Cloning and Expression of Gene Coding Cathepsin L of Rhipicephalus annulatus

BACKGROUND: Ticks are one of the most important ectoparasites in animals that cause economic losses in livestock industry. So, removal or reduction of ticks on animals is necessary. Cysteine proteases are among the compounds that play an important role in the physiological action of ticks and are a good candidate for the anti-tick vaccine. Cathepsins is one of the most important cysteine proteases. OBJECTIVES: The aim of this study was cloning and expression of recombinant cathepsin L gene of Rhipicephalus annulatus in order to evaluate its immunogenicity. METHODS: After collection the ticks were cultivated. Then RNA was extracted from ticks, cDNA was synthesized by using specific primer of cathepsin and amplification by RT-PCR. The desired genes were cloned into expressional pQE30 plasmid. Further, a shorter sequence of the cathepsin gene (654 bp) was prepared as a synthetic plasmid. The expression of the protein produced by both recombinant plasmids in the E.coliBL21 prokaryotic expression system is carried out and the immunity of the recombinant proteins was evaluated by Dot Blot and Western Blot using serum of challenged rabbits with recombinant protein and calves infected with ticks were examined and compared. RESULTS: The results of this study indicate that the protein derived from recombinant plasmid No. 2 had higher expression and purity due to its solubility. Also, the challenge of rabbit serum with these proteins was able to identify both recombinant proteins. But the serum of challenged calves with ticks did not show a satisfactory response with recombinant proteins. CONCLUSIONS: Although the sera reaction of calves infested with ticks was lower than the challenged rabbits sera with cathepsin L, this result was expected, because L cathepsin protein is considered as a concealed antigen.  Overall, the recombinant cathepsin L could be an appropriate candidate for immunizing calves against Rhipicephalus annulatus, although it seems further investigations are necessary.