Dengue virus antagonism of the Aedes aegypti IMD immune response.

Dengue virus (DENV) is the most significant arthropod-borne virus (arbovirus) of humans, primarily transmitted by Aedes aegypti mosquitoes. Currently there are no specific therapeutics and the existing vaccine exhibits limited efficacy. Therefore, vector control remains the best approach to manage disease spread. We previously demonstrated that DENV-2 infection does not induce innate immunodeficiency (IMD) signalling in the Ae. aegypti Aag2 cell line, recapitulating in vivo data from other groups. Furthermore, prior infection with DENV-2 reduces IMD signalling activation by classical immune stimuli. This project aimed to identify DENV-2 antagonist(s) responsible for this immune inhibition using an RT-qPCR-based screening platform in which IMD signalling is stimulated in cells expressing DENV-2 proteins individually. Our results identified NS4A as a tentative antagonist, which can now be used to enhance our understanding of Ae. aegypti antiviral immunity by investigating virus-host interactions. The study of vector immunity is hampered by the lack of tools such as antibodies and cell lines. Our group previously created CRISPR-Cas9 knockout Aag2 cell lines, which lack genes essential in the innate immune pathways. These knockout cell lines were created from clonally selected Aag2 cells derived from the heterogeneous parental cell line, and this report also describes the final characterisation of these clones. Results confirm that the cells are embryonic in origin, which confounded our sex analysis. Aag2 clones were confirmed to be persistently infected insect-specific viruses, cell fusing agent virus and Phasi Charoen-like virus. Transfection efficiencies were also determined for the clones of interest. Finally, mutations introduced by CRISPR-Cas9 were characterised in cells derived from one of the clonally selected lines, with one clone identified as the intended mutant, however the IMD pathway-deficient cell clones were determined as wild type. Ultimately insights into vector antiviral immunity may contribute towards development of transmission-incompetent mosquitoes, thereby reducing the global burden of dengue.