Three panels showing HCV replication and protein expression in IFN resistant replicon cell lines. (A) Shows growth of nine different HCV replicon cell lines in medium containing 1 mg/ml G-418 in the presence of IFN-α2b. All cell lines grew and formed IFN-resistant cell colonies. Cyclosporin-A (1 mg/ml) inhibited the colony formation in the replicon cell lines in presence of G-418. (B) HCV replication is resistant to IFN-α2b treatment in nine different replicon cell lines. Stable cell lines were treated with or without IFN-α2b (1000 IU/ml) and cyclosporine-A (1 mg/ml) for a week. Intracellular HCV positive strand RNA was measured by RPA using an antisense riboprobe targeted to the 5'UTR. (C) Shows the effect of IFN-α2b on NS3 protein expression in interferon sensitive versus interferon resistant cell clones. Replicon cells in chamber slides were treated with IFN-α2b (1000 IU/ml) for a week, and immunostaining for NS3 protein was performed using a monoclonal antibody. IFN treatment abolished NS3 protein expression in sensitive cells (S-5/15). No inhibition was seen in any of these three resistant cell lines (R-Con-15, R-Con-17 and R-Con-24).