Molecular characterization of a Haemaphysalis longicornis tick salivary gland-associated 29-kilodalton protein and its effect as a vaccine against tick infestation in rabbits

The use of tick vaccines in mammalian hosts has been shown to be the most p romising alternative tick control method to current use of acaricides, whic h suffers from a number of limitations. However, the success of this method is dependent on the identification, cloning, and in vitro expression of ti ck molecules involved in the mediation of key physiological roles with resp ect to the biological success of a tick as a vector and pest. We have seque nced and characterized a Haemaphysalis longicornis tick salivary gland-asso ciated cDNA coding for a 29-kDa extracellular matrix-like protein. This pro tein is expressed in both unfed and fed immature and mature H. longicornis ticks. The predicted amino acid sequence of p29 shows high homology to sequ ences of some known extracellular matrix like-proteins with the structural conservation similar to all known collagen proteins. Immunization with the recombinant p29 conferred a significant protective immunity in rabbits, res ulting in reduced engorgement weight for adult ticks and up to 40 and 56% m ortality in larvae and nymphs that fed on the immunized rabbits. We specula te that this protein is associated with formation of tick cement, a chemica l compound that enables the tick to remain attached to the host, and sugges t a role for p29 as a candidate tick vaccine molecule for the control of ti cks. We have discussed our findings with respect to the search of tick mole cules for vaccine candidates.