APOBEC and iNOS are not the main intracellular effectors of IFN-gamma-mediated inactivation of Hepatitis B virus replication. 
Interferon-gamma (IFN-gamma) produced by activated T-cells is the principle mediator of non-cytolytic Hepatitis B virus (HBV) inactivation; however the intracellular pathways responsible are poorly defined.  We investigated the role of IFN-gamma-inducible nitric oxide synthase (iNOS) and APOBEC3 (A3) enzyme family in the inhibition of HBV replication by IFN-gamma.  Hepatoma-cell lines transfected with HBV DNA were treated with IFN-gamma.  Viral replication, iNOS and A3 mRNAs were quantitated by TaqManPCR and the direct nitric oxide (NO) effect on HBV replication was investigated using an NO-donor.  A3G antiviral activity was verified by co-transfection with its inhibitor, human immunodeficiency virus (HIV)-associated virion infectivity factor (Vif).  IFN-gamma caused a dose-dependent reduction (>50%) of HBV DNA in the absence of cytotoxicity.  Although iNOS mRNA increased 45-fold in IFN-gamma treated cells, NO2- was not detectable in supernatants and the use of an NO-donor did not inhibit HBV replication.  A3 enzyme mRNAs varied between cells and were >10-fold higher in lymphocytes than in liver tissue.  IFN-gamma up-regulated A3G mRNA by three-fold, associated with significant HBV DNA decrease.  However, A3G degradation by Vif did not abolish the antiviral effect of IFN-gamma against HBV.  IFN-gamma inhibits HBV replication and up-regulates both iNOS and A3G. However, other pathways appear to have a greater role in IFN-gamma-induced HBV inactivation in the liver.