The role of Steinernema feltiae body-surface lipids in host-parasite immunological interactions.

Interactions between entomopathogenic nematodes (Steinernema feltiae) and insect host (Galleria mellonella) immune system were investigated. We focused on the immunosuppressive properties of the parasite cuticle and on its interaction with hemolymph humoral components. Effects of parasite cuticle against host proPO system enzymatic cascade were evaluated a short time after infection. The presence of parasite cuticles decreased both normal and LPS-elicited proPO system activity, suggesting that S. feltiae body surface plays a key role in the early parasitation phase, probably interfering with host proPO activation pathways. The data obtained showed that cuticle lipidic compounds are able to interact with host humoral components, removing them from the hemolymph. The depletion of these molecules, arbitrarily named host-interacting proteins (HIPs), seems to be responsible of the drastic decrease in proPO system activity. Moreover, hemolymph HIPs showed LPS-binding properties and parasite cuticle cross-reacted with anti-LPS antibodies. Finally, we also assessed the involvement of parasite body surface on immunoevasion strategies of S. feltiae against host cell-mediated encapsulation processes. We conclude that S. feltiae body surface is responsible for short-term immunosuppression and immunoevasion processes; since it is able to sequester host hemolymph compounds involved in proPO system activation and this process could be responsible for a molecular disguise strategy against cellular encapsulation.