Detection and evaluation of immunofunction of patients with severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus (SFTSV) with a high fatality rate. But the immunofunction was still unclear. The objective of our study was to assess the immunofunction in SFTS patients. Immunofunction test with flow cytometry which contains CD3+, CD4+ and CD8+ T lymphocytes, B cells and NK cells would be used for detecting serum samples collected from 34 SFTS cases and 20 healthy donors. We found that CD3+ and CD4+ T lymphocytes were significantly diminished in SFTS compared to normal control. In contrast, the percentage of NK cells was elevated. Further analysis revealed that the number of CD3+ and CD4+ T lymphocytes showed that there was a more robust pattern of depression in acute phase and severe SFTS infection compared to the patients in recovery phase and mild SFTS infection. But NK cells were significantly increased in acute phase and severe SFTS. They reverted to the near normal levels in convalescent phase. Additionally, the levels of CD3+ and CD4+ T lymphocytes progressively decreased in death group when compared with the survival group, but the level of B cells was higher. The damages of immune system were obvious, and the immune dysfunction might be partly responsible for disease progression of patients with SFTSV infection.