Anopheles gambiae Antiviral Immune Response to Systemic O'nyong-nyong Infection

Abstract

Background Mosquito-borne viral diseases cause significant burden in much of the developing world. Although host-virus interactions have been studied extensively in the vertebrate host, little is known about mosquito responses to viral infection. In contrast to mosquitoes of the Aedes and Culex genera, Anopheles gambiae , the principal vector of human malaria, naturally transmits very few arboviruses, the most important of which is O'nyong-nyong virus (ONNV). Here we have investigated the A. gambiae immune response to systemic ONNV infection using forward and reverse genetic approaches. Methodology/Principal Findings We have used DNA microarrays to profile the transcriptional response of A. gambiae inoculated with ONNV and investigate the antiviral function of candidate genes through RNAi gene silencing assays. Our results demonstrate that A. gambiae responses to systemic viral infection involve genes covering all aspects of innate immunity including pathogen recognition, modulation of immune signalling, complement-mediated lysis/opsonisation and other immune effector mechanisms. Patterns of transcriptional regulation and co-infections of A. gambiae with ONNV and the rodent malaria parasite Plasmodium berghei suggest that hemolymph immune responses to viral infection are diverted away from melanisation. We show that four viral responsive genes encoding two putative recognition receptors, a galectin and an MD2-like receptor, and two effector lysozymes, function in limiting viral load. Conclusions/Significance This study is the first step in elucidating the antiviral mechanisms of A. gambiae mosquitoes, and has revealed interesting differences between A. gambiae and other invertebrates. Our data suggest that mechanisms employed by A. gambiae are distinct from described invertebrate antiviral immunity to date, and involve the complement-like branch of the humoral immune response, supressing the melanisation response that is prominent in anti-parasitic immunity. The antiviral immune response in A. gambiae is thus composed of some key conserved mechanisms to target viral infection such as RNAi but includes other diverse and possibly species-specific mechanisms.

Antiviral immunity of Anopheles gambiae is highly compartmentalized, with distinct roles for RNA interference and gut microbiota

“…In previous analyses of the An. gambiae immune response to arbovirus infection, ONNV was delivered by intrathoracic injection (6,28) or by feeding mosquitoes on an infectious blood meal (29). Blood feeding is the natural route of virus entry, but the latter study analyzed the mosquito response only at 14 d PBM, which consequently, as mentioned above, analyzed the systemic response to a disseminated infection and not the initial midgut response.…”

Antiviral responses of arthropod vectors: an update on recent advances

“…SFV was able to activate PO in U4.4 cell-conditioned medium with similar efficiency to E. coli and, when a suppressor of the PO pathway was inserted into the SFV genome, virus replication was increased in A. aegypti mosquitoes [97]. Another study showed that ONNV infection of A. gambiae reduced expression of components of the melanisation cascade and in co-infection studies ONNV infection inhibited melanisation of Plasmodium ookinetes [125]. Thus it is possible that A. gambiae PO has antiviral activity and that ONNV has evolved to counteract this mechanism.…”

“…The study performed with SINV in Drosophila used whole flies; however, Drosophila is not a blood-feeding vector of arboviruses and thus may lack mechanisms evolved specifically against vector-borne alphaviruses. In A. gambiae concurrent injection of ONNV and dsRNA against Cactus resulted in an increased viral load 7 days post-injection compared to dsRNA controls which did not target Cactus [125]. If the Toll pathway was involved in controlling alphavirus replication in mosquitoes, knocking down expression of cactus, as a negative regulator of the pathway, should result in a decrease of virus replication.…”

“…Preactivation of the Imd pathway by heat-inactivated E. coli also increased SFV replication in U4.4 cells [33]. In the mosquito A. gambiae, ONNV infection led to changes in expression of Imd pathway components, possibly activating the Imd pathway, but since knockdown of REL2 gene expression did not affect virus production, the role of Imd in ONNV infection remains unclear [125].…”

Compartimentation de la réponse immunitaire chez le moustiqueAnopheles gambiae

“…Cela nous a permis de déterminer le moment adéquat pour évaluer la réponse antivirale intestinale, avant la dissémination du virus dans le reste de l'organisme. Lors des études précédentes sur l'immunité antivirale des moustiques Anopheles, le virus était directement injecté dans le thorax des insectes, comme cela se fait pour l'organisme modèle qu'est la drosophile [7][8][9], court-circuitant ainsi la barrière physique et immune que forme l'épithé-lium intestinal. En comparant les réponses antivirales de l'intestin et du compartiment systé-mique (après injection du virus in vivo ou utilisation de lignées cellulaires), nous avons montré que, contrairement à ce qui était précédemment admis [7][8][9], l'ARN interférence (ARNi) ne joue pas de rôle antiviral dans l'intestin du moustique et n'intervient que secondairement dans le une double composante, temporelle et spatiale, importante à considérer lors de l'étude des interactions du virus avec les réponses antivirales du moustique.…”