Abstract
Aedes albopictus is a major vector of dengue (DENV) and chikungunya (CHIKV) viruses, causing millions of infections annually. It naturally carries, at high frequency, the intracellular inherited bacterial endosymbiont Wolbachia strains wAlbA and wAlbB; transinfection with the higher-density Wolbachia strain wMel from Drosophila melanogaster led to transmission blocking of both arboviruses. The hypothesis that reactive oxygen species (ROS)-induced immune activation plays a role in arbovirus inhibition in this species was examined. In contrast to previous observations in Ae. aegypti, elevation of ROS levels was not observed in either cell lines or mosquito lines carrying the wild-type Wolbachia or higher-density Drosophila Wolbachia strains. There was also no upregulation of genes controlling innate immune pathways or with antioxidant/ROS-producing functions. These data suggest that ROS-mediated immune activation is not an important component of the viral transmission-blocking phenotype in this species.
Highlights
Wolbachia are maternally transmitted, intracellular bacterial endosymbionts that can spread to high frequency in insect populations by manipulating their reproduction, in particular using patterns of sterility known as cytoplasmic incompatibility to give a reproductive advantage to Wolbachia-infected females [1]
No significant elevation of reactive oxygen species (ROS) levels or differential regulation of any of the innate immune pathway regulator genes or of antioxidant/ROS-modulating genes was demonstrated in Ae. albopictus, except that in cell lines STAT was sometimes upregulated
These results suggest that the hypothesis of ROS-induced Toll pathway activation is responsible for DENV inhibition in Ae. aegypti [11] does not apply in Ae. albopictus
Summary
Intracellular bacterial endosymbionts that can spread to high frequency in insect populations by manipulating their reproduction, in particular using patterns of sterility known as cytoplasmic incompatibility to give a reproductive advantage to Wolbachia-infected females [1]. Aedes aegypti [8,9], and expanded trials of the use of Wolbachia for arbovirus control are planned or underway. In this context it is important to gain a better understanding of the mechanisms by which the bacterium can inhibit virus transmission. In Wolbachia-transinfected Ae. aegypti, chronic upregulation of insect innate immune pathways, including antimicrobial peptides (AMPs) and other immune effectors has been observed and may play a role in the inhibition of arboviruses [2,3,10,11]. The link between ROS and Toll induction was supported by provision of
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