Fig. 2.

CTSL is elevated in SARS-CoV-2 pseudovirus-infected cells in vitro. a Schematic of the validation assay setup. Huh7 cells were infected with different doses of SARS-CoV-2 pseudovirus (from 0.047 × 10⁴ TCID₅₀/ml to 1.30 × 10⁴ TCID₅₀/ml). Cells not infected with pseudovirus were used as controls. Luciferase activity and VSV-P mRNA levels were measured to evaluate infection severity. The mRNA and protein levels of CTSL and CTSB in Huh7 cells were measured to validate the clinical data. b, c Luciferase activity (n = 4) (b) and VSV-P mRNA (n = 8) (c) levels increased dose-dependently 24 h after pseudovirus infection. Statistical significance was assessed by Brown–Forsythe and Welch’s ANOVA with Dunnett’s post hoc test in b by with the Kruskal–Wallis test with Dunn’s post hoc test for c. d, e Effects of SARS-CoV-2 pseudovirus infection on CTSL and CTSB mRNA levels (d) and protein levels (e). n = 6. Statistical significance was assessed by the Kruskal–Wallis test with Dunn’s post hoc test. Data are expressed as the mean ± s.e.m. values. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001