A mosquito salivary protein facilitates sporozoite traversal of host cells.

Malaria begins when Plasmodium-infected Anopheles mosquitoes take a blood meal on a vertebrate. During the initial probing process, mosquitoes inject saliva and sporozoites into the host skin. Components of mosquito saliva have the potential to influence sporozoite functionality. Sporozoite-associated mosquito saliva protein 1 (SAMSP1, AGAP013726) was among several proteins identified when sporozoites were isolated from saliva, suggesting it may have an effect on Plasmodium. Recombinant SAMSP1 enhanced sporozoite gliding and cell traversal activity in vitro. Moreover, SAMSP1 decreased neutrophil chemotaxis in vivo and in vitro, thereby also exerting an influence on the host environment in which the sporozoites reside. Active or passive immunization of mice with SAMSP1 or SAMSP1 antisera diminished the initial Plasmodium burden following infection. Passive immunization of mice with SAMSP1 antisera also added to the protective effect of a circumsporozoite protein (CSP) monoclonal antibody. SAMSP1 is, therefore, a mosquito saliva protein that can influence sporozoite infectivity in the vertebrate host.