Immunological properties of engineered Asaia symbionts: implications for the control of mosquito-borne diseases

The genus Wolbachia collects intracellular bacteria, which commonly infect arthropods. It is well-known that Wolbachia is capable of inducing the production of reactive oxygen species and innate immune effectors in mosquitoes; this immune stimulation is likely involved in the reduction of arthropod vector capacity, toward a variety of pathogens. In fact, the presence of Wolbachia has been associated with the inhibition of virus and parasites development in arthropods. Among Wolbachia molecules, the Wolbachia surface protein (WSP) has been shown to induce immune responses in mosquito cell lines, and Th1 polarization in mammalian hosts, after stimulation of innate-immunity receptors. Due to the intrinsic features of Wolbachia bacterium e.g. not culturable in cell-free media, its use in vector-borne diseases control is limited; for this reason we realized a chimeric bacterium of the genus Asaia, symbiont of Diptera vectors, to express WSP protein. The immunological effects of this engineered bacterium have been tested evaluating the stimulation of the innate immune response in mosquito cell lines and in vivo in presence of Asaia producing WSP. Investigations on the immunological properties of WSP in mosquitoes could generate novel insights into the insect-bacterium relationships, thus providing novel ideas toward the development of tools for the control of mosquito-borne diseases.