The Aedes aegypti Toll Pathway Controls Dengue Virus Infection

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Abstract
Aedes aegypti, the mosquito vector of dengue viruses, utilizes its innate immune system to ward off a variety of pathogens, some of which can cause disease in humans. To date, the features of insects' innate immune defenses against viruses have mainly been studied in the fruit fly Drosophila melanogaster, which appears to utilize different immune pathways against different types of viruses, in addition to an RNA interference–based defense system. We have used the recently released whole-genome sequence of the Ae. aegypti mosquito, in combination with high-throughput gene expression and RNA interference (RNAi)-based reverse genetic analyses, to characterize its response to dengue virus infection in different body compartments. We have further addressed the impact of the mosquito's endogenous microbial flora on virus infection. Our findings indicate a significant role for the Toll pathway in regulating resistance to dengue virus, as indicated by an infection-responsive regulation and functional assessment of several Toll pathway–associated genes. We have also shown that the mosquito's natural microbiota play a role in modulating the dengue virus infection, possibly through basal-level stimulation of the Toll immune pathway. The Aedes aegypti mosquito is largely responsible for the transmission of dengue viruses that cause disease in humans. The virus is taken up with an infected blood meal from which it will first infect the mosquito gut tissue. From the gut it will migrate to other parts of the mosquito, including the salivary glands, from where it can be transmitted to another human upon a second blood meal. In this study we show that the mosquito utilizes its innate immune system to control dengue virus infection. Infection with the virus will result in the activation of mosquito immune responses that are mainly controlled by the Toll pathway. These responses entail antiviral activities that limit infection with the virus. We also show that the mosquito's natural microbial flora play a role in modulating the dengue virus infection, possibly through the stimulation of the mosquito's immune system.