Wolbachia surface protein induces innate immune responses in mosquito cells

Background: Wolbachia endosymbiotic bacteria are capable of inducing chronic upregulation of insect immune genes in some situations and this phenotype may influence the transmission of important insect borne pathogens. However the molecules involved in these interactions have not been characterized. Results: Here we show that recombinant Wolbachia Surface Protein (WSP) stimulates increased transcription of immune genes in mosquito cells derived from the mosquito Anopheles gambiae, which is naturally uninfected with Wolbachia; at least two of the upregulated genes, TEP1 and APL1, are known to be important in Plasmodium killing in this species. When cells from Aedes albopictus, which is naturally Wolbachia-infected, were challenged with WSP lower levels of upregulation were observed than for the An. gambiae cells. Conclusions: We have found that WSP is a strong immune elicitor in a naturally Wolbachia-uninfected mosquito species (Anopheles gambiae) while a milder elicitor in a naturally-infected species (Aedes albopictus). Since the WSP of a mosquito non-native (nematode) Wolbachia strain was used, these data suggest that there is a generalized tolerance to WSP in Ae. albopictus.