Interferon-stimulated genes. RNA samples of Caco-2 cells (A) and HEK 293 cells (B) described in Fig. 2 were investigated by RT-PCR for the presence of ISG56 and MxA mRNAs. As for IFN-α (see Fig. 2A), for detection of MxA mRNA in Caco-2 cells an extended infection period of 24 h was necessary (A, lower right panel).