Development of a Vaccine Against Boophilus spp.

Ticks are important vectors of pathogens that infect humans and domestic animals. Transmission of selected pathogens has been shown to be enhanced by tick saliva, which contains several bioactive components. Recently, a unique phospholipase A₂ (PLA₂) was identified by our laboratory in saliva from the Lone Star tick, Amblyomma americanum, which vectors human granulotcytic Ehrlichia (HGE) and the American dog tick, Dermacentor variabilis, the vector of the ehrlichial bovine pathogen Anaplasma marginale. Previous research has demonstrated that PLA₂ plays a direct role in the ability of several intracellular rickettsiae and protozoans to invade host cells.  We hypothesize that this unique tick PLA₂ may be a key factor in tick saliva that facilitates transmission of ehrlichial tick-borne pathogens. We proposed to isolate and characterize the gene(s) for the tick salivary gland ts-PLA₂. We have used the A. marginale/ tick cell culture system, recently developed in our laboratory, as a model system to show that the bee venom PLA₂ and the D. variabilis saliva enhance the infection of tick cells by an ehrlichial pathogen. The system developed offers the possibility to test whether the putative enhancement can be blocked using PLA₂ inhibitors specific for the ts-PLA₂ and antibodies against the recombinant enzyme. A construction of an expression tick cDNA library is in progress to screen for the ts-PLA₂ activity to isolate the genes encoding for this enzyme. Experiments are planned to characterize the ability of recombinant ts-PLA₂ to enhance the infection of A. marginale in the tick cell culture system and to conduct similar experiments on HGE and E. chaffeensis which can also be propagated in the tick cell line.