Potent virucidal activity in larval Heliothis virescens plasma against Helicoverpa zea single capsid nucleopolyhedrovirus

Abstract

Lepidopteran larvae resist baculovirus infection by selective apoptosis of infected midgut epithelial cells and by sloughing off infected cells from the midgut. Once the infection breaches the midgut epithelial barrier and propagates from infective foci to the haemocoel, however, there are few mechanisms known to account for the resistance and clearance of infection observed in some virus-host combinations. The hypothesis that factors present in the plasma of infected pest larvae act to limit the spread of virus from initial infective foci within the haemocoel was tested. An in vitro bioassay was developed in which Helicoverpa zea single capsid nucleopolyhedrovirus (HzSNPV) was incubated with plasma collected from uninfected Heliothis virescens larvae. Infectious HzSNPV particles were then titrated on HzAM1 cells. Diluted plasma from larval Heliothis virescens exhibited a virucidal effect against HzSNPV in vitro, reducing the TCID 50 ml "1 by more than 64-fold (from 4?3±3?6610 5 to 6?7±0?6610 3 ). The antiviral activity was heat-labile but was unaffected by freezing. In addition, protease inhibitors and specific chemical inhibitors of phenol oxidase or prophenol oxidase activation added to diluted plasma eliminated the virucidal activity. Thus, in the plasma of larval lepidopterans, the enzyme phenol oxidase may act as a constitutive, humoral innate antiviral immune response.

Two arms are better than one: parasite variation leads to combined inducible and constitutive innate immune responses

“…Phenoloxidase activity fulfils the criteria of a constitutive response in that it uses factors that are present without previous contact with a parasite (Brown et al 2003;Popham et al 2004). Further, several invertebrate species have been shown to be plastic in their levels of phenoloxidase activity either in response to selection (Schwarzenbach & Ward 2006) or density dependence .…”

“…The overall effect is the death and melanotic encapsulation of the pathogen very soon after exposure. Although activated by the presence of pathogens, the PO response has been demonstrated to have constitutive properties; previously activated plasma from a larval lepidopteran showed no increased antiviral activity over naive controls (Popham et al 2004). Perhaps the best studied induced responses in insects are the antimicrobial peptides (Hoffmann 2003).…”

Adult honeybees (Apis mellifera L.) abandon hemocytic, but not phenoloxidase-based immunity

“…Thus, we propose the alternative hypothesis that abandoning hemocytic immunity is not restricted to worker honeybees but occurs in all adult honeybees. In addition, constitutive PO activity (Lourenco et al, 2005), which in plasma of larval lepidopterans can inactivate baculoviruses (Popham et al, 2004), might be the candidate immune function to compensate hemocyte loss, if necessary (Rolff, 2001b). In this paper, we report on the outcomes of experiments designed to test these hypotheses.…”

Identification of a Soluble NADPH Oxidoreductase (BmNOX) with Antiviral Activites in the Gut Juice ofBombyx mori

“…Once the infection breaches the midgut epithelial barrier and propagates from infective foci to the hemocoel, however, there are few mechanisms known to account for the resistance and clearance of infection observed in some virus-host combinations. 10) The literature also suggests that insects have evolved digestive enzymes with antiviral properties, as in the case of BmSP-1, BmSP-2, 11) and Bmlipase-1, 12) that check viral propagation at the initial site of viral infection.…”