Mrc 5 human lung fibroblast host cells

For virus culture, HCoV-229E was purchased from the American Type Culture Collection (ATCC, Manassas, VA, USA) while MRC-5 human lung fibroblast host cells were purchased from the Korean Cell Line Bank (KCLB, Seoul, Korea). The QuantiChrom Nitric Oxide Assay Kit and QuantiChrom Peroxide Assay Kit (BioAssay Systems, Hayward, CA, USA) were used to measuring total NO and H₂O₂ levels, respectively, and the alamarBlue Assay Kit (Invitrogen, Waltham, MA, USA) was used to measure cell cytotoxicity. All procedures were performed according to the manufacturers' instructions. Chloroquine diphosphate and ritonavir were purchased from Sigma-Aldrich (Yongin, Korea). Stocks of these drugs were prepared in dimethyl sulfoxide (DMSO) and stored at −20 °C until further use. An antibody specific to the HCoV S protein was obtained from Sino Biological (Chesterbrook, PA, USA). All cell culture plasticware was purchased from SPL Life Sciences (Pocheon, Korea). Nitrogen (99.99%) and oxygen (99.99%) gases were purchased from Dong-A Scientific (Seoul, Korea). Other analytical reagent-grade solvents and chemicals were purchased from Sigma-Aldrich (Merck, St. Louis, MO, USA). Distilled water with a resistivity of 18.2 MΩ.Cm, obtained from a Milli-Q® water purification system (Millipore, Bedford, MA, USA) was used to prepare all aqueous solutions in this study.