The coding sequence of RSV G protein from RSV A2 strain was amplified from cDNA by PCR and cloned into the EcoR I and Xho I sites of pFastBac-1 vector (Fig. 1A) . The recombi-nant baculovirus was subsequently generated by using the Bac-to-Bac Ⓡ system (Invitrogen) following the manufacturer's instructions. The recombinant baculoviruses were purified from supernatants of infected Sf9 insect cells with 25% (w/v) sucrose in 5 mM NaCl, 10 mM EDTA in a SW28 rotor (Beckman, USA) at 24,000 rpm for 75 min at 4 o C. The supernatant was decanted, and the pellet was resuspended in phosphate-buffered saline (PBS) and centrifuged for 4 h at 24,000 rpm, 4 o C. The viral pellet was resuspended in PBS and titrated by plaque assays on Sf9 cells.