Project Summary/Abstract Biliary atresia is the most common cause of pediatric end stage liver disease and the number one indication for pediatric liver transplantation. Because pathogenic viruses have been found in the liver of afflicted children, a proposed etiology for biliary atresia is a perinatal viral infection triggering immune mediated destruction of the biliary epithelium. The murine model of biliary atresia supports a viral pathogenesis as newborn mice infected with rhesus rotavirus (RRV) develop inflammation within the portal tract and extrahepatic bile duct obstruction. RRV targets the cholangiocyte for infection and in addition to direct cholangiocyte injury also induces Natural Killer cell mediated injury to the biliary epithelium. We have previously shown that the amino acid, arginine (R) within the sequence “SRL” (amino acids 445-447) on the RRV VP4 protein is required for viral binding and entry into biliary epithelial cells. We developed a reverse genetics system to create a mutant of RRV (RRVVP4-R446G), which had a single amino acid change in VP4 protein compared to wild type RRV. In vitro, the mutant virus had reduced binding and infectivity in cholangiocytes. In vivo, it produced less symptoms and mortality in neonatal mice, resulting in an attenuated form of biliary atresia. We will use this mutant strain along with additional VP4 mutants to determine how RRV binds to, enters, traffics through the cell, and ultimately activates the cholangiocyte's innate immune response. We will also ascertain these VP4 mutants' ability to infect and activate plasmacytoid dendritic cells leading to Natural Killer cell activation. These complimentary approaches will generate new insight in viral induced biliary atresia.