Hemalin vaccination modulates the host immune response and reproductive cycle of Haemaphysalis longicornis

Hejia Ma; Jingkai Ai; Yansha La; Xinyuan Zhao; Ankang Zeng; Qi Qin; Shangjiali Feng; Ming Kang; Yali Sun; Jixu Li

doi:10.1016/j.vetpar.2023.110051

Hemalin vaccination modulates the host immune response and reproductive cycle of Haemaphysalis longicornis

Vet Parasitol. 2023 Oct 10:323:110051. doi: 10.1016/j.vetpar.2023.110051. Online ahead of print.

Authors

Hejia Ma¹, Jingkai Ai¹, Yansha La¹, Xinyuan Zhao¹, Ankang Zeng¹, Qi Qin¹, Shangjiali Feng¹, Ming Kang¹, Yali Sun², Jixu Li³

Affiliations

¹ State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining 810016, China; College of Agriculture and Animal Husbandry, Qinghai University, Xining 810016, China.
² State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining 810016, China; College of Agriculture and Animal Husbandry, Qinghai University, Xining 810016, China; Qinghai Provincial Key Laboratory of Pathogen Diagnosis for Animal Diseases and Green Technical Research for Prevention and Control, Qinghai University, Xining 810016, China.
³ State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining 810016, China; College of Agriculture and Animal Husbandry, Qinghai University, Xining 810016, China; Qinghai Provincial Key Laboratory of Pathogen Diagnosis for Animal Diseases and Green Technical Research for Prevention and Control, Qinghai University, Xining 810016, China. Electronic address: lijixu@qhu.edu.cn.

PMID: 37866015
DOI: 10.1016/j.vetpar.2023.110051

Abstract

Haemaphysalis longicornis can transmit high varieties of tick-borne pathogens (TBPs), and a primary strategy for preventing the transmission of those TBPs is to control ticks. Hemalin, a thrombin inhibitor of the Kunitz-type family and a crucial component in H. longicornis feeding process has been isolated from parthenogentic ticks. This study aimed to evaluate the validity of a recombinant Hemalin (rHlHemalin) vaccination as an anti-tick vaccine against H. longicornis in rabbits to find a new candidate for an effective tick control. In this study, mouse splenocytes were isolated and used to investigate immune responses after rHlHemalin stimulation. The rabbits were vaccinated with the rHlHemalin protein. After tick challenges, body weight at engorgement, egg mass, and the reproductive cycle of H. longicornis were evaluated. To confirm the vaccination, the passive immunization tests of α-rHlHemalin sera were performed. The results showed that the rHlHemalin protein could stimulate cytokine production in mouse splenocytes. Vaccination assay revealed that the periods from tick infestations to egg-hatch in the vaccination group were significantly longer than those in the phosphate buffer saline (PBS) group (P = 0.0003). In addition, the tick body weight at engorgement (P = 0.0019) and egg mass at 10 days after oviposition (P = 0.0232) were higher than those in the PBS group. These findings were consistent with the current passive immunization results and suggest rHlHemalin vaccination extended the reproductive cycle in H. longicornis but did not decrease the body weight at engorgement or weight of egg mass. Therefore, it is debatable whether Hemalin vaccination is highly-effective anti-tick vaccine or not. However, due to the importance of thrombin inhibitors in tick blood feeding and blood digestion, additional inhibitor-based vaccines should be developed aiming to find an effective and environmentally friendly biological strategy to combat ticks.

Keywords: Anti-tick vaccine; Asian longhorned ticks; Immunity; RHlHemalin; Tick reproduction.