Vaccination Effects of Recombinant Chitinase Protein from the Hard Tick Haemaphysalis longicornis (Acari: Ixodidae)

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The success of immunological method for the control of ticks depend on the use of potential key antigens as tick vaccine candidates. Chitinase is induced by ecdysteroids to degrade the older chitin at the time of molting. Previously, we cloned a gene encoding 113 kDa protein (CHT1) of Haemaphysalis longicornis, and identified the CHT1 as a protein of chitinase (You et al. 2003). In this study, the recombinant CHT1 (rCHT1) expressed in Escherichia coli was used to immunize mice. The mice were challenge-infested with ticks at different developmental stages of the same species. The rCHT1 stimulated a specific protective anti-tick immune response in the mice as evidenced by the significant longer feeding periods in the larval ticks and significant difference in the egg weights. The molting periods in the ticks fed on the rCHT1-immunized mice tended to be longer than those of the controls. Nymphal ticks fed on the rCHT1-immunized mice showed lower molting rate (76.7%) compared to 96.7% for the control. These results demonstrated that the rCHT1-immunized mice sera implicated on molting step, suggesting that the rCHT1 might be a useful vaccine candidate antigen for biological control of the tick.