PHOTOINACTIVATION OF INFLUENZA VIRUS FUSION AND INFECTIVITY BY ROSE BENGAL

Rose bengal inactivated influenza virus upon exposure to light. Infectivity and fusion were inactivated with the same dose dependence, supporting the suggestion that the virucidal activity of photodynamic agents against enveloped viruses may be generally due to inactivation of their fusion protein(s). Concentrations required for inac-ti vation were found to depend upon the ratio of rose bengal to virus, rather than on the nominal aqueous concentration. Fusion-competent virosomes were inactivated similarly to intact virus particles. The HA_Z portion of the influenza fusion protein HA underwent two different, apparently mutually exclusive modifications upon illumination with rose bengal: cross-linking, and conversion to a form that moved slightly more slowly on sodium dodecyl sulfate poly-acrylamide gel electrophoresis. Inactivation of viral fusion was inhibited by oxygen removal or addition of azide or β-carotene, and was enhanced by D₂O, consistent with partial involvement of singlet oxygen. The possibility of a second mechanism of viral photoinactivation, by direct interaction between the viral fusion protein and the pho-toactivated dye, is also discussed.