Immunization effect of recombinant P27/30 protein expressed in Escherichia coli against the hard tick Haemaphysalis longicornis (Acari: Ixodidae) in rabbits

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

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.

Molecular cloning, expression and impact of ribosomal protein S-27 silencing in Haemaphysalis longicornis (Acari: Ixodidae)

Ticks, obligatory blood-feeding arthropods, are a major pathogen vector in humans and animals worldwide. Anti-tick vaccines are an exciting alternative to chemical acaricides for controlling these disease-transmitting vectors. However, identification of protective antigens for anti-tick vaccine development is challenging. Different ribosomal proteins play multifunctional roles in tick survival and feeding. Here, we first report the cloning and molecular characterization of ribosomal protein S27 (RPS-27) from the hard tick Haemaphysalis longicornis. We identified a complete open reading frame (ORF) of RPS-27: a 255-bp (base pair) cDNA encoding a mature protein of 84 amino-acid residues with a 9.4-kDa predicted molecular mass. Amino-acid sequence analysis revealed that RPS-27 was highly conserved among different tick and vertebrate animals with identity ranges of 97-98% and 60-85%, respectively. Phylogenetic tree analysis showed that RPS-27 from different tick species clustered together. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the RPS-27 mRNA transcript was expressed in all life stages. At the tissue level, it was more highly expressed in the salivary gland than in the midgut for both the fed and unfed conditions, which indicates a role for RPS-27 in tick feeding. In vitro analysis showed that recombinant RPS-27 (10-RPS-27) was successfully expressed in a pGEMEX-2 vector with an estimated 45-kDa molecular mass. The functional importance of RPS-27 was determined by gene silencing through RNA interference (RNAi). RPS-27 silencing showed a significant (P < 0.05) reduction of feeding abilityand engorgement weight after the blood meal in both nymph and adult female ticks and also significantly (P < 0.05) reduced molting rate in nymph. In addition, RPS-27 silencing in eggs led to abnormalities in shape and hatching. Taken together, our results suggest that RPS-27 is an important molecule that plays multiple roles in the tick life cycle including in both feeding and reproduction. Therefore, RPS-27 is an exciting target for future tick control strategies.

Identification of the tropomyosin (HL-Tm) in Haemaphysalis longicornis

Haemaphysalis longicornis tropomyosin (HL-Tm) was amplified by RT-PCR. The cDNA contained a 825 bp open reading frame coding for 274 amino acids with a predicted theoretical isoelectric point (pI) of 4.55 and molecular weight of 31.7 kDa. Real-time RT-PCR analysis showed that the expression levels of the HL-Tm in the unfed-females were significantly higher than in other tested developmental stages (eggs, unfed-larvae and unfed-nymphs). Western blot analysis showed that rabbit anti-serum against H. longicornis unfed-adult ticks recognized the recombinant HL-Tm protein (rHL-Tm). Immunization of rabbits with the rHL-Tm resulted in a statistically significant reduction of female engorgement and oviposition. Silencing of HL-Tm by RNAi showed a decrease in tick engorgement and oviposition, which is consistent with the effect of recombinant protein vaccine on the adults. These results showed that tick HL-Tm might be involved in the regulation of ticks blood-feeding, growth and oviposition.

Identification of salivary antigenic markers discriminating host exposition between two European ticks: Rhipicephalus sanguineus and Dermacentor reticulatus

To succeed blood meal, ticks inject salivary proteins to mammalian hosts, eliciting an antibody response against these foreign antigens. Although this immune response has been proposed as a surrogate marker of exposure to tick bites, identification of the corresponding antigens remains elusive. For this aim, a comparison by immunoblots of the kinetic IgG responses to protein salivary gland extracts from two European tick species, Rhipicephalus sanguineus or Dermacentor reticulatus, in rabbits was performed. A singularity in the immune patterns was observed according to rabbit exposure status and depending on the antigen source. Six and five bands were found specifically associated to R. sanguineus and to D. reticulatus exposures, respectively. The identity of these salivary antigenic proteins was determined using an original immunoproteomic approach. The utilization of these tick salivary proteins as biomarker candidates to discriminate R. sanguineus and/or D. reticulatus tick exposure or to develop anti-tick vaccines is discussed.

Characterization and evaluation of a Sarcoptes scabiei allergen as a candidate vaccine

Background

Sarcoptic mange caused by the mite Sarcoptes scabiei is a worldwide disease affecting both humans and animals. Here we report the molecular characterization and evaluation of a recombinant S. scabiei tropomyosin (SsTm) protein in a vaccination trial in rabbits.

Methods

The full-length cDNA was cloned in a bacterial pET vector, and the recombinant protein was expressed in BL21 (DE3) cells and purified. Using specific rabbit antiserum, tropomyosin was localized immunohistochemically in mite tissue sections. Vaccination trials with the recombiant SsTm was carried out in New Zealand rabbits.

Results

The full-length open reading frame (ORF) of the 852 bp cloned gene from S. scabiei encodes a 32.9 kDa protein. The amino acid sequence showed 98.94%, 97.89% and 98.59% homology to Dermatophagoides farina and Dermatophagoides pteronyssinus group 10 allergens and Psoroptes ovis tropomyosin, respectively. Tropomyosin was localized immunohistochemically in mite tissue sections mainly in the mouthparts, legs and integument of the epidermis. The predicted cross-reactivity of SsTm indicated that it is an allergenic protein. While vaccination with the recombiant SsTm resulted in high levels of specific IgG (P < 0.01), a low IgE antibody response and no significant protection against S. scabiei challenge were observed. After challenge, specific IgG levels remained significantly higher than the control (P < 0.01), while changes of total IgE levels were not significant (P > 0.05). However, the lesion areas in the vaccination group decreased at the end of the experiment compared with controls.

Conclusions

Although vaccination with recombinant SsTm did not efficiently control sarcoptic mange in rabbits, the immunogenic properties of tropomyosin suggest it may be developed as a vaccine with alternative adjuvants or delivery methods.

Molecular characterization of a myosin alkali light chain-like protein, a "concealed" antigen from the hard tick Haemaphysalis qinghaiensis

There should be some differences between antibodies generated by feeding ticks on animals and those derived by immunizing animals with tick extracts. Here, we found serum collected from sheep immunized with Haemaphysalis qinghaiensis salivary gland extracts could detect two more protein bands with molecular weights of 22 and 37 kDa (P22 and P37) on Western blots of extracts of tick salivary glands than serum from tick infected animals. Rabbit anti-H. qinghaiensis differential protein immune serum was then generated from P22 and P37 and was used to immunoscreen a cDNA library constructed from salivary glands, Malpighian tubules and ovaries of partially engorged H. qinghaiensis. A cDNA contains an open reading frame of 483 bp that codes for 160 amino acid residues with a coding capacity of 18 kDa was cloned and designated Hq02. Expression analysis by RT-PCR showed that this gene is expressed in salivary glands, midguts, other organs and different developmental stages of H. qinghaiensis. The predicted amino acid sequence of the Hq02 gene had high homology to some known myosin alkali light chain (MLC) proteins. A fusion protein consisting of 130 amino acids of Hq02 protein and 335 amino acids of T7 gene 10 protein was expressed in Escherichia coli and used to immunize sheep. Western blot showed that only rabbit anti-H. qinghaiensis differential protein immune serum could recognize the expressed Hq02 protein, while rabbit anti-H. qinghaiensis saliva immune could not. This proved Hq02 protein was a "concealed" antigen. Immunization with the recombinant Hq02 conferred a 21.8% reduction of engorgement weight for adult female ticks that fed on the immunized sheep. This is the first report of tick myosin alkali light chain and the function of this protein is discussed.

A house dust mite allergen homologue from poultry red mite Dermanyssus gallinae (De Geer)*

Tropomyosin is an allergenic, actin-binding protein and a proposed vaccine candidate from several species of parasite. Tropomyosin cDNA, obtained by polymerase chain reaction (PCR) amplification from Dermanyssus gallinae RNA, encoded a predicted protein with 89% and 88% identity to tropomyosins from the ticks Boophilus microplus and Haemaphysalis longicornis, respectively, and 85% identity to the house dust mite (HDM) tropomyosin Der p 10. Mouse antibodies raised against HDM tropomyosin reacted with a band of 38 kDa on Western blots of D. gallinae extract, consistent with the molecular masses of acarine tropomyosins and the putative product of the cDNA encoding D. gallinae tropomyosin. When the same preparation of D. gallinae proteins was used in Western blots with serum from infested hens, the IgY component of the serum bound to a number of mite proteins, but not to tropomyosin, indicating that hens are not directly exposed to this allergen during a natural infestation. Immunolocalization of tropomyosin in mites indicated a ubiquitous distribution of the molecule in mite tissues. Immunolocalization and Western blotting also indicated that poultry red mites ingest host IgY.