FIG. 3.

Cell specificity of the IFN-λ response is receptor mediated and independent of a functional IFN-α receptor. (A and B) Different cell lines were stimulated with 0.02 μg/ml IFN-α (A) or 0.05 μg/ml IFN-λ (B), and the expression levels of ISG56/IFIT1, OAS1, IFITM1/9-27 h, and Viperin/cig5 were estimated by real-time PCR. Cell lines used were HepG2, MCF-7, MDA-MB-231, and SW13. All values were normalized to the GAPDH expression level, and for cells not stimulated by IFN, the expression level was normalized to 1. (C) Expression ratio of IL28Rα and IL10Rβ. The expression levels of the IFN-λ receptor subunits IL28Rα and IL10Rβ were estimated by real-time PCR in Raji, HepG2, MCF-7, MDA-MB-231, SW13, and HT1080 cells. Values were normalized to the corresponding GAPDH values. Data are presented as the expression ratio between IL28Rα and IL10Rβ. Note that IL10Rβ was expressed in a relative constant ratio to GAPDH in the examined cell lines. (D) Expression of the IFN-λ receptor IL28Rα subunit restores IFN-λ signaling, and IFN-λ signaling functions independent of the IFN-α receptor. HT1080 cells and HT1080-U5A cells were used in the analysis with the latter lacking a functional IFNAR2 receptor subunit. Cells were stimulated with 0.1 μg/ml IFN-λ or 1 kU/ml IFN-α. U5A/IL28Rα indicates that cells were transiently transfected with an expression vector for IL28Rα. Using real-time PCR, the expression level of ISG56 was determined and normalized to the GAPDH expression level and given the value 1 for the expression level in cells not stimulated by IFN.