RIGI and infection: Here we observed that although A/tree sparrow/Henan/1/04(H5N1) effectively infected human lung epithelial cells and induced rapid IFN-β production during early infection (0-4h) (Figure 1B), its infection only induces low level endogenous RIG-I expression compared with H1N1 in A549 cells based on western blot and RT-PCR and that they are in agreement (Figure 2).