Detection of HCV RNA in cultured cells by in situ hybridization with S35-labeled RNA probes and detection of HCV protein by fluorescence microscopy. (A, B) Infected B-cells hybridized with labeled positive-strand RNA probe. (C) Freshly transformed uninfected B-cells showing no significant hybridization. (D) Picture of freshly transformed uninfected B-cells showing no significant hybridization and having a wider field of view than (C). (E) Infected B-cells hybridized with labeled negative-strand RNA probe. (F) HCV infected cells: PCLBT4 treated with human polyclonal IgG purified from the serum of patient 081 and stained with goat anti-human IgG conjugated with fluorescein isothiocyanate (FITC). PCLBT4 is the fourth consecutive transfer of HCV to freshly immortalized B-cells.