Constituting a glutathione S-transferase-cocktail vaccine against tick infestation

In vitro identification of neutralizing epitopes of Rhipicephalus microplus serpin 17 (RmS-17)

BACKGROUND

Rhipicephalus microplus poses a significant problem for livestock worldwide and is primarily controlled with synthetic acaricides. The continuous use of acaricides results in the selection of resistance and causes environmental harm. Vaccination presents an alternative solution to this problem, although searching for the suitable antigen is still a work in progress. Salivary proteins hold promise for inclusion in vaccine formulation due to their roles in modulating host responses, assisting blood feeding and pathogen transmission. Serpins are a class of proteinase inhibitors and are among the molecules found in tick saliva that modulate host blood coagulation, inflammation, and adaptive immune responses. Previous studies have demonstrated the potential of R. microplus serpin 17 (RmS-17) to interfere with the host's defenses, and antibodies have been shown to neutralize its effects. This makes RmS-17 an putative target for vaccine development.

METHODS

Epitope mapping of RmS-17 was achieved using in silico approach combining linear B-cell epitope and antigenicity predictor. In addition, epitope mapping using overlapping peptides in an ELISA screening was used. The serpin tridimensional structure and the epitopes spatial location within the molecule were determined. Peptides were synthetized based on the predictions and used for the production of rabbit anti-sera. Purified IgG's were used to assess the antibodies capacity to neutralize RmS-17.

RESULTS

Through in silico mapping, nine potential B cell epitope regions were screened, with p1RmS-17 and p2RmS-17 selected for the experiment based on antigen prediction. In the ELISA screening using overlapping peptides, eight antibody-binding regions were identified, and p3RmS-17 and p4RmS-17 were chosen. Antibodies raised against p3RmS-17 and p4RmS-17 partially neutralized RmS-17 activity.

CONCLUSION

It was found that antibodies against a single epitope are sufficient to partially neutralize RmS-17 activity. These findings support the possibility of using an epitope-based vaccine for immunization against R. microplus.

Immunologic characterization of the Bm05br protein using the Rhipicephalus linnaei (Audouin, 1826) species as a tick model

The identification and characterization of tick proteins allow us to discover new physiological targets useful for the development of tick control methods. Bm05br (Brazil Rhipicephalus microplus protein 05) is a protein with unknown function identified in the saliva of R. microplus. Rs05br (Brazil Rhipicephalus sanguineus protein 05), a protein with 99 % similarity to Bm05br, was identified in Rhipicephalus linnaei egg, larval, and nymphal stages, as well as in adult saliva. To improve the knowledge about both proteins, immunological characterization was performed, including antigenicity analysis, vaccination trials, and artificial feeding. The sequence and antigenicity analysis of Bm05br and Rs05br proteins showed that R. linnaei could serve as a tick model for cross-protection studies. The recombinant Bm05br protein was immunogenic. Anti-Bm05br antibodies recognized the homologous protein Rs05br in different stages, organs, and in the saliva of R. linnaei. Although rBm05br did not induce a protective response against infestation in R. linnaei in this study, further experiments could be developed taking into account new formulations and animal models for vaccination. These results also serve as a reference for future research on the function of these proteins in R. microplus and R. linnaei physiology, as well as other species of the genus Rhipicephalus.

In Vivo Characterization of the Anti-Glutathione S-Transferase Antibody Using an In Vitro Mite Feeding Model

Poultry red mites (Dermanyssus gallinae, PRMs), tropical fowl mites (Ornithonyssus bursa, TFMs), and northern fowl mites (O. sylviarum, NFMs) are blood-feeding pests that debilitate poultry worldwide. Glutathione S-transferase (GST) plays an important role in the detoxification and drug metabolism of mites. However, research on avian mite GSTs as vaccine antigens is still lacking. Therefore, we aimed to evaluate the potential of avian mite GSTs for vaccine development. We identified GST genes from TFMs and NFMs. We prepared recombinant GST (rGST) from TFMs, NFMs, and PRMs, and assessed their protein functions. Moreover, we evaluated the cross-reactivity and acaricidal effect of immune plasma against each rGST on TFMs, NFMs, and PRMs. The deduced amino acid sequences of GSTs from TFMs and NFMs were 80% similar to those of the PRMs. The rGSTs exhibited catalytic activity in conjugating glutathione to the 1-chloro-2,4-dinitrobenzene substrate. Immune plasma against each rGST showed cross-reactivity with rGST from different mite species. Moreover, the survival rate of PRMs fed with immune plasma against the rGST of TFMs and NFMs was significantly lower than that of the control plasma. These results demonstrate the potential application of GST as an antigen for the development of a broad-spectrum vaccine against avian mites.

Cross-species immunoprotective antigens (subolesin, ferritin 2 and P0) provide protection against Rhipicephalus sanguineus sensu lato

BACKGROUND

Tick control is mostly hampered by the rise of acaricide-resistant tick populations. Significant efforts have focused on developing alternative control methods, including cross-species protective and/or cocktail-based anti-tick vaccines, to achieve protection against various tick species.

METHODS

In this study, full-length open reading frames encoding subolesin (SUB) from Rhipicephalus microplus and ferritin 2 (FER2) from Hyalomma anatolicum as well as the partial 60S acidic ribosomal protein (P0) from R. microplus were cloned, expressed in Escherichia coli and used as vaccine antigens against Rhipicephalus sanguineus sensu lato (R. sanguineus s.l.) infestation in rabbits.

RESULTS

In silico analyses revealed that the SUB, P0 and FER2 proteins were antigenic and displayed limited similarity to the host's homologous proteins. The proteins shared identities of 97.5%, 100% and 89.5% with their SUB, P0 and FER2 R. sanguineus s.l. orthologous sequences, respectively. Antibodies against each recombinant protein cross-recognized the native proteins in the different tissues and developmental stages of R. sanguineus s.l. Overall efficacy of the SUB, FER2 and cocktail (SUB+FER2+P0) vaccines against R. sanguineus s.l. infestation was 86.3%, 95.9% and 90.9%, respectively.

CONCLUSIONS

Both mono-antigen and the cocktail anti-tick vaccines affected the biological parameters of R. sanguineus s.l. infestation in the rabbit model, which could be extrapolated to its infested host under natural conditions. These findings support the possibility of using mono-antigenic and cocktail-based vaccines for large-scale anti-tick vaccine development against multiple tick species.

Rabbits as Animal Models for Anti-Tick Vaccine Development: A Global Scenario

Studies evaluating candidate tick-derived proteins as anti-tick vaccines in natural hosts have been limited due to high costs. To overcome this problem, animal models are used in immunization tests. The aim of this article was to review the use of rabbits as an experimental model for the evaluation of tick-derived proteins as vaccines. A total of 57 tick proteins were tested for their immunogenic potential using rabbits as models for vaccination. The most commonly used rabbit breeds were New Zealand (73.8%), Japanese white (19%), Californians (4.8%) and Flemish lop-eared (2.4%) rabbits. Anti-tick vaccines efficacy resulted in up to 99.9%. Haemaphysalis longicornis (17.9%) and Ornithodoros moubata (12.8%) were the most common tick models in vaccination trials. Experiments with rabbits have revealed that some proteins (CoAQP, OeAQP, OeAQP1, Bm86, GST-Hl, 64TRP, serpins and voraxin) can induce immune responses against various tick species. In addition, in some cases it was possible to determine that the vaccine efficacy in rabbits was similar to that of experiments performed on natural hosts (e.g., Bm86, IrFER2, RmFER2, serpins and serine protease inhibitor). In conclusion, results showed that prior to performing anti-tick vaccination trials using natural hosts, rabbits can be used as suitable experimental models for these studies.

Egg protein profile and dynamics during embryogenesis in Haemaphysalis flava ticks

Tick eggs contain all essential proteins for embryogenesis, and egg proteins are a potential reservoir of tick-protective antigens. However, the protein profile and dynamics during embryonic development remain unknown. This study aimed to depict the protein profile and dynamics in tick embryogenesis, further providing protein candidates for targeted interventions. Eggs from Haemaphysalis flava ticks were incubated at 28 °C and 85% relative humidity. On days 0 (newly laid eggs without incubation), 7, 14 and 21, eggs were collected, dewaxed and subject to protein extraction. Extracted proteins were digested by filter-aided sample preparation and analyzed by liquid chromatography-tandem mass spectrometry (LC/MS-MS). MS data were searched against an in-house H. flava protein database for tick-derived protein identification. Abundances of 40 selected high-confidence proteins were further quantified by LC-parallel reaction monitoring (PRM)/MS analysis throughout egg incubation. A total of 93 high-confidence proteins were identified in eggs on 0-day incubation. Identified proteins belonged to seven functional categories: transporters, enzymes, proteinase inhibitors, immunity-related proteins, cytoskeletal proteins, heat shock proteins and uncharacterized proteins. The enzyme category contained the most types of proteins. Neutrophil elastase inhibitors represented the most abundant proteins in terms of intensity-based absolute-protein-quantification. LC-PRM/MS revealed that the abundances of 20 proteins increased including enolase, calreticulin, actin, GAPDH et cetera, and the abundances of 11 proteins decreased including vitellogenins, neutrophil elastase inhibitor, carboxypeptidase Q, et cetera from 0- to 21-day incubation. This study provides the most comprehensive egg protein profile and dynamics during tick embryogenesis. Further investigations are needed to test the tick-control efficacy by targeting the egg proteins.

Universal Tick Vaccines: Candidates and Remaining Challenges

Recent advancements in molecular biology, particularly regarding massively parallel sequencing technologies, have enabled scientists to gain more insight into the physiology of ticks. While there has been progress in identifying tick proteins and the pathways they are involved in, the specificities of tick-host interaction at the molecular level are not yet fully understood. Indeed, the development of effective commercial tick vaccines has been slower than expected. While omics studies have pointed to some potential vaccine immunogens, selecting suitable antigens for a multi-antigenic vaccine is very complex due to the participation of redundant molecules in biological pathways. The expansion of ticks and their pathogens into new territories and exposure to new hosts makes it necessary to evaluate vaccine efficacy in unusual and non-domestic host species. This situation makes ticks and tick-borne diseases an increasing threat to animal and human health globally, demanding an urgent availability of vaccines against multiple tick species and their pathogens. This review discusses the challenges and advancements in the search for universal tick vaccines, including promising new antigen candidates, and indicates future directions in this crucial research field.

Potential of ferritin 2 as an antigen for the development of a universal vaccine for avian mites, poultry red mites, tropical fowl mites, and northern fowl mites

Introduction

Poultry red mites (PRMs, Dermanyssus gallinae), blood-sucking ectoparasites, are a threat to the poultry industry because of reduced production caused by infestation. In addition, tropical fowl mites (TFMs, Ornithonyssus bursa) and northern fowl mites (NFMs, Ornithonyssus sylviarum) are hematophagous, distributed in various regions, genetically and morphologically close to PRMs, and cause similar problems to the poultry industry. Vaccine approaches have been studied for PRM control, and several molecules have been identified in PRMs as candidates for effective vaccine antigens. The development of an anti-PRM vaccine as a universal vaccine with broad efficacy against avian mites could improve the productivity of poultry farms worldwide. Molecules that are highly conserved among avian mites and have critical functions in the physiology and growth of mites could be ideal antigen candidates for the development of universal vaccines. Ferritin 2 (FER2), an iron-binding protein, is critical for the reproduction and survival of PRMs and has been reported as a useful vaccine antigen for the control of PRMs and a candidate for the universal vaccine antigen in some tick species.

Method and results

Herein, we identified and characterized FER2 in TFMs and NFM. Compared with the sequence of PRM, the ferroxidase centers of the heavy chain subunits were conserved in FER2 of TFMs and NFMs. Phylogenetic analysis revealed that FER2 belongs to clusters of secretory ferritins of mites and other arthropods. Recombinant FER2 (rFER2) proteins from PRMs, TFMs, and NFMs exhibited iron-binding abilities. Immunization with each rFER2 induced strong antibody responses in chickens, and each immune plasma cross-reacted with rFER2 from different mites. Moreover, mortality rates of PRMs fed with immune plasma against rFER2 from TFMs or NFMs, in addition to PRMs, were higher than those of control plasma.

Discussion

rFER2 from each avian mite exhibited anti-PRM effects. This data suggests that it has the potential to be used as an antigen candidate for a universal vaccine against avian mites. Further studies are needed to access the usefulness of FER2 as a universal vaccine for the control of avian mites.

The Correlation between Subolesin-Reactive Epitopes and Vaccine Efficacy

Vaccination is an environmentally-friendly alternative for tick control. The tick antigen Subolesin (SUB) has shown protection in vaccines for the control of multiple tick species in cattle. Additionally, recent approaches in quantum vaccinomics have predicted SUB-protective epitopes and the peptide sequences involved in protein−protein interactions in this tick antigen. Therefore, the identification of B-cell−reactive epitopes by epitope mapping using a SUB peptide array could be essential as a novel strategy for vaccine development. Subolesin can be used as a model to evaluate the effectiveness of these approaches for the identification of protective epitopes related to vaccine protection and efficacy. In this study, the mapping of B-cell linear epitopes of SUB from three different tick species common in Uganda (Rhipicephalus appendiculatus, R. decoloratus, and Amblyomma variegatum) was conducted using serum samples from two cattle breeds immunized with SUB-based vaccines. The results showed that in cattle immunized with SUB from R. appendiculatus (SUBra) all the reactive peptides (Z-score > 2) recognized by IgG were also significant (Z-ratio > 1.96) when compared to the control group. Additionally, some of the reactive peptides recognized by IgG from the control group were also recognized in SUB cocktail−immunized groups. As a significant result, cattle groups that showed the highest vaccine efficacy were Bos indicus immunized with a SUB cocktail (92%), and crossbred cattle were immunized with SUBra (90%) against R. appendiculatus ticks; the IgG from these groups recognized overlapping epitopes from the peptide SPTGLSPGLSPVRDQPLFTFRQVGLICERMMKERESQIRDEYDHVLSAKLAEQYDTFVKFTYDQKRFEGATPSYLS (Z-ratio > 1.96), which partially corresponded to a Q38 peptide and the SUB protein interaction domain. These identified epitopes could be related to the protection and efficacy of the SUB-based vaccines, and new chimeras containing these protective epitopes could be designed using this new approach.

Ticks and antibodies: May parasite density and tick evasion influence the outcomes following immunization protocols?

Ticks are a major concern to human health and livestock worldwide, being responsible for economic losses that go beyond billions of US dollars per year. This scenario instigates the development of vaccines against these ectoparasites, emphasized by the fact that the main method of controlling ticks still relies on the use of acaricides, what increases costs and may affect the environment as well as human and animal health. The first commercial vaccines against ectoparasites were produced against the tick Rhipicephalus microplus and their efficacy were based on antibodies. Many additional attempts have been conducted to produce protective immune responses against ticks by immunization with specific antigens and the antibody response has usually been the main target of evaluation. But some controversy still populates the roles possibly performed by humoral responses in tick-mammalian host relationships. This review focuses on the analysis of specific aspects concerning antibodies and ticks, especially the influence of parasite density and evasion/modulation. The immunization trials already described against R. microplus were also compiled and analyzed based on the characteristics of the molecules tested, protocols of immunization and tick challenge. Within these issues, it is discussed if or when antibody levels can be directly correlated with the development of tick resistance, and whether anti-tick protective immune responses generated by infestations may become ineffective under a different tick density. Also, higher titers of antibodies can be correlated with protection or susceptibility to tick infestations, what may be altered following continuous or repeated infestations and differ greatly comparing hosts with distinct genetic backgrounds. Regarding evasion, ticks present a sophisticated mechanism for dealing with antibodies, including Immunoglobulin Binding Proteins (IGBPs), that capture, transport and inject them back into the host, while keeping their properties within the parasite. The comparison of immunization protocols shows a total of 22 molecules already tested in cattle vaccination trials against R. microplus, with the predominance of concealed and dual antigens as well as marked differences in tick challenge schemes. The presence of an antibody evasion apparatus and variable levels of tick resistance when facing different densities of parasites are concerns that should be considered when testing vaccine candidates. Ultimately, more refinement may be necessary to effectively design a cocktail vaccine with tick molecules, which may be needed to be altered and combined in non-competing immune contexts to be universally secure and protective.

From Bench to Field: A Guide to Formulating and Evaluating Anti-Tick Vaccines Delving beyond Efficacy to Effectiveness

Ticks are ubiquitous blood-sucking ectoparasites capable of transmitting a wide range of pathogens such as bacteria, viruses, protozoa, and fungi to animals and humans. Although the use of chemicals (acaricides) is the predominant method of tick-control, there are increasing incidents of acaricide tick resistance. Furthermore, there are concerns over accumulation of acaricide residues in meat, milk and in the environment. Therefore, alternative methods of tick-control have been proposed, of which anti-tick cattle vaccination is regarded as sustainable and user-friendly. Over the years, tremendous progress has been made in identifying and evaluating novel candidate tick vaccines, yet none of them have reached the global market. Until now, Bm86-based vaccines (Gavac™ in Cuba and TickGARD^PLUS™ Australia-ceased in 2010) are still the only globally commercialized anti-tick vaccines. In contrast to Bm86, often, the novel candidate anti-tick vaccines show a lower protection efficacy. Why is this so? In response, herein, the potential bottlenecks to formulating efficacious anti-tick vaccines are examined. Aside from Bm86, the effectiveness of other anti-tick vaccines is rarely assessed. So, how can the researchers assess anti-tick vaccine effectiveness before field application? The approaches that are currently used to determine anti-tick vaccine efficacy are re-examined in this review. In addition, a model is proposed to aid in assessing anti-tick vaccine effectiveness. Finally, based on the principles for the development of general veterinary vaccines, a pipeline is proposed to guide in the development of anti-tick vaccines.

Identification and Characterization of Immunodominant Proteins from Tick Tissue Extracts Inducing a Protective Immune Response against Ixodes ricinus in Cattle

Ixodes ricinus is the main vector of tick-borne diseases in Europe. An immunization trial of calves with soluble extracts of I. ricinus salivary glands (SGE) or midgut (ME) previously showed a strong response against subsequent tick challenge, resulting in diminished tick feeding success. Immune sera from these trials were used for the co-immunoprecipitation of tick tissue extracts, followed by LC-MS/MS analyses. This resulted in the identification of 46 immunodominant proteins that were differentially recognized by the serum of immunized calves. Some of these proteins had previously also drawn attention as potential anti-tick vaccine candidates using other approaches. Selected proteins were studied in more detail by measuring their relative expression in tick tissues and RNA interference (RNAi) studies. The strongest RNAi phenotypes were observed for MG6 (A0A147BXB7), a protein containing eight fibronectin type III domains predominantly expressed in tick midgut and ovaries of feeding females, and SG2 (A0A0K8RKT7), a glutathione-S-transferase that was found to be upregulated in all investigated tissues upon feeding. The results demonstrated that co-immunoprecipitation of tick proteins with host immune sera followed by protein identification using LC-MS/MS is a valid approach to identify antigen–antibody interactions, and could be integrated into anti-tick vaccine discovery pipelines.

Comparative Proteomic Analysis of Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) Tropical and Temperate Lineages: Uncovering Differences During Ehrlichia canis Infection

The tick vector Rhipicephalus sanguineus is established as a complex of closely related species with high veterinary-medical significance, in which the presence of different genetic, morphological, and biological traits has resulted in the recognition of different lineages within taxa. One of the most striking differences in the "temperate" and "tropical" lineages of R. sanguineus (s.l.) is the vector competence to Ehrlichia canis, suggesting that these ticks tolerate and react differently to pathogen infection. The present study addresses the SG and MG proteome of the R. sanguineus tropical and temperate lineages and compares their proteomic profile during E. canis infection. Batches of nymphs from the two lineages were allowed to feed on naïve and experimentally E. canis infected dogs and after molting, adults were dissected, and salivary glands and midgut tissues separated. Samples were screened for the presence of E. canis before proteomic analyses. The representation of the proteins identified in infected and non-infected tissues of each lineage was compared and gene ontology used for protein classification. Results highlight important differences in those proteomic profiles that added to previous reported genetic, biological, behavioral, and morphological differences, strengthening the hypothesis of the existence of two different species. Comparing infected and non-infected tissues, the results show that, while in midgut tissues the response to E. canis infection is similar in the salivary glands, the two lineages show a different pattern of protein representation. Focusing on the proteins found only in the infected condition, the data suggests that the cement cone produced during tick feeding may be implicated in pathogen infection. This study adds useful information to the debate on the controversial R. sanguineus systematic status, to the discussion related with the different vectorial competence occurring between the two lineages and identifies potential targets for efficient tick and tick-borne disease control.

Sequence identification and expression profile of seven Dermacentor marginatus glutathione S-transferase genes

Dermacentor marginatus is a widespread tick species and a vector of many pathogens in Eurasia. Due to the medical importance of D. marginatus, control measures are needed for this tick species. Currently tick control approaches rely mostly on acaricide application, whereas wrong and irrational acaricide use may result in drug resistance and residue problems. Vaccination as an alternative approach for tick control has been proven to be effective towards some tick species. However, immunization against D. marginatus has not yet reached satisfactory protection. The effort of in silico based analysis could predict antigenicity and identify candidates for anti-tick vaccine development. We carried out an in silico analysis of D. marginatus glutathione S-transferases (DmGSTs) in order to identify blood-feeding induced GSTs as antigens that can be used in anti-tick vaccine development. Phylogenetic analysis, linear B-cell epitope prediction, homology modeling, and conformational B-cell epitope mapping on the GST models were performed to identify highly antigenic DmGSTs. Relative gene expressions of the seven GSTs were profiled through real-time quantitative PCR (RT-qPCR) to outline GSTs up-regulated during blood feeding. The phylogenetic analysis indicated that the seven GSTs belonged to four classes of GST, including one in epsilon-class, one in zeta-class, one in omega-class, and four in mu-class. Linear B-cell epitope prediction revealed mu-class GSTs share similar conserved antigenic regions. The conformational B-cell epitope mapped on the homology model of the GSTs displayed that GSTs of mu-class showed stronger antigenicity than that of other classes. RT-qPCR revealed DmGSTM1 and DmGSTM2 were positively related to blood feeding. In sum, the data suggest that DmGSTM1 and DmGSTM2 could be tested for potential anti-tick vaccine trials.

Identification and functional analysis of ferritin 2 from the Taiga tick Ixodes persulcatus Schulze

Ferritin 2 (FER2) is an iron storage protein, which has been shown to be critical for iron homeostasis during blood feeding and reproduction in ticks and is therefore suitable as a component for anti-tick vaccines. In this study, we identified the FER2 of Ixodes persulcatus, a major vector for zoonotic diseases such as Lyme borreliosis and tick-borne relapsing fever in Japan, and investigated its functions. Ixodes persulcatus-derived ferritin 2 (Ip-FER2) showed concentration-dependent iron-binding ability and high amino acid conservation, consistent with FER2s of other tick species. Vaccines containing the recombinant Ip-FER2 elicited a significant reduction of the engorgement weight of adult I. persulcatus. Interestingly, the reduction of engorgement weight was also observed in Ixodes ovatus, a sympatric species of I. persulcatus. In silico analyses of FER2 sequences of I. persulcatus and other ticks showed a greater similarity with I. scapularis and I. ricinus and lesser similarity with Hyalomma anatolicum, Haemaphysalis longicornis, Rhipicephalus microplus, and R. appendiculatus. Moreover, it was observed that the tick FER2 sequences possess conserved regions within the primary structures, and in silico epitope mapping analysis revealed that antigenic regions were also conserved, particularly among Ixodes spp ticks. In conclusion, the data support further protective tick vaccination applications using the Ip-FER2 antigens identified herein.

Cocktail Anti-Tick Vaccines: The Unforeseen Constraints and Approaches toward Enhanced Efficacies

Ticks are second to mosquitoes as vectors of disease. Ticks affect livestock industries in Asia, Africa and Australia at ~$1.13 billion USD per annum. For instance, 80% of the global cattle population is at risk of infestation by the Rhipicephalus microplus species-complex, which in 2016 was estimated to cause $22-30 billion USD annual losses. Although the management of tick populations mainly relies on the application of acaricides, this raises concerns due to tick resistance and accumulation of chemical residues in milk, meat, and the environment. To counteract acaricide-resistant tick populations, immunological tick control is regarded among the most promising sustainable strategies. Indeed, immense efforts have been devoted toward identifying tick vaccine antigens. Until now, Bm86-based vaccines have been the most effective under field conditions, but they have shown mixed success worldwide. Currently, of the two Bm86 vaccines commercialized in the 1990s (GavacTM in Cuba and TickGARDPLUSTM in Australia), only GavacTM is available. There is thus growing consensus that combining antigens could broaden the protection range and enhance the efficacies of tick vaccines. Yet, the anticipated outcomes have not been achieved under field conditions. Therefore, this review demystifies the potential limitations and proposes ways of sustaining enhanced cocktail tick vaccine efficacy.

Prediction, mapping and validation of tick glutathione S-transferase B-cell epitopes

In search of ways to address the increasing incidence of global acaricide resistance, tick control through vaccination is regarded as a sustainable alternative approach. Recently, a novel cocktail antigen tick-vaccine was developed based on the recombinant glutathione S-transferase (rGST) anti-sera cross-reaction to glutathione S-transferases of Rhipicephalus appendiculatus (GST-Ra), Amblyomma variegatum (GST-Av), Haemaphysalis longicornis (GST-Hl), Rhipicephalus decoloratus (GST-Rd) and Rhipicephalus microplus (GST-Rm). Therefore, the current study aimed to predict the shared B-cell epitopes within the GST sequences of these tick species. Prediction of B-cell epitopes and proteasomal cleavage sites were performed using immunoinformatics algorithms. The conserved epitopes predicted within the sequences were mapped on the homodimers of the respective tick GSTs, and the corresponding peptides were independently used for rabbit immunization experiments. Based on the dot blot assay, the immunogenicity of the peptides and their potential to be recognized by corresponding rGST anti-sera raised by rabbit immunization in a previous work were investigated. This study revealed that the predicted conserved B-cell epitopes within the five tick GST sequences were localized on the surface of the respective GST homodimers. The epitopes of GST-Ra, GST-Rd, GST-Av, and GST-Hl were also shown to contain a seven residue-long peptide sequence with no proteasomal cleavage sites, whereas proteasomal digestion of GST-Rm was predicted to yield a 4-residue fragment. Given that a few proteasomal cleavage sites were found within the conserved epitope sequences of the four GSTs, the sequences could also contain a T-cell epitope. Finally, the peptide and rGST anti-sera reacted against the corresponding peptide, confirming their immunogenicity. These data support the claim that the rGSTs, used in the previous study, contain conserved B-cell epitopes, which elucidates why the rGST anti-sera cross-reacted to non-homologous tick GSTs. Taken together, the data suggest that the B-cell epitopes predicted in this study could be useful for constituting epitope-based GST tick vaccines.

Caracterization of glutathione S-transferase of Dermacantor marginatus and effect of the recombinant antigen as a potential anti-tick vaccine

Dermacentor marginatus is one of the main tick species in northwestern China, and is a vector of various tick-borne pathogens. Tick control method largely depends on chemical agents, but the disadvantages of using such approach would cause environmental damage and the risk of developing tick resistance to acaricides. Vaccination of tick protective antigen is an eco-friendly approach which is an alternative and promising method to mitigate tick infestation in livestock. In the study, a mu-class glutathione S-transferase (GST) sequence of D. marginatus was cloned and the recombinant protein (rDmGST) was expressed. Transcriptional level of the GST was measured together with native GST activity of the tick. Finally, A vaccine trial on rabbits against D. marginatus was proceeded to evaluate the anti-tick effect of rDmGST. Results reveled that the CDs of the D. margiantus glutathione S-transferase mu 1 gene has 669 base pair nucleotide sequence encoding a 223 amino acid. The deduced GST protein sequence had over 95 % similarity with that of D. variabilis. The rDmGST was efficiently expressed soluble and purified by His trap affinity chromatography. Enzyme activity of native GST and transcriptional profiles of the GST showed up-regulation in different stages and organs of D. marginaus during blood feeding. Polyclonal antibody reacted with rDmGST in Western blotting. Tick challenge on rDmGST inoculated rabbits showed reductions in adult female engorgement rate, total egg mass and egg hatching rate with an overall vaccine efficacy of 43.69 %. The results of the experiment indicated the GST has potential value to be an effective protective antigen of D. marginatus.

The case for oxidative stress molecule involvement in the tick-pathogen interactions -an omics approach

The blood-feeding behavior of ticks has resulted in them becoming one of the most important vectors of disease-causing pathogens. Ticks possess a well-developed innate immune system to counter invading pathogens. However, the coevolution of ticks with tick-borne pathogens has adapted these pathogens to the tick's physiology and immune response through several mechanisms including transcriptional regulation. The recent development in tick and tick-borne disease research greatly involved the "omics" approach. The omics approach takes a look en masse at the different genes, proteins, metabolomes, and the microbiome of the ticks that could be differentiated during pathogen infection. Data from this approach revealed that oxidative stress-related molecules in ticks are differentiated and possibly being exploited by the pathogens to evade the tick's immune response. In this study, we review and discuss transcriptomic and proteomic data for some oxidative stress molecules differentially expressed during pathogen infection. We also discuss metabolomics and microbiome data as well as functional genomics in order to provide insight into the tick-pathogen interaction.