Submitted to: American Society for Virology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 23, 2005
Publication Date: July 21, 2005
Citation: Shelby, K., Popham, H.J. 2005. Virucidal activity in the plasma of larval lepidopteran [abstract]. American Society for Virology Meeting. p. 166. Technical Abstract: Heliothis virescens larval plasma contains high levels of an antiviral activity against Helicoverpa zea single nucleopolyhedrovirus (HzSNPV) budded virus in vitro. Preliminary results indicated that phenoloxidase is primarily responsible for this virucidal effect. However it is known that other enzymes which generate antimicrobial reactive oxygen intermediates and reactive nitrogen intermediates are present in hemolymph which could contribute to the observed virucidal activity. To elucidate the contributions of phenoloxidase and other candidate activities to plasma innate immune response against baculovirus infection, we have used specific metabolic inhibitors. In vitro the general inhibitors of melanization, and specific inhibitors of phenoloxidase, completely blocked virucidal activity up to the level seen in controls. Addition of the enzyme catalase to plasma did not affect virucidal activity; however addition of superoxide dismutase exhibited a modest inhibitory effect. Pull-down assays in which plasma phenoloxidase was depleted from samples using increasing concentrations of rabbit polyclonal anti-PO antisera reduced virucidal activity in a concentration dependent manner. Inhibitors of nitric oxide synthase activity did not affect virucidal activity. Our results confirm that phenoloxidase is the predominate activity in larval plasma accounting for inactivation of HzSNPV in vitro, and that phenoloxidase-dependent superoxide production may contribute to this virucidal activity. Dietary factors that impact phenoloxidase activity will be discussed.