Pathogenesis of experimental neonatal woodchuck hepatitis virus infection: Chronicity as an outcome of infection is associated with a diminished acute hepatitis that is temporally deficient for the expression of interferon gamma and tumor necrosis factor-alpha messenger RNAs

Surgical biopsies of the liver were obtained from woodchuck hepatitis virus (WHV)–infected neonatal woodchucks at 2 time points before the self–limited or chronic outcomes became obvious by serologic criteria. Following segregation of outcomes, livers were analyzed for intrahepatic type 1 cytokine messenger RNAs (mRNAs) (interleukin 2 [IL–2], interferon gamma [IFN–γ], tumor necrosis factor–alpha [TNF–α]) and leukocyte inflammatory phenotype (IgG + plasma cells, lysozyme + macrophages, CD3 + T cells). Baselines were assessed using age–matched uninfected control livers. At week 8 (early acute phase), intrahepatic type 1 cytokine mRNAs were similarly low in both outcome settings and no different from age–matched uninfected controls. This was consistent with the minimal initial viral loads and lack of histologic inflammation at this time. At week 14 (mid–acute phase), changes in viral load between outcome groups related inversely to the intrahepatic inflammatory responses. Animals that eventually became resolved had increased intrahepatic expression of IFN–γ and TNF–α mRNAs and robust inflammation by CD3 + T cells, plasma cells, and macrophages. At the same time point of infection, animals that eventually became chronic carriers had an acute hepatitis involving the same cell types, but at diminished levels, and markedly deficient intrahepatic expression of IFN–γ and TNF–α mRNAs. IL–2 mRNA remained at baseline control levels in both outcome groups. These cotemporal comparisons map a critical deviation in host response to the acute stage of an evolving chronic infection. They strongly suggest that increasing viral load and chronicity as an outcome of neonatal WHV infection result from a temporal deficiency in the acute intrahepatic effector mechanisms mediated by IFN–γ and TNF–α.