The activity of phenoloxidase in haemolymph plasma is not a predictor of Lymantria dispar resistance to its baculovirus

PLoS One. 2017 Aug 30;12(8):e0183940. doi: 10.1371/journal.pone.0183940. eCollection 2017.

Abstract

Host innate immunity is one of the factors that determines the resistance of insects to their entomopathogens. In the research reported here we studied whether or not phenoloxidase (PO), a key enzyme in the melanogenesis component of humoral immunity of insects, plays a role in the protection of Lymantria dispar larvae from infection by L. dispar multiple nucleopolyhedrovirus. We studied two types of viral infection: overt and covert. The following lines of investigation were tested: i) the intravital individual estimation of baseline PO activity in haemolymph plasma followed by virus challenging; ii) the specific inhibition of PO activity in vivo by peroral treatment of infected larvae with phenylthiourea (PTU), a competitive inhibitor of PO; iii) the evaluation of PO activity in the haemolymph plasma after larval starvation. Starvation is a stress that activates the covert infection to an overt form. All of these experiments did not show a relationship between PO activity in haemolymph plasma of L. dispar larvae and larval susceptibility to baculovirus. Moreover, starvation-induced activation of covert viral infection to an overt form occurred in 70 percent of virus-carrying larvae against the background of a dramatic increase of PO activity in haemolymph plasma in the insects studied. Our conclusion is that in L. dispar larvae PO activity is not a predictor of host resistance to baculovirus.

MeSH terms

  • Animals
  • Hemolymph / enzymology*
  • Hemolymph / virology*
  • Host-Pathogen Interactions*
  • Monophenol Monooxygenase / metabolism*
  • Moths / enzymology*
  • Moths / virology*
  • Nucleopolyhedroviruses / physiology*

Substances

  • Monophenol Monooxygenase

Grant support

The work was supported by Civilian Research and Development Foundation (RUB1-2922-NO-07); and Russian foundation for basic research (08-04-91116 and 15-04-08197). The study of PO inhibition by PTU was supported by the Russian Science Foundation (grant Nr 15-14-10014). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.