Insect Antiviral Innate Immunity: Pathways, Effectors, and Connections

Abstract

Insects are infected by a wide array of viruses some of which are insect-restricted and pathogenic, and some of which are transmitted by biting insects to vertebrates. The medical and economic importance of these viruses heightens the need to understand the interaction between the infecting pathogen and the insect immune system in order to develop transmission interventions. The interaction of the virus with the insect host innate immune system plays a critical role in the outcome of infection. The major mechanism of antiviral defense is the siRNA pathway that responds through the detection of virus-derived dsRNA to suppress virus replication. However, other innate antimicrobial pathways such as Imd, Toll, Jak-STAT, and the autophagy pathway have also been shown to play important roles in antiviral immunity. In this review we provide an overview of the current understanding of the main insect antiviral pathways and examine recent findings that further our understanding of the roles of these pathways in facilitating a systemic and specific response to infecting viruses.

A mutualistic symbiosis between a parasitic mite and a pathogenic virus undermines honey bee immunity and health

“…Separate independent work further corroborated this evidence, showing that viral infection in honey bees interfered with the expression of genes that participate in the Toll pathway (11,12). This finding supports the hypothesis that in honey bees, and more generally in insects, inducible antiviral barriers besides RNAi-mediated mechanisms (11)(12)(13)(14)(15)(16)(17)(18) may have an important role. Indeed, in collapsing colonies, these latter barriers under NF-κB or JAK-STAT control appear to be targeted, whereas the RNAi machinery seems to be unaffected (19).…”

Antiviral responses of arthropod vectors: an update on recent advances

“…All of the three major innate immunity signalling pathways in insects, namely Janus kinase/signal transducer and activator of transcription (JAK/STAT), Toll and Immune deficiency (Imd), have been implicated in antiviral defences in insects (reviewed by [34,62,81] ). All three pathways also play a role in development and especially in immune responses to other pathogens.…”

“…A downstream signalling cascade [62,81] (Fig. 1) results in activation of REL2 [106], another orthologue of NFjB.…”

“…Besides RNAi and signalling pathways there are many other responses in arthropods to virus infection including melanisation [97] and cell stress responses such as autophagy and regulation of heat shock proteins (reviewed by [62,81]). However, since heat-shock proteins are important for loading siRNA into the RISC in Drosophila [57], upregulation of heat-shock proteins may not be an antiviral response in itself, but a necessary step for efficient antiviral RNAi.…”

“…In the 2005-2006 outbreak of chikungunya fever on the Indian Ocean island of La Reunion, rapid replication and dissemination of this infection was associated with a single point mutation in the viral envelope glycoprotein which adapted the virus to replicate in and to be disseminated by anthropophilic Aedes albopictus mosquitoes [121]. All arboviruses have to deal with at least two very different immune systems and, while research into and knowledge of arbovirus-host interaction in vertebrate systems is well developed, knowledge of vector antiviral responses has been gained principally over the last 10 years [32,34,62,81]. This review aims to summarise knowledge to date about antiviral responses of arthropod vectors to arboviruses.…”