Functional characterization and target validation of Amblyomma americanum serpin: AAS8

Ticks represent one of the most significant vectors of disease pathogens, and have a unique biology of prolonged attachment and feeding on their host. In the United States, Amblyomma americanum is among the most important of these tick vectors. In order to successfully feed, ticks inject a cocktail of proteins which facilitate feeding site maintenance, eluding the host defenses, and blood acquisition. Among the proteins injected into the host are serine protease inhibitors (serpins), hypothesized to play a role in thwarting the host immune system. One member of this family, AAS8, has previously been shown to be present in salivary gland tissue and to be immunogenic in rabbit hosts. Further expression analyses show this protein may be important in the midgut throughout the feeding process, and elsewhere in the tick at the 72h feeding time point. This protein may be involved in subduing host inflammation as substrate hydrolysis assays of recombinant AAS8 show high activity against serine protease cathepsin-G. The effect on tick feeding success of AAS8 and two closely related serpins, AAS 9 and 10, will be assessed by RNAi silencing.