Response of immunocompetent and immunosuppressed Spodoptera littoralis larvae to baculovirus infection

Abstract

The Mediterranean lepidopteran pest Spodoptera littoralis is highly resistant to infection with the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) via the oral route, but highly sensitive to infection with budded virus (BV) via the intrahaemocoelic route. To study the fate of AcMNPV infection in S. littoralis, vHSGFP, an AcMNPV recombinant that expresses the reporter green fluorescent protein gene under the control of the Drosophila heat-shock promoter, and high-resolution fluorescence microscopy were utilized. S. littoralis fourth-instar larvae infected orally with vHSGFP showed melanization and encapsulation of virus-infected tracheoblast cells serving the midgut columnar cells. At 72 h post-infection, the viral foci were removed during the moult clearing the infection. Thus, oral infection was restricted by immune responses to the midgut and midgut-associated tracheal cells. By contrast, injection of BV into the haemocoel resulted in successful infection of tracheoblasts, followed by spread of the virus through the tracheal epidermis to other tissues. However, in contrast to fully permissive infections where tracheoblasts and haemocytes are equally susceptible to infection, a severe limitation to vHSGFP infection of haemocytes was observed. To investigate the resistance of S. littoralis haemocytes to BV infection with AcMNPV, the larval immune system was suppressed with the Chelonus inanitus polydnavirus or a putatively immunosuppressive polydnavirus gene, P-vank-1. Both treatments increased the susceptibility of S. littoralis larvae to AcMNPV. It is concluded that the resistance of S. littoralis to AcMNPV infection involves both humoral and cellular immune responses that act at the gut and haemocyte levels. The results also support the hypothesis that tracheolar cells mediate establishment of systemic baculovirus infections in lepidopteran larvae. The finding that polydnaviruses and their encoded genes synergize baculovirus infection also provides an approach to dissecting the responses of the lepidopteran immune system to viruses by using specific polydnavirus immunosuppressive genes.

Pathogenesis of Lymantria dispar multiple nucleopolyhedrovirus in L. dispar and mechanisms of developmental resistance

“…In non-or semi-susceptible hosts, cellular immune responses to AcNPV-infected tissues can occur (Rivkin et al, 2006;Trudeau et al, 2001;Washburn et al, 2000). Haemocytes of some hosts are refractory to AcNPV infection and replication, which slows or stops the spread of the virus within the haemocoel (Rivkin et al, 2006). Apoptosis of AcNPV-infected cells can also serve as an antiviral response (Clarke & Clem, 2003;da Silveira et al, 2005;Zhang et al, 2002).…”

“…Hoover et al (2002) hypothesized that immune responses play a role in systemic resistance in L. dispar. In non-or semi-susceptible hosts, cellular immune responses to AcNPV-infected tissues can occur (Rivkin et al, 2006;Trudeau et al, 2001;Washburn et al, 2000). Haemocytes of some hosts are refractory to AcNPV infection and replication, which slows or stops the spread of the virus within the haemocoel (Rivkin et al, 2006).…”

Interactions Between Nucleopolyhedroviruses and Polydnaviruses in Larval Lepidoptera

“…In non-or semi-susceptible hosts, cellular immune responses to AcNPV-infected tissues can occur (Rivkin et al, 2006;Trudeau et al, 2001;. Haemocytes of some hosts are refractory to AcNPV infection and replication, which slows or stops the spread of the virus within the haemocoel (Rivkin et al, 2006). Apoptosis of AcNPV-infected cells can also serve as an antiviral response (Clarke & Clem, 2003;da Silveira et al, 2005;Zhang et al, 2002).…”

“…Hoover et al, (2002) hypothesized that immune responses play a role in systemic resistance in L. dispar to LdMNPV. In non-or semi-susceptible hosts, cellular immune responses to AcNPV-infected tissues can occur (Rivkin et al, 2006;Trudeau et al, 2001;. Haemocytes of some hosts are refractory to AcNPV infection and replication, which slows or stops the spread of the virus within the haemocoel (Rivkin et al, 2006).…”

Tissue specificity of a baculovirus-expressed, basement membrane-degrading protease in larvae of Heliothis virescens

“…will provide a control for this (Rivkin et al, 2006). AcMLF9.ScathL.C146A.Pvankyrin1 (HPS.C), both the vankyrin and ScathL.C146A were expressed correctly at 35 and 45 Kda for ScathL.C146A and at 19 kDa for Pvank-1 (Kroemer and Webb, 2005 ScathL, AcMLF9.ScathL; C146A, AcMLF9.ScathL.C146A; P-Van-1, P-vankyrin-1 expressing virus; I 2 -Van-3, I 2 -vankyrin-3 expressing virus.…”