S. PFAENDER¹, E. GRABSKI², C. DETJE², N. RIEBESEHL¹, S. LIENENKLAUS³, E. STEINMANN¹, U. KALINKE², T. PIETSCHMANN<sup>1

1</sup>Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research, Hannover, Germany, ²Institute for Experimental Infection Research, TWINCORE, Centre for Experimental and Clinical Infection Research, Hannover, Germany, ³Department of Molecular Immunology, Helmholtz Centre for Infection Research, Braunschweig, Germany

Hepatitis C virus (HCV) strongly induces interferon (IFN) stimulated genes in the infected liver despite of distinct innate immune evasion mechanisms. Recent studies indicate that a rare subset of myeloid dendritic cells (CD141+ DC) produces type III IFN upon stimulation with cell-culture derived HCV whereas plasmacytoid dendritic cells (pDC) are able to produce large amounts of type I IFN. To improve our understanding of the interplay between HCV and dendritic cells, we aimed at dissecting the requirements for DC stimulation by using mouse-derived DC and mouse genetics. Using murine bone marrow-derived in vitro differentiated DC cultures we observed an IFN response upon coculture with HCV RNA transfected human or murine hepatoma cells. Both full length and subgenomic HCV replicons triggered IFN-release by murine DC. Injection of human HCV subgenomic replicon cells into type I interferon reporter mice confirmed the interferon induction upon HCV replication in vivo. Moreover, transfer of conditioned culture fluid from HCV-replicating cells activated DC and elicited IFN release indicating a cell-cell contact independent stimulation of the DC. Using differentiated DC from mice with distinct genetic lesions in innate immune signalling we observed that IFN secretion by HCV-stimulated murine DC was independent of MyD88 and CARDIF, but dependent on TRIF and IFNAR signalling. Separating mouse DC cultures into pDC and conventional CD11b-like cDC and CD8α-like cDC revealed that the CD8α-like cDC, which are homologous to the human CD141+ DC, release interferon upon stimulation by HCV replicating cells. In contrast, the other cell types did not. Collectively, these results indicate that HCV-replicating cells stimulate IFN secretion from murine CD8α-like cDC. This model should be useful to explore the interaction between dendritic cells during HCV replication and to define how viral signatures are delivered to immune cells to trigger IFN release.