Autocrine Interferon Priming in Macrophages but Not Dendritic Cells Results in Enhanced Cytokine and Chemokine Production after Coronavirus Infection

Zhou, Haixia; Zhao, Jincun; Perlman, Stanley

IFN-␤ treatment upregulated expression of IFNAR-dependent molecules MDA5, RIG-I, CXCL10, and ISG15 in mock-infected BMM and BMDC to maximal levels as early as 4 h posttreatment, and the level remained constant over the next 8 hours (Fig. 6C and D) . In contrast, expression of these molecules was minimal in MHV-infected BMM at 8 h p.i. but increased over the following 12 to 16 h p.i. (Fig. 2B and C, 4A, and 6C and D) . Exogenous IFN-␤ treatment enhanced expression of these molecules compared to MHV infection alone at 8 but not 16 h p.i., again suggesting that the amount of IFN produced by infected BMM was sufficient for maximal expression at later times p.i. (Fig. 6C and D) . We detected much higher mRNA levels of MDA5 and RIG-I in MHVinfected BMM at 16 h p.i. than in IFN-␤-treated mock-infected cells, although the IFN level induced by MHV was actually lower than 800 U (Fig. 1A and B) . This likely occurred because MDA5 and RIG-I recognize viral PAMPs and directly upregulate expression of these IFN-dependent molecules via a positive-feedback loop. Additionally, these results also suggest that the effects of IFN on neighboring uninfected cells do not account for the elevated levels of IFN, MDA5, and RIG-I detected in these cultures after MHV infection, since the levels were substantially greater than those observed after IFN treatment of mock-infected cells.