2.11. Splenocyte proliferation assay
Spleen cells (2×106 cells) from the immunized mice were seeded in the tissue culture plates (Corning, USA) and stimulated with ORF8 (10 μg/mL) at 37 °C with 5% (v/v) CO2 for 60 h. Cells were stimulated with 1 μg ConA/mL, which served as a positive control. Cells were stimulated with medium alone, which acted as a negative control. Proliferation was determined by CCK-8 vital stain (Dojindo Laboratories, USA). The proliferation index (PI) was calculated as the ratio of the average OD450 value of the ORF8-stimulated cells to the one of the medium-stimulated cells.