Vero cells

Vero cells were obtained from the Korean Cell Line Bank (Product #10081, Seoul, Korea) and MRC-5 cells from the American Type Culture Collection (Product #CCL-171, ATCC, Manassas, VA, USA). Vero cells and MRC-5 cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM, ATCC) and Eagle’s Minimum Essential Medium (EMEM, ATCC), respectively, with 10% fetal bovine serum (FBS, Thermo Fisher Scientific, Waltham, Massachusetts, USA), penicillin (100 U/mL), and streptomycin (100 µg/mL). Cells were maintained in 95% air and 5% CO₂ at 37 °C.

Monkey kidney fibroblasts (Vero cells) were purchased from the Korean Cell Line Bank. Vero cells were cultured in RPMI-1640 medium, supplemented with 10% fetal bovine serum, 1% streptomycin (100 μg/mL), and penicillin (100 unit/mL⁻¹) and maintained at 37 °C in a 5% CO₂ incubator [26 (link)].

Vero cells (African green monkey kidney cells) were purchased from the Korean Cell Line Bank (KCLB, Seoul, Republic of Korea). Cells were incubated at 37 °C with 5% CO₂ in RPMI 1640 containing 10% fetal bovine serum (FBS), penicillin (10,000 Units/mL), and streptomycin (10 mg/mL). Cells were subcultured or seeded upon reaching 80–90% confluency for experiments.

Vero cells and Vero E6 cells, the African green monkey kidney cells, and Calu-3 cells, the human airway epithelial cells were purchased from the Korean Cell Line Bank (Seoul, Korea). The cells were cultured in Dulbecco's modified Eagle's medium (DMEM, Thermo Fisher Scientific, Waltham, MA, USA) containing 10% fetal bovine serum (FBS, Thermo Fisher Scientific), 25 mM HEPES, 100 U/ml penicillin, and 100 μg/ml streptomycin in 95% atmospheric air and 5% CO₂ at 37˚C. MERS-CoV/KOR/KNIH/002_05_2015 was obtained from the Korea Centers for Disease Control and Prevention (Permission No. 1-001-MER-IS-2015001). SARS-CoV-2 (NCCP No. 43326) was provided by the National Culture Collection for Pathogens (Osong, Korea). MERS-CoV and SARS-CoV-2 preparation and cell culture procedures were performed in biosafety level-3 conditions.

Vero cells (Korean Cell Line Bank, KCLB No. 10081, Korea) were cultured in Dulbecco’s modified Eagle’s medium (DMEM), supplemented with 10% FBS, 50 U/ml penicillin, and 50 μg/ml streptomycin. SARS-CoV-2 isolates (NCCP no. 43326 for the S clade, NCCP no. 43390 for the GK clade [B.1.617.2 lineage, Delta], and NCCP no. 43408 for the GRA clade [B.1.1.529, Omicron]) were provided by the National Culture Collection for Pathogens. The wild-type virus or variants were propagated in Vero cells with DMEM + 2% FBS. At 72 h after infection, culture supernatants were collected and stored at −80 °C. Viral titer was determined by focus formation assay as described previously with slight modifications^{10 (link)}. Ten-fold serial dilutions of wild-type virus or variants were incubated with the Vero cells for 1 h before further overlaying of 2% methyl cellulose in 4% FBS in DMEM. Subsequent procedures were conducted under the identical condition as described in Section of Focus reduction assay. Virus titers were calculated as focus forming units (FFU) per ml. All experiments with SARS-CoV-2 were conducted in a Biosafety Level 3 laboratory.

Vero cells (Korea Cell Line Bank, Seoul, Korea) were transfected with 5 μg of mRNA-Gn using Lipofectamine 2000® (Invitrogen, Waltham, MA, USA). After 24 h, cell lysates were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and transferred onto a nitrocellulose membrane. Membranes were blocked with phosphate-buffered saline (PBS) containing 0.1% Tween-20 and 5% skim milk for 1 h at room temperature. The membrane was then incubated overnight at 4 °C with an anti-SFTSV Gn antibody (1:1000 dilution, NBP2-41156; Novus Biological, Centennial, CO, USA) and anti-beta actin antibody (1:3000 dilution, 3700 S; Cell Signaling Technology, Danvers, MA, USA). The secondary antibodies used were anti-rabbit or anti-mouse antibodies conjugated with horseradish peroxidase (1:5000 dilution; A120-101P or A90-116P; BETHYL, Montgomery, TX, USA). Signals were detected using an ECL substrate solution (ECL-PS100; Donginbio, Seoul, Korea). The uncropped western blot images are shown in Supplementary Fig. 1.