Borrelia miyamotoi infection is an emerging tick-borne disease that causes hard tick-borne relapsing fever. B. miyamotoi is transmitted through the bite of ticks, including Ixodes persulcatus. Although accumulating evidence suggests that tick salivary proteins enhance the infectivity of other tick-borne pathogens, the association of B. miyamotoi with tick-derived proteins remains unknown. In this study, the effect of I. persulcatus sialostatin L2 (Ip-sL2), a tick-derived cystatin, on specific immunity to B. miyamotoi was preliminarily investigated in vitro. Mice were immunized with heat-killed B. miyamotoi and in vitro analyses of the splenocytes of the immunized mice indicated that the expression levels of the activation markers of CD11c