The Anolpheles gambiae salivary protein repertoire: toward a functional analysis and salivary antigen identification.

Mosquito salivary glands represent the last barrier that Plasmodium parasite has to overcome before infecting the vertebrate host. The saliva of hematophagous arthropods is known to contain several pharmacological activities that can affect both human physiology (i.e. hemostatic, inflammatory and immune responses) and pathogen transmission. As far as the mosquito is concerned very little is currently known regarding immuno-modulatory properties of mosquito saliva and its effect on the transmission of disease agents. We have recently assembled a catalogue including approximately 70 Anopheles gambiae putative secreted salivary proteins and a striking observation is that no function can be assigned to almost half of them. In order to proceed toward a functional analysis we started expression of recombinant salivary proteins and we are optimizing conditions to obtain efficient and reproducible silencing of salivary genes. These represent useful tools to investigate the possible effects of salivary gene products on host immune response, on parasite transmission and to test candidate receptors involved in sporozoite invasion. Moreover, comparative analysis of the salivary transcriptomes of different mosquito species highlighted that several salivary proteins or protein families are genus-specific, i.e. are found exclusively in Anopheles as compared to Aedes or Culex species. It has recently been suggested that human immune response to Anopheles saliva may be useful as epidemiological marker of exposure to mosquito bites. In this respect the identification of immunogenic, Anopheles-specific, salivary antigens would allow to overcome cross-reactivity problems facilitating the use of salivary proteins in malaria epidemiological studies.