ORIGINAL PAPER Cloning and characterization of a cDNA clone encoding calreticulin from Haemaphysalis qinghaiensis (Acari: Ixodidae) Jinliang Gao & Jianxun Luo & Ruiquan Fan & Volker Fingerle & Guiquan Guan & Zhijie Liu & Youquan Li & Haiping Zhao & Miling Ma & Junlong Liu & Aihong Liu & Qiaoyun Ren & Zhisheng Dang & Chihiro Sugimoto & Hong Yin Received: 30 August 2007 / Accepted: 23 November 2007 / Published online: 18 December 2007 # Springer-Verlag 2007 Abstract The application of anti-tick vaccine has been shown to be the most promising alternative strategy compared to the current use of acaricides that suffer from a number of serious limitations. The success of this method is dependent upon identification and cloning of potential tick vaccine antigens. Previously, we have cloned 21 positive clones (named from Hq02 to Hq22) by immunoscreening complimentary DNA (cDNA) libraries of Haemaphysalis qinghaiensis; however, some of those clones did not contain open reading frames (ORF). In this study, we amplified the entire sequence of Hq07 by using rapid amplification of the cDNA ends. Hq07 contains an ORF of 1,233 bp that encodes for 410 amino acid residues with a coding capacity of 47 kDa. Search of the cloned sequences against GenBank revealed that Hq07 is a calreticulin (CRT)-similar clone and designated HqCRT. Expression analysis by reverse transcription– polymerase chain reaction showed that this gene is ubiqui- tously expressed at different developmental stages and in different tissues of H. qinghaiensis. The gene was expressed as glutathione S-transferase-fused proteins in a prokaryotic system. Western blot analysis revealed that native HqCRT was secreted into their hosts by ticks during blood sucking. Vaccination of sheep with rHqCRT conferred protective immunity against ticks, resulting in 54.3% mortality in adult ticks, compared to the 38.7% death rate in the control group. These results demonstrated that rHqCRT might be a useful vaccine candidate antigen for biological control of H. qinghaiensis. Introduction Ticks are not only important vectors of human diseases but also the most important arthropods transmitting pathogens to domestic animals, causing economic losses for animal husbandry (Sonenshine 1991). Haemaphysalis qinghaiensis, a distinctive tick species of China, is a three-host tick and a vector of Theileria sp. and Babesia sp. for small ruminants. It also transmits Theileria sinense, which can infect yaks (Guan et al. 2002; Yin et al. 2002a, b, c; Yin et al. 2004). H. qinghaiensis and the protozoal diseases it transmits are a major economic burden to animal husbandry in China. The use of chemical acaricides is, at present, the major tick control strategy that is widely available. However, this approach is problematic because of the chemical pollution of the environment (Willadsen and Kemp 1988) and the potential for ticks to develop resistance against acaricides, reducing their effectiveness (Riding et al. 1994). These limitations have necessitated the search for alternative tick control measures. A series of studies (Tellam et al. 1992; Rand et al. 1989; Willadsen et al. 1989) carried out by an Australian group have led to the commercialization of the first ever Parasitol Res (2008) 102:737–746 DOI 10.1007/s00436-007-0826-y J. Gao : J. Luo : R. Fan : G. Guan : Z. Liu : Y. Li : H. Zhao : M. Ma : J. Liu : A. Liu : Q. Ren : Z. Dang : H. Yin (*) Key Laboratory of Veterinary Parasitology of Gansu Province, State Key Laboratory of Veterinary Etiological Biology, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou 730046, China e-mail: yinhong@public.lz.gs.cn J. Gao : V. Fingerle Max von Pettenkofer-Institut für Medizinische Mikrobiologie und Hygiene der Ludwig-Maximilians-Universität München, 80336 Munich, Germany C. Sugimoto The National Research Center for Protozoan Disease, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan