PFAENDER¹, S. WALTER¹, D. TODT¹, E. GRABSKI², T. GATHER³, S. MÖLLER³, R.J.P. BROWN¹, A. POSTEL⁴, K. HAHN⁵, C. PUFF⁵, V. PFANKUCHE⁵, F. HANSMANN⁵, P. BECHER⁴, U. KALINKE², W. BAUMGÄRTNER⁵, K. FEIGE³, T. PIETSCHMANN¹, J-M.V. CAVALLERI³, E.STEINMANN¹

¹Institute for 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, ³Clinic for Horses, University of Veterinary Medicine Hannover, Bünteweg 9, 30559 Hannover, ⁴Institute of Virology, University of Veterinary Medicine Hannover, ⁵Department of Pathology, University of Veterinary Medicine Hannover, Bünteweg 17, 30559 Hannover

Hepatitis C virus (HCV) has a restricted host species tropism, naturally infecting only humans, although chimpanzees are susceptible to experimental infection. A robust immunocompetent animal model is still lacking, hampering mechanistic analysis of virus pathogenesis, immune control and prophylactic vaccine development. The closest homolog of HCV discovered to date is the nonprimate hepacivirus (NPHV) which shares similar features with HCV and thus could represent a useful model to study hepacivirus infections in their natural hosts. In this study, we aimed to dissect equine immune responses after experimental NPHV infection. In addition, we conducted challenge experiments to investigate immune protection against secondary NPHV infections. To this end, three horses were intravenously injected with NPHV containing plasma. Fluorescent activated cell sorting (FACS)-based assays were established to monitor immune cell frequencies and activation status. Cytokines were measured on mRNA level by the development of quantitative real-time polymerase chain reactions and on protein level by a bead-based multiplex assay. To study whether infected horses are protected against a secondary infection, horses were re-challenged with the same as well as with a distinct NPHV inoculum. All infected horses became viremic after one or two weeks and viremia could be detected for several weeks followed by a delayed seroconversion and viral clearance. Histopathological examinations were conducted revealing moderate, periportal infiltrations of lymphocytes with some horses displaying signs of hepatitis. Immune responses differed between all horses; however, no distinct immune pattern could be observed. Importantly, after a primary NPHV infection horses were protected against re-challenge with the identical as well as a distinct isolate. In conclusion, horses were successfully infected with NPHV containing plasma. Techniques were established to monitor the underlying immune responses and to dissect mechanisms contributing to viral clearance and immune protection. Detailed understanding of hepacivirus infections in their natural hosts could facilitate the development of new therapeutic strategies including protective vaccines against HCV.