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

To assess whether the upregulation of these cytokines and chemokines was IFN dependent, we analyzed only BMM, since BMDC produced very low levels of these molecules and did not express type I IFN. We also included an additional IFNresponsive gene ISG15 (IFN-stimulated gene 15) in these assays. Consistent with a previous study of lipopolysaccharide (LPS)-treated BMM and BMDC (41), we found that CXCL10, IL-10, and ISG15 expression was dependent on IFNAR, but not MyD88, signaling (Fig. 5) . TNF, IL-6, and IL-12 p40 mRNA upregulation was abolished in MHV-infected MyD88 Ϫ/Ϫ cells and was variably dependent upon IFNAR signaling: the levels of IL-6 and IL-12 p40 were decreased by about 50 to 80% in IFNAR Ϫ/Ϫ BMM ( Fig. 5A and B) . These mRNA data were confirmed by measuring the levels of CXCL10, TNF, and IL-12 p70 protein in an ELISA (Fig. 5C ). As in MHV-infected cells, CXCL10 expression in SenV-infected or poly(I · C)-transfected BMM was also dependent on IFNAR, but not MyD88. However, TNF expression in these samples was not dependent on MyD88, consistent with a previous report showing that TNF expression was mediated by direct MDA5 recognition in SenV-infected cells (Fig. 5A) (42) . IL-6 and IL-12 p40 were expressed at very low levels in poly(I · C)-treated or SenV-infected BMM, so expression of these cytokines was not analyzed further.