Heterorhabditis bacteriophora Extracellular Vesicles Alter the Innate Immune Signaling in Drosophila melanogaster

<b>Background:</b><i>Heterorhabditis bacteriophora</i> entomopathogenic nematodes are commonly used in agricultural practices for the biological control of insect pests. These parasites are also used in basic research for unveiling the molecular basis of nematode parasitism in relation to the insect anti-nematode response. We have recently shown that <i>H. bacteriophora</i> excreted-secreted products reduce the expression of the antimicrobial peptide gene <i>Diptericin</i> in <i>Drosophila melanogaster</i>, which increases fly mortality due to enhanced propagation of the mutualistic bacteria <i>Photorhabdus luminescens</i>. However, the effect of entomopathogenic nematode extracellular vesicles (EVs) on the insect host defense remains unknown. <b>Methods:</b> Here, we injected adult flies with <i>H. bacteriophora</i> EVs and used quantitative RT-PCR together with gene-specific primers to analyze the activity of immune-related signaling pathways. <b>Results:</b> We found that <i>H. bacteriophora</i> EVs are lethal to <i>Drosophila melanogaster,</i> and they downregulate the expression of <i>Attacin</i>, <i>Cecropin,</i> and <i>Prophenoloxidase 3</i> in adult flies. <b>Conclusions:</b> These findings build on previous knowledge and strengthen the notion that <i>H. bacteriophora</i> entomopathogenic nematodes release a variety of effector molecules to modify the insect's innate immune signaling. This information is important because it contributes toward clarifying the molecular interplay between entomopathogenic nematode components and the host's innate immune system.