The Importance of Myeloid-Derived Suppressor Cells in the Regulation of Immunosuppressive Mechanisms by Severe Fever with Thrombocytopenia Syndrome

Objective: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus (SFTSV) with a high fatality rate. The objective of our study was to assess the mechanisms of immunofunction through detecting the presence of myeloid-derived suppressor cells (MDSC), granulocyte-colony stimulating factor (G-CFS) and T cells in SFTS patients. Methods: Serum samples from 30 SFTS cases and 20 healthy donors were collected for the test with flow cytometry and sandwich ELISA which contains CD3+, CD4+ T lymphocytes, subsets of MDSC and G-CSF. Results: Granulocytic MDSC (G-MDSC) and monocytic MDSC (M-MDSC) were significantly elevated in SFTS compared to normal control, and G-CSF was expressed at increased frequency. In contrast, CD3+ and CD4+ T lymphocytes were significantly diminished. Further analysis revealed that G-MDSC and G-CSF were higher in severe SFTS infection compared to the patients in mild SFTS infection, and the numbers of CD3+ and CD4+ T lymphocytes showed a more robust pattern of depression. Conclution: In summary, we have characterized an immunosuppressive mechanism in SFTSV infection dependent on G-CSF induction on MDSC and MDSC suppressing T cells