Hemocytes control dengue virus systemic infection through RNAi pathway

Dengue is the most important arboviral disease since its prevalence has increased 30-fold during the last 50 years. The primary vector is the Aedes aegypti mosquito, which has a robust immune system that protects them against several pathogens including viruses. Hemocytes are one of the most important cell types of the mosquito immune system because they carry out critical and exclusive functions that kill pathogens such as bacteria, fungi, and protozoa. Recent studies suggest that hemocytes are important for controlling viral infection, however, the mechanisms by which hemocytes mediate antiviral immunity are poorly understood. In this study, we assessed the role of hemocytes in dengue virus type 2 (DENV2) infection. We chemically depleted hemocytes in mosquitoes and discovered that these cells do not influence controlling midgut infection; however, the systemic viral titer was higher, indicating that hemocytes may be involved in regulating viral systemic infections. By a transcriptomics analysis of hemocytes from DENV2-infected mosquitoes, we discovered upregulated genes related to miRNA and piRNA pathways. By using RNA interference to silence some of these genes, we discovered that SAFB2 and PIWI4 gene knockdown led to an increase in systemic viral titers, indicating that hemocytes regulate viral systemic infection by miRNA and piRNA pathways. We conclude that hemocytes play an important role in controlling systemic DENV2 infection. Dissemination of the virus from the midgut to the salivary glands is a critical step for transmission of arbovirus, and hemocytes could play a crucial role in limiting the transmission of these pathogens.