This study was conducted to investigate the effects of quercetin on the expression of cyclin-dependent kinase (CDK4) mRNA and protein in A549 lung epithelial tumor cells infected by H1N1. First, the Thiazolyl Blue Tetrazolium Bromide (MTT) method was used to determine H1N1 virulence, quercetin cytotoxicity and inhibition of the cytopathic effect of H1N1 on A549 cells by quercetin. Subsequently, 100 TCID50 H1N1 was used to infect A549 cells for 2 h prior to culture in maintenance media containing 10 mg/l quercetin. After 4, 12, 24 and 48 h of culture, the cells were collected and total RNA and protein were extracted. Fluorescent quantitative polymerase chain reaction and western blot analysis were then performed to assess the expression of CDK4 mRNA and protein. The experiment demonstrated that the TCID50 of H1N1 in A549 cells was 10(-4.75), the maximum non-toxic concentration of quercetin in A549 cells was 30-60 mg/l and the minimum effective concentration of quercetin for the inhibition of the H1N1 cytopathic effect on A549 cells was 10 mg/l. The results indicated that quercetin may significantly inhibit CDK4 mRNA and protein overexpression caused by H1N1 within 4-48 h. In conclusion, quercetin may protect against H1N1 infection by effectively reducing the mRNA and protein expression of CDK4 caused by H1N1 infection.
