P113 Evasion of interferon type I induction by African swine fever virus

Introduction African swine fever virus (ASFV) is characterised by its ability to interfere with signalling pathways controlling the transcription of cytokines. Curiously, the modulation of the interferon response by ASFV has only been described in the comparison of transcriptional profiles of macrophage cells infected with wild type virus and a deletion mutant virus lacking six MGF360 and two MGF530 genes. However, precisely which gene(s) within the multigene families are responsible for this activity and its mechanism of action remain unknown. Methods Hence, in this study, these and several other genes of ASFV with unassigned functions were tested for their ability to inhibit the expression of IFN- β using luciferase reporter gene assays. Vero cells were transfected with the ASFV genes together with a IFN- β luciferase reporter plasmid and were either stimulated or not stimulated with 25 μg/ml Poly (I:C) for five hours. Ectopic overexpression of signalling intermediates as also used in this luciferase reporter assays to determine at which level were the viral genes inhibiting the IFN- β signalling pathway. The phosphorylation and translocation of the critical transcription factors, IRF-3 and IRF-7, were analysed by western blot and immunofluorescence. Results Interestingly, the A276R gene belonging to the multigene family 360, was shown to impair the induction of IFN- β via an NF- κ B independent mechanism. To further characterise the modulation of the type I IFN response by A276R, the impact of ectopic expression of the key elements of both TLR and cytosolic pathways on A276R-mediated inhibition was done and the results suggest that IRF-3, a key regulator of type I IFN responses, is the target of A276R. Additionally, other unassigned gene, the K205R, was also identified as an inhibitor of IFN- β expression and the mechanism of the inhibition appears to be at the level of IRF-7. Conclusion This work presents two different mechanisms for the inhibition of IFN- β induction by two ASFV unassigned viral genes. In conclusion, the multiplicity of genes evolved by ASFV to subvert the IFN response emphasises the essential role of this system in innate anti-virus immunity.