Endocrine Abstracts

Objectives: Graves’ disease (GD) arises from the stimulatory action of TSH receptor antibodies (TSH-RAb). The involvement of innate immune cells has been explored with contradictory results. Through natural cytotoxicity and production of cytokines, Natural Killer (NK) cells respond to various challenges and regulate other immune cells (dendritic cells, monocytes/macrophages, lymphocytes) either promoting or inhibiting their proliferation. NK cells are classified, based on CD56 and CD16 surface antigen expression, into high cytotoxic CD56^dimCD16⁺ and cytokine-secreting CD56^brightCD16^- NK subsets.

Methods: In this cross-sectional case-control study, we aimed to investigate peripheral NK cell frequency, subset distribution, phenotype and cytolytic function in GD patients enrolled at different stages of disease, compared with healthy controls (HCs). Flow cytometry assessed NK cell expression of activating (CD69, NKG2D, NKp30) and inhibitory (CD161, NKG2A) receptors, cytotoxic capacity (CD107a), and interferon (IFN)-γ release.

Results: A total of 128 patients were included (mean age 54±17 years, 77% females), comprising 60 GD patients at diagnosis (GD_ND), 37 GD patients at 6 months of thyrostatic treatment (GD_6m), 9 at 15-18 months of treatment with negative TSH-RAb title (GD_18m), and 22 in remission (GD_r), and 82 HCs. Free thyroxine (FT4) levels were significantly and directly correlated with NK-CD69⁺ frequency and inversely with NK-CD107a⁺ (P < 0.001). In GD_ND, total NK and CD56^brightCD16^- cells were significantly higher than in HCs and other GD groups as were CD69⁺ cells. Compared to HCs, NK-CD16⁺ and NKp30⁺ NK cells were significantly more frequent in GD, while NK-CD161⁺ NK cells were lower (P < 0.05). In HCs, total and CD56^brightCD16^- cells expressing NKG2D⁺ were significantly higher compared to GD_ND and GD_6m, while the frequency of NKG2A⁺ cells was significantly lower compared to GD_ND. Percentages of NK-CD107a⁺ and NK-IFN-γ⁺ cells were lower (P < 0.05) in GD_ND compared to HCs.

Conclusion: At GD onset, the frequency of NK cells, especially those expressing activating receptors, was significantly higher than in HCs, GD patients under thyrostatic drugs, and in remission GD. This suggests NK cells may contribute to GD onset and progression. However, lower levels of NK cells expressing the cytotoxic marker CD107a and IFN-γ support an alternative hypothesis: increased activated NK cells may compensate for impaired cytotoxic activity, potentially limiting inflammation. Normalization of thyroid function correlated with reduced circulating NK cells, particularly activated subsets. These preliminary results suggest NK cell dysfunction involvement in GD pathogenesis may identify potential therapeutic targets for inflammation regulation.