Evaluation of immune protection induced by DNA vaccines from Haemaphysalis longicornis paramyosin in rabbits

Abstract

Background: Haemaphysalis longicornis is a blood-sucking ectoparasite that can cause diseases by transmitting some pathogens to humans and animals. Paramyosin (Pmy) is an immunomodulatory protein, which plays an important role in immune reactions against parasites. In this study, we evaluated the immune protection elicited by recombinant plasmids encoding H. longicornis Pmy in rabbits.

Results: Rabbits vaccinated with pcDNA3.1(+)-Pmy developed high level of IgG compared to control group, suggesting that humoral immune response was induced by vaccination. On the fourth day after fed on the rabbit, some female adults died and the mortality rate from pcDNA3.1(+)-Pmy group (27.31%) was significantly higher than that of the control group (P < 0.0001). Other female ticks were attached to the rabbits until detachment, and the average engorgement weight, oviposition of female adult from pcDNA3.1(+)-Pmy group were 109.61 ± 4.24 mg and 48.39 ± 4.06 mg, respectively, which correspondingly resulted in 36 and 39% reduction compared with that of the control group (P < 0.0001). In brief, vaccination with Pmy plasmid DNA provided an overall efficacy of 50% in immune protection of rabbits.

Conclusions: This study suggested that Pmy DNA vaccine can induce effective humoral immune response and partially protected rabbit against H. longicornis infection.

Keywords: DNA vaccine; Haemaphysalis longicornis; Immune protection; Pmy.

Fig. 1

Antibody responses from immunized rabbits with DNA vaccine. Sera (2/group) were collected every seven days and determined by ELISA. The experiment was repeated three times. Results are shown as means ± SEM, and statistically significant differences are indicated by asterisks (*P < 0.05). The arrows indicate the days of the initial vaccination and the two boosters

Fig. 2

Different biological parameters of female ticks from rabbits tests. a Average mortality of female adults. b Average engorgement weight of female adults. c Average ovipositions of female adults. d Average hatchability. In total, 240 female adult ticks (n = 240) in Fig. 2a were used in each group, while biting ticks (n = 202 or 174) in Fig. 2b-d were used in control group and pcDNA3.1(+)-Pmy group, respectively. Results are shown as means ± SEM and statistically significant differences are indicated by asterisks (*P < 0.05)

Fig. 3

Comparison of tick size between two groups. a Control group (body width: 7.00 ± 0.38 mm), b Immunization group with pcDNA3.1(+)-Pmy (body width: 4.83 ± 0.23 mm). Female ticks were attached to immunized rabbits for blood-feeding until complete engorgement. Results are shown as means ± SEM