African Swine Fever Virus H240R Protein Inhibits the Production of Type I Interferon through Disrupting the Oligomerization of STING

African swine fever (ASF) is a highly contagious and acute hemorrhagic viral disease in domestic pigs and wild boars. Domestic pigs infected with virulent African swine fever virus (ASFV) isolates have a high mortality, approaching 100%. Identification of ASFV genes related to virulence/pathogenicity and deletion of them are considered to be key steps in the development of live attenuated vaccines, because the ability of ASFV to escape host innate immune responses is related to viral pathogenicity. However, the relationship between the host antiviral innate immune responses and the pathogenic genes of ASFV has not been fully understood. In this study, the ASFV H240R protein (pH240R), a capsid protein of ASFV, was found to inhibit type I interferon (IFN) production. Mechanistically, pH240R interacted with the N-terminal transmembrane domain of stimulator of interferon genes (STING) and inhibited its oligomerization and translocation from the endoplasmic reticulum to the Golgi apparatus. Additionally, pH240R inhibited the phosphorylation of interferon regulatory factor 3 (IRF3) and TANK binding kinase 1 (TBK1), leading to reduced production of type I IFN. Consistent with these results, infection with H240R-deficient ASFV (ASFV-ΔH240R) induced more type I IFN than infection with its parental strain, ASFV HLJ/18. We also found that pH240R may enhance viral replication via inhibition of type I IFN production and the antiviral effect of interferon alpha (IFN-α). Taken together, our findings provide a new explanation for the reduction of ASFV's replication ability by knockout of the H240R gene and a clue for the development of live attenuated ASFV vaccines. IMPORTANCE African swine fever (ASF), caused by African swine fever virus (ASFV), is a highly contagious and acute hemorrhagic viral disease with a high mortality, approaching 100% in domestic pigs. However, the relationship between viral pathogenicity and immune evasion of ASFV is not fully understood, which limits the development of safe and effective ASF vaccines, specifically, live attenuated vaccines. In this study, we found that pH240R, as a potent antagonist, inhibited type I IFN production by targeting STING and inhibiting its oligomerization and translocation from the endoplasmic reticulum to the Golgi apparatus. Furthermore, we also found that deletion of the H240R gene reduced viral pathogenicity by enhancing type I IFN production, which decreases ASFV replication. Taken together, our findings provide a clue for the development of an ASFV live attenuated vaccine via deleting the H240R gene.