Effect of Crataegus pinnatifida Fructus treatment on virus binding to cells. (a and b) The effect of Crataegus pinnatifida Fructus treatment on BKPyV (a) or JCPyV (b) binding to cells was visualized by fluorescence microscopy. (c and d) The inhibition of BKPyV (c) or JCPyV (d) binding to cells by Crataegus pinnatifida Fructus was analyzed by flow cytometry. Alexa Fluor 488-labeled BKPyV or JCPyV was preincubated with various concentrations of Crataegus pinnatifida Fructus extract for 1 h at 4°C. The mixtures were then added to prechilled cells and allowed to bind for another 1 h at 4°C. The cells were fixed and washed with ice-cold PBS before analysis by microscopy or flow cytometry. F-BKV, Alexa Fluor 488-labeled BKPyV; F-JCV, Alexa Fluor 488-labeled JCPyV; 50, 100, or 200 cra, Crataegus pinnatifida Fructus used at a concentration of 50, 100, or 200 μg/mL, respectively.