Dissecando aspectos da resposta antiviral utilizando o modelo da mosca Drosophila melanogaster

Abstract

The diseases caused by arboviruses, such as dengue, have a great impact on global public health. Arboviruses are transmitted to vertebrate hosts by invertebrate vectors where they must interact with the immune system. Thus, understanding insect antiviral immune pathways could help the design of strategies to control arbovirus transmission. Immunity against viruses in insects is mainly mediated by RNA interference (RNAi) pathway which is activated by recognition of double-stranded RNA (dsRNA) originating from intermediates of viral replication. This recognition leads to the production of small interfering RNAs (siRNAs) that associate with Argonaute family proteins to form a complex that promotes the degradation of viral transcripts. Other insect immune pathways, such as JAK-STAT, Toll and IMD may also be involved in the antiviral response. During outbreaks, the insect vector could be exposed to multiple infections by the same virus. We should also consider that insects can naturally carry one or more different viruses infections. Thus, our main objective in this work was to characterized the effect of co-infections on the interaction between arbovirus and the insect vector. We investigated whether prior exposure to a virus could have an impact on a secondary infection. As a model of infection, we used the fruit fly Drosophila melanogaster infected with the arbovirus Vesicular stomatitis virus (VSV). To differentiate the virus used in the first and in the second infection, we used a virus capable of expressing GFP as a reporter. In this model, we observed interference on the replication of the second virus by the first infection. This effect is dependent of the dose and the time of viral infection suggesting that it is mediated by a saturable mechanism. The interference was also observed in RNAi defective flies indicating that the main antiviral pathway of insects is not involved in this phenomenon. We also observed that the interference is not virus-specific, because the same phenomenon is observed when a heterologous virus, SINV (Sindibis virus), was used. This result is in accordance with the independence of the RNAi pathway, since the antiviral siRNAs would be specific for each virus. We also measured the expression of marker genes in different groups of infected flies in order to examine whether signaling pathways such Jak-STAT would be differentially activated. However, there was no significant difference in the expression of marker genes after the second infection in pre-infected or control flies. Although preliminary, this result suggests that the inductin of virus- responsive genes does not explain the interference. Our work has mostly focused on possible mechanisms of interference mediated by the host response. However, it is also possible that there may be direct interference of the first virus on the replication of the second. Further work using mutant flies in other immune pathways as well as other pathogens will be needed to define the mechanism of interference described here.