To further elucidate the molecular mechanisms by which PRRSV inhibits the induction of interferon- transcription in MARC-145 cells, Luo et al. examined the role of several key molecules in mediating the transcriptional activation of interferon- [26] . They reported that PRRSV interferes with the nuclear translocalization of IRF-3 by inactivating IPS-1, a downstream molecule of the RIG-I pathway [26] . Studies by Beura et al., suggested that the nonstructural proteins of PRRSV, including Nsp1, Nsp2, Nsp11 and Nsp4, when over-expressed in cell culture alone have the ability to antagonize the nuclear translocation of IRF-3 and the promoter activity of interferon- activated by Poly I:C and Sendai virus [27] . Similar studies have to some degree confirmed that over-expressed Nsp1 and Nsp2 of PRRSV in cell culture antagonize the promoter activity of interferon- as determined by using the luciferase reporter gene expression system [15, 28, 29, 30] . Sun et al. provided a detailed review on the role of PRRSV nonstructural and structural proteins in modulating the transcriptional activation of type I interferon in MARC-145 cells and human cell culture system including HeLa cells and 293T cells [12] . Despite the ease and convenience of using the luciferase reporter system to dissect the role of over-expressed viral proteins in regulating the transcription of interferon-, such results are often contradictory to the authentic virus infection of natural susceptible cells in vitro and in vivo [10, 16, 31] . Therefore, the implication of such results in natural virus infection is uncertain.