IL4 and viral infectious disease: Up-regulation of Th1 cytokines (e.g. IL-12, INF-γ) and down-regulation of Th2 cytokines (e.g. IL-4, IL-10) and nitric oxide (NO) were the major targets to retain the th1/th2 balance corrupted by HCV viral infection and have an adequate anti-HCV cellular immune response.