EXCRETORY-SECRETORY PRODUCTS FROM THE ENTOMOPATHOGENIC NEMATODE HETERORHABDITIS BACTERIOPHORA ENHANCE THE SUSCEPTIBILITY OF DROSOPHILA TO BACTERIAL INFECTION VIA SUPPRESSION OF THE Imd IMMUNE SIGNALING PATHWAY.
Eric Kenney, The George Washington University
Eric Kenney1, Jonathan Vadnal1, John M. Hawdon2, Damien O’ Halloran1, and Ioannis Eleftherianos1.
Department of Biological Sciences1, Department of Microbiology, Immunology, and Tropical Medicine2 The George Washington University, Washington, DC.
In order to promote the success of an infection, parasitic helminths are known to secrete factors that manipulate the host immune system. A variety of applications await the identification of these factors, including the enhancement of entomopathogens used for the biocontrol of insect pests and the counter-suppression of vertebrate-infective helminths, but prerequisite to this identification is a foundational understanding of the total immunomodulatory capacities of the parasite. To this aim, infective juveniles (IJs) of the entomopathogen Heterorhabditis bacteriophora were activated in insect hemolymph before bulk secretions were collected and concentrated. Secreted products were then injected into Drosophila melanogaster flies, revealing through qPCR measurements distinct suppression of the Imd pathway, which serves as the primary signaling mechanism for coordinating an immune response against gram-negative bacteria. In conjunction with observations that the Toll pathway is not affected by the injection of secretions and that secretions from non-activated nematodes significantly increase Imd-based expression, the Imd pathway can be implicated as a primary axis of the immune response against a helminth infection. Furthermore, co-injection of the secreted products along with gramnegative bacteria enhanced the susceptibility of flies to bacterial infection, despite the tendency of activated secretions to enhance phagocytic activity in flies, as measured by pHrodo E.coli conjugate injections. Together, these data indicate that H. bacteriophora secretes products that modulate the Drosophila immune response and that these secretions may serve to promote the efficacy of H. bacteriophora’s symbiotic gram-negative bacteria and fellow entomopathogen, Photorhabdus luminescens.