Characterization of a concealed antigen Hq05 from the hard tick Haemaphysalis qinghaiensis and its effect as a vaccine against tick infestation in sheep

Positive clone Hq05 of Haemaphysalis qinghaiensis (named following those cDNA clones cloned from the tick before) was obtained by differentially screening of a cDNA library of the tick with rabbit anti-tick salivary gland serum and rabbit anti-tick saliva serum. Hq05 contains an open reading frame (ORF) of 540 bp that codes for 179 amino acid residues with a coding capacity of 20 kDa. Sequence similarity and phylogenetic analyses indicated that Hq05 was a novel gene. Expression analysis by reverse transcription-polymerase chain reaction indicated that the gene was expressed in nymphal and adult stage of H. qinghaiensis tick and its salivary glands, but not in midguts. The cDNA was expressed as glutathione S-transferase (GST)-fused protein in a procariotic system. Western blot showed that only rabbit anti-H. qinghaiensis salivary gland serum could recognize the expressed GST-Hq05 (46 kDa) protein, while both rabbit negative serum and rabbit anti-H. qinghaiensis saliva serum could not react with the expressed protein. This proved the recombinant protein was a “concealed” antigen of H. qinghaiensis. Vaccination of sheep with rHq05 conferred a significant protective immunity in sheep, resulting in a 40% reduction of the amount of eggs laid by each tick and the hatching capability of eggs decreased by 37% compared to the controls. These results showed that rHq05 could be a candidate tick vaccine molecule for the control of H. qinghaiensis.