Perforin and granzymes work in synergy to mediate cholangiocyte injury in experimental biliary atresia

Background & Aims Biliary atresia represents obstructive cholangiopathy in infants progressing rapidly to cirrhosis and end-stage liver disease. Activated NK cells expressing Nkg2d have been linked to bile duct injury and obstruction by establishing contact with cholangiocytes. To define the mechanisms used by cytotoxic cells, we investigated the role of perforin and granzymes in a neonatal mouse model of rotavirus (RRV)-induced biliary atresia. Methods We used complementary cell lysis assays, flow cytometric analyses, quantitative PCRs and in vivo systems to determine the mechanisms of bile duct epithelial injury and the control of the tissue phenotype in experimental biliary atresia. Results RRV-infected hepatic NK and CD8 T cells increased the expression of perforin and injured cholangiocytes in short-term culture in a perforin-dependent fashion. However, the loss of perforin in vivo delayed but did not prevent the obstruction of bile ducts. Based on the increased expression of granzymes by perforin-deficient cytotoxic cells in long-term cytolytic assays, we found that the inhibition of granzymes by nafamostat mesilate (FUT-175) blocked cholangiocyte lysis. Administration of FUT-175 to perforin-deficient mice after RRV infection decreased the development of jaundice, minimized epithelial injury, and improved long-term survival. However, the inhibition of granzymes alone in wild-type mice was not sufficient to prevent the atresia phenotype in newborn mice. In infants with biliary atresia, hepatic Granzymes A and B mRNA, but not Perforin, increased at the time of portoenterostomy. Conclusions Perforin and granzymes have complementary roles mediating epithelial injury by NK and CD8 T cells. The prevention of experimental biliary atresia can only be achieved by inhibiting both granules.