Molecular and cellular processes of the innate immune response in insects: investigation on the immune modulation induced by entomopathogenic nematodes

Aim of this project was to investigate relationships between Rhynchophorus ferrugineus or Galleria mellonella and the entomopathogenic nematode Steinernema carpocapsae. In particular, the work was focused on the immune response of the insect host either in naïve larvae or in larvae infected with entomoparasites. We analyzed different immunological processes: the activity and modulation of prophenoloxidase-phenoloxidase (proPO) system, the cell-mediated encapsulation, the antimicrobial peptides (AMPs) inducible response and finally the phagocytosis activity of the host hemocytes. Furthermore, we investigated the immune depressive and immune evasive strategies of the parasite. Our results indicated that R. ferrugineus has an efficient immune system; however, in the early phase of infection, the presence of S. carpocapsae induces a strong inhibition of the host proPO system. In addition, the parasite does not seem to be susceptible to the encapsulation by host hemocytes; the parasite mimetic properties seem to be related to the structure of its body surface. S. carpocapsae, before the release of its symbiotic bacteria (X. nematophila), depresses and elude the host immune defenses, with the aim to create a favorable environment for its symbionts responsible of the septicemic death of the insect host. Besides, our results have demonstrated that X. nematophila is able to inhibit the synthesis and the activity of antimicrobial peptides. X .nematophila elude the recognition by hemocytes since it is not engulfed by the host cells. It is evident that the nematode and its symbiotic bacteria cooperate to elude and inhibit immune responses of the insect host. This study provides data that can help to a better understand of the relationships between parasites and their hosts.