Babesial Vector Tick Defensin againstBabesiasp. Parasites

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Abstract
Antimicrobial peptides are major components of host innate immunity, a well-conserved, evolutionarily ancient defensive mechanism. Infectious disease-bearing vector ticks are thought to possess specific defense molecules against the transmitted pathogens that have been acquired during their evolution. We found in the tickHaemaphysalis longicornisa novel parasiticidal peptide named longicin that may have evolved from a common ancestral peptide resembling spider and scorpion toxins.H. longicornisis the primary vector forBabesiasp. parasites in Japan. Longicin also displayed bactericidal and fungicidal properties that resemble those of defensin homologues from invertebrates and vertebrates. Longicin showed a remarkable ability to inhibit the proliferation of merozoites, an erythrocyte blood stage of equineBabesia equi, by killing the parasites. Longicin was localized at the surface of theBabesiasp. parasites, as demonstrated by confocal microscopic analysis. In an in vivo experiment, longicin induced significant reduction of parasitemia in animals infected with the zoonotic and murineB. microti. Moreover, RNA interference data demonstrated that endogenous longicin is able to directly kill the canineB. gibsoni, thus indicating that it may play a role in regulating the vectorial capacity in the vector tickH. longicornis. Theoretically, longicin may serve as a model for the development of chemotherapeutic compounds against tick-borne disease organisms.