Macrophage-mediated inhibitory effect of Zingiber officinale Rosc, a traditional Oriental herbal medicine, on the growth of influenza A/Aichi/2/68 virus

The inhibitory effect of Zingiber officinale Rosc (ZOR), an Oriental traditional herbal medicine, on the growth of influenza A/Aichi/2/68 (Aichi) virus was investigated in Madin-Darby canine kidney (MDCK) cells. Direct addition of ZOR (0.1 ∼ 100 μg/ml) to the infected cells did not have any inhibitory effect. However, the ZOR-induced conditioned medium (ZOR-CM) of RAW cells, a murine macrophage (Mφ) cell line, exhibited an apparent inhibitory effect on MDCK cells without cytotoxicity. In accordance with the time-dependent inhibitory effect of ZOR-CM, it has been demonstrated that tumor necrosis factor (TNF)-α was gradually accumulated in ZOR-CM by the induction of TNF-α mRNA expression in ZOR-stimulated RAW cells. Conversely, the inhibitory effect of ZOR-CM was reduced significantly by the removal of TNF-α after the formation of an immune complex with anti-TNF-α monoclonal antibody. These data suggested that ZOR itself has no inhibitory effect on the growth of influenza virus, but could exert its effect via macrophage activation leading to production of TNF-α.