Total RNA was extracted from 140 mL of each sample using the QIAamp viral RNA mini Kit (Qiagen, 52904) according to the manufacturer's instructions. RNA was eluted from the columns with 50 mL of diethyl pyrocarbonate (DEPC)-treated water containing 1 U DNaseI. Samples were incubated at 37uC for 15 minutes to eliminate human DNA, followed by DNase inactivation at 95uC for 10 minutes. RNA was used immediately or stored at 280uC. 