FIG. 7.

In vivo-produced 2a_ΔHVR1 virus displayed greatly increased neutralization susceptibility resembling that of in vitro-produced 2a_ΔHVR1 virus. In vivo-produced viruses used were without dominant envelope mutations; 2a virus was from mouse B156 serum, and 2a_ΔHVR1 virus was from mouse B150R plasma. A virus dose of 10 TCID₅₀s/well was used. Mouse-derived 2a and 2a_ΔHVR1 viruses were incubated in 24 replicates for 1 h at 37°C with either medium or a dilution of SA3 serum prior to infection of Huh7.5 cells. The number of FFUs/well was visualized following 48 h of infection by HCV-specific immunostaining. The number of FFUs/well was normalized to the virus-only infection without serum and is shown with the SEM. The asterisk for 2a_ΔHVR1 virus and SA3 serum diluted 1:200 indicates that no infected cells were observed. Values that were significantly different (P < 0.0001) are indicated by a bar and three asterisks. Values that were not significantly different at a significance level of P = 0.05 are indicated by a bar and ns. (A) In vivo-produced 2a and 2a_ΔHVR1 viruses subjected to neutralization with a 1:200 dilution of SA3 serum showed no neutralization of 2a and complete neutralization of 2a_ΔHVR1 as observed for in vitro-produced viruses (Table 3). (B and C) In vivo- and in vitro-produced 2a_ΔHVR1 subjected to neutralization with a 1:4,000 dilution of SA3 serum displayed statistically significant and similar neutralization of about 70 to 80%, whereas the original 2a viruses produced in vivo and in vitro were not neutralized.