Sustained humoral immunity in the patients recovered from severe fever with thrombocytopenia syndrome.

Background: Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne viral disease with a mortality rate of 10-30%; however, effective vaccines and therapies for this disease have not yet been developed. Understanding the long-term immune response of recovered individuals is critical for vaccine development and treatment. In this study, we conducted an epidemiological investigation of antibody and memory B cell trends in individuals with SFTS.

Methods: Peripheral blood mononuclear cells (PBMCs) and plasma were collected from 16 survivors of SFTS and five healthy controls. SFTS virus (SFTSV)-specific humoral immune responses were assessed using enzyme-linked immunosorbent assay (ELISA), biolayer interferometry (BLI), neutralization assays, and flow cytometry.

Results: SFTSV Gn-specific IgG was detected in plasma samples from all patients using ELISA and BLI. All patient plasma samples also presented neutralizing activity against SFTSV infection, and the IC₅₀ values were correlated with ELISA OD values (ρ = 0.700, P = 0.003 and BLI signals (ρ = 0.818, P = 0.0002). Neutralizing antibodies and SFTSV Gn-specific memory B cells were detected in samples from patients up to 6.7 years post-infection.

Conclusion: SFTSV-specific humoral immunity, including neutralizing antibodies and memory B cells, can persist in the majority of recovered patients, including those as late as 6.7 years post-infection. This information will be useful for the development of vaccines and antiviral therapies using antibodies against SFTS.