Ixodes scapularis tick saliva serine protease inhibitors (serpins): Roles in tick feeding regulation

Ixodes scapularis is arguably the most medically important tick species in the United States. This tick transmits 5 of the 14 human tick borne disease (TBD) agents in the USA: Borrelia burgdoferri, Anaplasma phagocytophilum, B. miyamotoi, Babesia microti, and Powassan virus. It is hypothesized that ticks inject serine protease inhibitors (serpins) into their host during feeding to overcome the host’s defense mechanisms. This study characterizes a blood meal responsive I. scapularis serpin, in house referred to as serpin 27A. We demonstrate that Pichia pastoris-expressed recombinant serpin 27A bound antibodies to I. scapularis tick saliva proteins indicating that the native form of this protein is injected into the host during tick feeding. This serpin may play a role in decreasing host inflammation as substrate hydrolysis assays indicate high activity against cathepsin-G and elastase.