 RBV is another antiviral nucleotide analogue with few adverse effects Sidwell et al, 1972; Patterson et al, 1990. RBV alone can modestly inhibit HDV or HBV replication Choi et al, 1989. The beneficial effect of combined IFN plus RBV in the treatment of chronic hepatitis B has also been shown in previous studies Cotonat et al, 2000. Why RBV can greatly enhance the treatment efficacy is not clear. It had been shown that ribavirin could inhibit interleukin-4, an inhibitor of cytotoxic T lymphocyte activity, and preserves the interleukin-2 and gamma IFN activities. Other studies revealed that the enhanced efficacy was associated with HBV- or other virus-specific type 1 cytokine-mediated T helper cell responses Cramp et al, 2000; Tam et al, 1999; Hultgren et al, 1998; Fang et al, 2002; Fang et al, 2000; Rico et al, 2001. Thus, the combination therapy may augment virus-specific cytotoxic T lymphocytes and non-specific immune response, and effectively shift the immune responses to the more potent antiviral type 1 T-helper profile Hultgren et al, 1998. 