Cathepsin B treatment of HPV16 increases infection. HPV16 DsRed reporter-virions were incubated with (A) 37 pM cathepsin B protease or (B) 37 pM cathepsin L protease for various amounts of time. 293 cells were infected with protease treated reporter-virions or infected with untreated reporter-virions (control). Infections were analyzed by flow cytometry for DsRed expression 48 hours post binding. 293 cells alone were used as control for background fluorescence. Statistics were analyzed by 1 tailed t-test and found be significant at P < 0.05.