Identification and characterization of three monoclonal antibodies targeting the SFTSV glycoprotein and displaying a broad spectrum recognition of SFTSV-related viruses.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel tick-borne viral pathogen that causes severe fever with thrombocytopenia syndrome (SFTS). The disease was initially reported in central and eastern China, then later in Japan and South Korea, with a mortality rate of 13-30%. Currently, no vaccines or effective therapeutics are available for SFTS treatment. In this study, three monoclonal antibodies (mAbs) targeting the SFTSV envelope glycoprotein Gn were obtained using the hybridoma technique. Two mAbs recognized linear epitopes and did not neutralize SFTSV, while the mAb 40C10 can effectively neutralized SFTSV of different genotypes and also the SFTSV-related Guertu virus (GTV) and Heartland virus (HRTV) by targeting a spatial epitope of Gn. Additionally, the mAb 40C10 showed therapeutic effect in mice infected with different genotypes of SFTSV strains against death by preventing the development of lesions and by promoting virus clearance in tissues. The therapeutic effect could still be observed in mice infected with SFTSV which were administered with mAb 40C10 after infection even up to 4 days. These findings enhance our understanding of SFTSV immunogenicity and provide valuable information for designing detection methods and strategies targeting SFTSV antigens. The neutralizing mAb 40C10 possesses the potential to be further developed as a therapeutic monoclonal antibody against SFTSV and SFTSV-related viruses.

Fine epitope mapping of glycoprotein Gn in Guertu virus.

Guertu virus (GTV) is a tick-borne phleboviruses (TBPVs) which belongs to the genus Banyangvirus in the family of Phenuiviridae. In vitro and in vivo studies of GTV demonstrated that it was able to infect animal and human cell lines and could cause pathological lesions in mice. Glycoproteins (GP, including Gn and Gc) on the surface of Guertu virus (GTV) could bind to receptors on host cells and induce protective immunity in the host, but knowledge is now lacking on the information of B cell epitopes (BCEs) present on GTV-GP protein. The aim of this study was to identify all BCEs on Gn of the GTV DXM strain using rabbit pAbs against GTV-Gn. Seven fine BCEs and two antigenic peptides (APs) from nine reactive 16mer-peptides were identified, which are EGn1 (2PIICEGLTHS11), EGn2 (135CSQDSGT141), EGn3 (165IP EDVF170), EGn4 (169VFQEL K174), EGn5 (187IDGILFN193), EGn6 (223QTKWIQ228), EGn7 (237CHKDGIGPC245), AP-8 (299GVRVRPKCYGFSRMMA314) and AP-9 (355CASH FCSSAESGKKNT370), of which six of mapped BCEs were recognized by the IgG-positive sheep serum obtained from sheep GTV-infected naturally. Multiple sequence alignments (MSA) based on each mapped BCE motif identified that the most of identified BCEs and APs are highly conserved among 10 SFTSV strains from different countries and lineages that share relatively close evolutionary relationships with GTV. The fine epitope mapping of the GTV-Gn would provide basic data with which to explore the GTV-Gn antigen structure and pathogenic mechanisms, and it could lay the foundation for the design and development of a GTV multi-epitope peptide vaccine and detection antigen.

Fine mapping epitope on glycoprotein Gc from Crimean-Congo hemorrhagic fever virus.

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne zoonosis, caused by CCHF virus (CCHFV) and which there are no diagnostic or therapeutic strategies. The C-terminus of glycoprotein (Gc) encoded by the CCHFV M gene is responsible for CCHFV binding to cellular receptors and acts as a neutralizing-antibody target. In this study, a modified biosynthetic peptide technique (BSP) was used to identify fine epitopes of Gc from the CCHFV YL04057 strain using rabbit antiserum against CCHFV-Gc. Six B cell epitopes (BCEs) and one antigenic peptide (AP) were identified: E1 (88VEDASES94), E2 (117GDRQVEE123), E3 (241EIVTLH246), AP-4 (281DFQVYHVGNLLRGDKV296), E5a (370GDTP QLDL377), E5b (373PQLDLKAR380), and E6 (443HVRSSD448). Western blotting analysis showed that each epitope interacted with the positive serum of sheep that had been naturally infected with CCHFV, and the results were consistent with that of Dot-ELISA. The multiple sequence alignment (MSA) revealed high conservation of the identified epitopes among ten CCHFV strains from different areas, except for epitopes AP-4 and E6. Furthermore, three-dimensional structural modeling showed that all identified epitopes were located on the surface of the Gc "head" domain. These mapped epitopes of the CCHFV Gc would provide a basis for further increase our understanding CCHFV glycoprotein function and the development of a CCHFV epitope-based diagnostics vaccine and detection antigen.

A novel tick-borne phlebovirus, closely related to severe fever with thrombocytopenia syndrome virus and Heartland virus, is a potential pathogen.

Tick-borne viral diseases have attracted much attention in recent years because of their increasing incidence and threat to human health. Severe fever with thrombocytopenia syndrome phlebovirus (SFTSV) and Heartland virus (HRTV) were recently identified as tick-borne phleboviruses (TBPVs) in Asia and the United States, respectively, and are associated with severe human diseases with similar clinical manifestations. In this study, we report the first identification and isolation of a novel TBPV named Guertu virus (GTV) from Dermacentor nuttalli ticks in Xinjiang Province, China, where TBPVs had not been previously discovered. Genome sequence and phylogenetic analyses showed that GTV is closely related to SFTSV and HRTV and was classified as a member of the genus Phlebovirus, family Phenuiviridae, order Bunyavirales. In vitro and in vivo investigations of the properties of GTV demonstrated that it was able to infect animal and human cell lines and can suppress type I interferon signaling, similar to SFTSV, that GTV nucleoprotein (NP) can rescue SFTSV replication by replacing SFTSV NP, and that GTV infection can cause pathological lesions in mice. Moreover, a serological survey identified antibodies against GTV from serum samples of individuals living in Guertu County, three of which contained neutralizing antibodies, suggesting that GTV can infect humans. Our findings suggested that this virus is a potential pathogen that poses a threat to animals and humans. Further studies and surveillance of GTV are recommended to be carried out in Xinjiang Province as well as in other locations.