The change of Siglec-9 expression in peripheral blood NK cells of SFTS patients can affect the function of NK cells.

Objectives: To investigate the changes and mechanism of Siglec-9 on NK cells in peripheral blood of patients with severe fever with thrombocytopenia syndrome (SFTS).

Methods: First, we used single-cell RNA sequencing to analyze the frequency of NK cells in Peripheral Blood Mononuclear Cells (PBMCs) of SFTS patients and healthy controls (HCs), as well as the differences in the genes on NK cells. Secondly, we analyzed the expression of Siglec-9 and other receptors on NK cells by flow cytometry. Thirdly, we analyzed the correlation between Siglec-9 on NK cells and DBV viral load in plasma.

Results: Compared with HCs, the frequency of NK cells in peripheral blood of SFTS patients was significantly decreased, and the activating receptors on NK cells were reduced. The expression of Siglec-9 on NK cells and the frequency of Siglec-9NK cells decreased significantly in SFTS patients. The expression of Siglec-9 on CD16CD56 NK cells was negatively correlated with DBV viral load. In addition, Siglec-9NK cells expressed higher levels of activating receptors and exhibited stronger effector functions than Siglec-9NK cells.

Conclusions: The decreased expression of Siglec-9 on NK cells predicts NK cell dysfunction in SFTS patients, suggesting that Siglec-9 may be a potential marker for functional NK cell subsets in SFTS patients.