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Babesial Vector Tick Defensin against Babesia sp. Parasites ^,

Laboratory of Parasitic Diseases, National Institute of Animal Health, National Agricultural and Food Research Organization, Tsukuba, Ibaraki 305-0856, Japan,¹ National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-0834, Japan,² Institute of Arthropodology and Parasitology, Georgia Southern University, Statesboro, Georgia,³ Department of Emerging Infectious Diseases, School of Veterinary Medicine, Kagoshima University, Korimoto, Kagoshima 890-0065, Japan⁴

Received 15 February 2007/ Returned for modification 17 March 2007/ Accepted 26 April 2007

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 tick Haemaphysalis longicornis a novel parasiticidal peptide named longicin that may have evolved from a common ancestral peptide resembling spider and scorpion toxins. H. longicornis is the primary vector for Babesia sp. 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 equine Babesia equi, by killing the parasites. Longicin was localized at the surface of the Babesia sp. 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 murine B. microti. Moreover, RNA interference data demonstrated that endogenous longicin is able to directly kill the canine B. gibsoni, thus indicating that it may play a role in regulating the vectorial capacity in the vector tick H. longicornis. Theoretically, longicin may serve as a model for the development of chemotherapeutic compounds against tick-borne disease organisms.

Published ahead of print on 7 May 2007.

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Editor: W. A. Petri, Jr.