lead to development of new therapeutic approaches to mitigate the impact of these factors on the disease progression. Further research is warranted to investigate the mechanisms underlying this interaction and its implications for treatment strategies.

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