Background/purpose: Intraperitoneal inoculation of rhesus rotavirus (RRV) was shown to cause atretic-appearing segments of the extrahepatic bile ducts (EHBDs) in a murine model. The factors responsible for the injury of bile ducts, however, remain unknown. In this study, the morphologic status of nuclear factor- kappa B (NF- kappa B) activation in the liver and in the EHBDs from murine model of biliary atresia induced by intraperitoneal injection of rotavirus was investigated.
Methods: Within the first 24 hours of life, the newborn mice were infected through intraperitoneal route with a volume of 50 microL containing different titers of RRV. The pups were killed on days 5, 10, 15, 21, and 28 after inoculation and prepared under a dissecting microscope with photographic documentation. Consecutive sections of specimens were stained with H & E and used for histopathologic studies. The methods of modified Vision immunohistochemical staining was used to detect viral antigen of VP7 and active NF- kappa B. The distribution and intensity of staining were analyzed by image analysis software (GT-2 model, Huakang Co, Chengdu, China).
Results: The viral antigen was detected by immunohistochemical staining in specimens from experimental groups on day 5 after infection. The occlusion of the EHBDs could be visualized after intraperitoneal injection of 10(7) plaque-forming unit (pfu) of RRV, whereas the incidence of cholestasis was reduced with an infection dosage of 10(6) pfu or less. Obliteration of the EHBDs did not occur when the injection dosage of RRV was reduced to 10(5) pfu or when inoculation of 10(7) pfu of RRV was combined with pyrolidine dithiocarbamate (PDTC), a chemical inhibitor of active NF- kappa B. The antigen of active NF- kappa B was detected by immunohistochemical staining in the liver and in the EHBDs from pups after inoculation of 10(7), 10(6), and 10(5) pfu RRV. Low or no expression of active NF- kappa B was noted in the specimens obtained from the control group. As the inflammatory reaction in the liver and in the EHBDs gradually subsided on day 28 after inoculation, the expression of active NF- kappa B also decreased. The expression of active NF- kappa B after injection of RRV combined with PDTC was similar to the expression in the control group on days 5 and 10 after infection.
Conclusions: The authors found that occlusion of the EHBDs could be noted in pups after inoculation of 10(7) pfu RRV. Meanwhile, the expression of active NF- kappa B in the liver and in the EHBDs was increased after inoculation of RRV. Simultaneous intraperitoneal injection of PDTC, however, was shown to prevent the obstruction of EHBDs secondary to inoculation of RRV. These results show that the murine biliary atresia induced by RRV is mediated by active NF- kappa B.