GSE158753
Pathogenesis, miR-122 gene-regulation, and protective immune responses after acute infection of horses with equine hepacivirus
Equine hepacivirus (EqHV) is the closest genetic relative of hepatitis C virus (HCV) and shares features of genome organization, hepatotropism, persistent infection, and the ability to cause liver disease. As such, EqHV studies are important both in order to understand equine liver disease, and as an outbred animal model for HCV pathogenesis and immune responses. Here, we characterize the natural history and immune response to EqHV infection. Seven horses were experimentally inoculated with EqHV, monitored for 6 months, and challenge inoculated with the same, and subsequently a divergent EqHV inoculum. Clearance was the primary outcome (6 of 7) and was associated with subclinical hepatitis characterized by lymphocytic infiltrate and individual hepatocyte necrosis. Seroconversion was delayed and antibody titers waned slowly. Resolving horses developed non-sterilizing immunity resulting in short duration of infection upon challenge. Unlike those observed in acutely HCV-infected patients, peripheral blood mononuclear cell responses in horses were minimal, although EqHV specific T-cells were identified. In contrast, an interferon stimulated gene signature was detected in the liver during EqHV infection, which is similar to acute HCV in humans. EqHV, similarly to HCV, is stimulated by direct binding of the liver-specific microRNA, miR-122. Surprisingly, we found that EqHV infection sequesters enough miR-122 to functionally affect gene regulation in the liver. This RNA-based mechanism thus could have consequences for pathology. Conclusion: EqHV infection in horses typically has an acute resolving course, and the immune response attenuates subsequent infections lasting for at least a year. This could have important implications to achieve the first goal of an HCV vaccine; to prevent chronicity while accepting acute resolving infection after challenge. Overall design: Seven horses were experimentally infected with equine hepacivirus (EqHV). RNA-Seq on PBMC and liver biopsies was performed pre-inoculation (PRE), during early acute infection (ACUTE), near seroconversion (SC), during falling viremia (FV), and at week 26 (POST). Six horses cleared the infection within the 26 weeks, and these were challenged with homologous serum (week 26) and heterologous serum (week 30-32). Additional challenge time points were included for horses that became positive during challenge and where sampling was possible (horses A, P, R for liver, horses A, N, P, R for PBMCs). One replicate was processed per horse per time point. PBMC libraries were poly-A selected; liver biopsy libraries were total RNA-seq (ribo-depletion).