Rabbit antiserum to 16L1/L2-16E7 VLPs neutralizes in vitro generated pseudotype HPV16 virions. HPV16L1/L2 recombinant SFV stock was used to infect BPHE-1 cells harboring the BPV1 genome (29). Cell lysates containing the resulting pseudotype HPV16 virions were incubated with preimmune at a dilution of 1:50 (A) or immune serum to HPV16 L1/L2 VLPs at dilutions of 1:10,000 (B) or 1:30,000 (C), or preimmune at a dilution of 1:50 (D) or immune serum to HPV16 L1/L2-16E7 VLPs at dilutions of 1:10,000 (E) or 1:30,000 (F), and placed onto monolayers of C127 cells. After 3 weeks, the cells were stained with 0.5% (wt/vol) methylene blue/0.25% (wt/vol) carbol fuschin in methanol, and the number of foci was scored (45).