Host JAK-STAT activity is a target of parasitoid wasp virulence strategies.

Innate immune responses that allow hosts to survive infection depend on the action of multiple conserved signaling pathways. Pathogens and parasites in turn have evolved virulence factors to target these immune signaling pathways in an attempt to overcome host immunity. Consequently, the interactions between host immune molecules and pathogen virulence factors play an important role in determining the outcome of an infection. The immune responses of Drosophila melanogaster provide a valuable model to understand immune signaling and host-pathogen interactions. Flies are commonly infected by parasitoid wasps and mount a coordinated cellular immune response following infection. This response is characterized by the production of specialized blood cells called lamellocytes that form a tight capsule around wasp eggs in the host hemocoel. The conserved JAK-STAT signaling pathway has been implicated in lamellocyte proliferation and is required for successful encapsulation of wasp eggs. Here we show that activity of Stat92E, the D. melanogaster STAT ortholog, is induced in immune tissues following parasitoid infection. Virulent wasp species are able to suppress Stat92E activity during infection, suggesting they target JAK-STAT pathway activation as a virulence strategy. Furthermore, two wasp species (Leptopilina guineaensis and Ganaspis xanthopoda) suppress phenotypes associated with a gain-of-function mutation in hopscotch, the D. melanogaster JAK ortholog, indicating that they inhibit the activity of the core signaling components of the JAK-STAT pathway. Our data suggest that parasitoid wasp virulence factors block JAK-STAT signaling to overcome fly immune defenses. Author summary: Following infection, host immune responses are triggered to provide protection against the invading pathogen. The proper function of these responses depends on the activity of multiple immune signaling pathways. These pathways act in a coordinated manner to orchestrate the immune response, and any disruption can render the host susceptible to infection. Because of this sensitivity, many pathogen species have evolved virulence mechanisms that target host signaling pathways and disrupt their function. We are using the interaction between Drosophila melanogaster and Drosophila-infecting parasitoid wasps to study this relationship between host signaling and pathogen virulence. Parasitoids infect fly larvae, and during infection, transfer virulence protein containing venom into the host, providing a mechanism to alter host signaling. This study is focused on one key immune signaling pathway, the highly conserved JAK-STAT pathway. We find that many virulent parasitoid species restrict the activity of the host JAK-STAT pathway, providing a clue as to their virulence strategy. JAK-STAT signaling plays many additional roles in health and disease, and so this system provides a good model to further understand this important pathway. [ABSTRACT FROM AUTHOR]