FIG. 4.

Titration of the HPV-16-neutralizing activity in the anti (α)-HPV-16 VLP and the anti-HPV-33 VLP sera. HPV-16 stock diluted 1:10⁴ was preincubated with serial log₁₀ dilutions of anti-HPV-16 L1 VLP or anti-HPV-33 L1 VLP antiserum prior to addition to HaCaT cells. RT-PCR products obtained with HPV-16-specific primers are shown. Lanes are labeled with the reciprocal dilution of antiserum used in the experiment. Lane V represents RT-PCR product obtained with RNA isolated from cells infected with HPV-16 preincubated with a 1:100 dilution of normal serum. Lane C represents the RT-PCR product obtained with RNA from uninfected cells.