Kinetics of antiviral gene expression in foot-and-mouth disease virus serotype O infected BHK-21 cells.

Release of type I interferon (IFN) is the immediate response of a cell to a viral infection. Even though BHK-21 cell is being used for the large-scale vaccine production of various viruses, its IFN response upon viral infection is not known hitherto. The BHK-21 cell innate antiviral response to foot-and-mouth disease virus (FMDV) will be useful in maximizing the virus titer by knocking out the dominant antiviral gene(s) from BHK-21 cells. Accordingly, we determined the relative mRNA expression of antiviral genes upon FMDV serotype O infection in BHK-21 cells. The relative fold change in the expression of type I IFN and interferon-stimulated genes (ISGs) such as IRF-3, IRF-7, ISG15, Mx1, and viperin transcripts were analysed at 2 h intervals till 8 h post-infection (hpi) by quantitative real-time reverse transcription PCR (RT-qPCR). The FMDV infection downregulated the relative expression of type I IFN at all the time points tested except at 2 hpi, where it had a transient up-regulatory effect. In contrast, the ISGs such as Mx1, ISG15, and IRF-7 showed a modest upregulation from 4 hpi onwards. Weak upregulation of IFN transcripts might be the reason behind the inherently higher titer of FMDV in the BHK-21 cells and deleting ISG(s) from the BHK-21 cells may further increase the FMDV titer.