Fig. 1.

Immune human sera and IgG neutralize HPV-18 and show high efficacy in preventing infection of PHKs. (A) HPV-18 neutralization by four matched pairs of sera collected pre- and post-immunization with Gardasil. One example of pre-immune (4911) and immune (4921) sera is shown here. Additional data are presented in Table 2. PHKs at passage two were infected with HPV-18 at MOI 20 in the presence of diluted sera (1:300, 1:600, 1:1200, 1:2400 and 1:4800). Infection was detected by the presence of a cDNA fragment of a spliced E1^E4 mRNA via RT-nested PCR. β-actin cDNA served as a control. (B) IgG was responsible for the HPV-neutralizing activity in the serum. IgG was isolated from pre-immune (4911) and immune (4921) sera. PHKs were infected with HPV-18 at MOI 20 in the presence of purified IgG. IgG of 13.3, 6.6, 3.3, 1.6 and 0.8 μg corresponded to the serum serial dilutions in Fig. 1A. Uninfected PHKs and PHKs infected in the absence of serum were negative and positive infection controls, respectively (A & B, left two lanes). M, 50 bp DNA ladder.