Sequence characterization and immunogenicity of cystatins from the cattle tick Rhipicephalus (Boophilus) microplus

A longitudinal transcriptomic analysis of Rhipicephalus microplus midgut upon feeding

Rhipicephalus microplus, a highly host-specific tick that primarily feeds on cattle, posing a significant threat to livestock production. The investigation of tick physiology is crucial for identifying potential targets in tick control. Of particular interest adult female ticks undergo a significant expansion of the midgut during feeding, leading to an over 100-fold increase in body weight. Beyond the functions of storing and digesting blood meals, the tick midgut plays a crucial role in acquiring and transmitting pathogens. However, our understanding of tick midgut physiology remains limited. In this study we conducted a comprehensive longitudinal transcriptome analysis of the midgut from adult female R. microplus ticks collected at various feeding stages, providing an overview of the transcriptional modulation in this organ as feeding progress. By employing a de novo assembly approach followed by coding-sequences (CDS) extraction, 60,599 potential CDS were identified. In preparation for functional annotation and differential expression analysis, transcripts that showed an average transcript per million (TPM) ≥ 3 in at least one of the biological conditions were extracted. This selection process resulted in a total of 10,994 CDS, which were categorized into 24 functional classes. Notably, our differential expression analysis revealed three main transcriptional profiles. In the first one, representing the slow-feeding stage, the most abundant functional classes were the "protein synthesis" and "secreted" groups, reflecting the highly active state of the tick midgut. The second profile partially accounts for the rapid-feeding stage, in which a high number of differentially expressed transcripts was observed. Lastly, the third transcriptional profile represents post-detached ticks. Notably the highest number of modulated transcripts was observed up to 48 h post-detachment (hpd), however no major differences was observed up to 168 hpd. Overall, the data presented here offers a temporal insight into tick midgut physiology, contributing to the identification of potential targets for the development of anti-tick control strategies.

Changes in saliva protein profile throughout Rhipicephalus microplus blood feeding

BACKGROUND

When feeding on a vertebrate host, ticks secrete saliva, which is a complex mixture of proteins, lipids, and other molecules. Tick saliva assists the vector in modulating host hemostasis, immunity, and tissue repair mechanisms. While helping the vector to feed, its saliva modifies the site where pathogens are inoculated and often facilitates the infection process. The objective of this study is to uncover the variation in protein composition of Rhipicephalus microplus saliva during blood feeding.

METHODS

Ticks were fed on calves, and adult females were collected, weighed, and divided in nine weight groups, representing the slow and rapid feeding phases of blood feeding. Tick saliva was collected, and mass spectrometry analyses were used to identify differentially secreted proteins. Bioinformatic tools were employed to predict the structural and functional features of the salivary proteins. Reciprocal best hit analyses were used to identify conserved families of salivary proteins secreted by other tick species.

RESULTS

Changes in the protein secretion profiles of R. microplus adult female saliva during the blood feeding were observed, characterizing the phenomenon known as "sialome switching." This observation validates the idea that the switch in protein expression may serve as a mechanism for evading host responses against tick feeding. Cattle tick saliva is predominantly rich in heme-binding proteins, secreted conserved proteins, lipocalins, and protease inhibitors, many of which are conserved and present in the saliva of other tick species. Additionally, another remarkable observation was the identification of host-derived proteins as a component of tick saliva.

CONCLUSIONS

Overall, this study brings new insights to understanding the dynamics of the proteomic profile of tick saliva, which is an important component of tick feeding biology. The results presented here, along with the disclosed sequences, contribute to our understanding of tick feeding biology and might aid in the identification of new targets for the development of novel anti-tick methods.

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.

Low Genetic Polymorphism in the Immunogenic Sequences of Rhipicephalus microplus Clade C

Rhipicephalus microplus tick highly affects the veterinary sector throughout the world. Different tick control methods have been adopted, and the identification of tick-derived highly immunogenic sequences for the development of an anti-tick vaccine has emerged as a successful alternate. This study aimed to characterize immunogenic sequences from R. microplus ticks prevalent in Pakistan. Ticks collected in the field were morphologically identified and subjected to DNA and RNA extraction. Ticks were molecularly identified based on the partial mitochondrial cytochrome C oxidase subunit (cox) sequence and screened for piroplasms (Theileria/Babesia spp.), Rickettsia spp., and Anaplasma spp. PCR-based pathogens-free R. microplus-derived cDNA was used for the amplification of full-length cysteine protease inhibitor (cystatin 2b), cathepsin L-like cysteine proteinase (cathepsin-L), glutathione S-transferase (GST), ferritin 1, 60S acidic ribosomal protein (P0), aquaporin 2, ATAQ, and R. microplus 05 antigen (Rm05Uy) coding sequences. The cox sequence revealed 100% identity with the nucleotide sequences of Pakistan's formerly reported R. microplus, and full-length immunogenic sequences revealed maximum identities to the most similar sequences reported from India, China, Cuba, USA, Brazil, Egypt, Mexico, Israel, and Uruguay. Low nonsynonymous polymorphisms were observed in ATAQ (1.5%), cathepsin-L (0.6%), and aquaporin 2 (0.4%) sequences compared to the homologous sequences from Mexico, India, and the USA, respectively. Based on the cox sequence, R. microplus was phylogenetically assembled in clade C, which includes R. microplus from Pakistan, Myanmar, Malaysia, Thailand, Bangladesh, and India. In the phylogenetic trees, the cystatin 2b, cathepsin-L, ferritin 1, and aquaporin 2 sequences were clustered with the most similar available sequences of R. microplus, P0 with R. microplus, R. sanguineus and R. haemaphysaloides, and GST, ATAQ, and Rm05Uy with R. microplus and R. annulatus. This is the first report on the molecular characterization of clade C R. microplus-derived immunogenic sequences.

Novel Cysteine Protease Inhibitor Derived from the Haementeria vizottoi Leech: Recombinant Expression, Purification, and Characterization

Cathepsin L (CatL) is a lysosomal cysteine protease primarily involved in the terminal degradation of intracellular and endocytosed proteins. More specifically, in humans, CatL has been implicated in cancer progression and metastasis, as well as coronary artery diseases and others. Given this, the search for potent CatL inhibitors is of great importance. In the search for new molecules to perform proteolytic activity regulation, salivary secretions from hematophagous animals have been an important source, as they present protease inhibitors that evolved to disable host proteases. Based on the transcriptome of the Haementeria vizzotoi leech, the cDNA of Cystatin-Hv was selected for this study. Cystatin-Hv was expressed in Pichia pastoris and purified by two chromatographic steps. The kinetic results using human CatL indicated that Cystatin-Hv, in its recombinant form, is a potent inhibitor of this protease, with a K_i value of 7.9 nM. Consequently, the present study describes, for the first time, the attainment and the biochemical characterization of a recombinant cystatin from leeches as a potent CatL inhibitor. While searching out for new molecules of therapeutic interest, this leech cystatin opens up possibilities for the future use of this molecule in studies involving cellular and in vivo models.

Mechanisms of amitraz resistance in a Rhipicephalus microplus strain from southern Brazil

Amitraz is one of the most used acaricides for the control of ticks of domestic animals, however, extensive use of this active ingredient has favored the development of resistant populations of Rhipicephalus microplus worldwide. The possible mechanisms of metabolic and/or target-site alterations mechanisms of amitraz resistance were investigated in a Brazilian field population of R. microplus (São Gabriel strain). Bioassays with the synergists piperonylbutoxide, triphenylphosphate and diethyl-maleate were used to evaluate the metabolic mechanisms involved. Target-site insensitivity was investigated by amplification and sequencing of a fragment of the octopamine/tyramine (OCT/TYR) receptor gene. Piperonylbutoxide synergism (synergism ratio = 2.8) indicated the participation of the P450 pathway in the detoxification of amitraz. Previously reported single nucleotide polymorphisms that confer amino acid changes in the OCT/TYR receptor, threonine to proline (T8P) and leucine to serine (L22S), were found in the amitraz-resistant strain but not in the susceptible reference strain. The results suggest that amitraz resistance in the studied strain is multi-factorial and may result from cytochrome P450 detoxification and mutations in octopamine receptors.

Mialostatin, a Novel Midgut Cystatin from Ixodes ricinus Ticks: Crystal Structure and Regulation of Host Blood Digestion

The hard tick Ixodes ricinus is a vector of Lyme disease and tick-borne encephalitis. Host blood protein digestion, essential for tick development and reproduction, occurs in tick midgut digestive cells driven by cathepsin proteases. Little is known about the regulation of the digestive proteolytic machinery of I. ricinus. Here we characterize a novel cystatin-type protease inhibitor, mialostatin, from the I. ricinus midgut. Blood feeding rapidly induced mialostatin expression in the gut, which continued after tick detachment. Recombinant mialostatin inhibited a number of I. ricinus digestive cysteine cathepsins, with the greatest potency observed against cathepsin L isoforms, with which it co-localized in midgut digestive cells. The crystal structure of mialostatin was determined at 1.55 Å to explain its unique inhibitory specificity. Finally, mialostatin effectively blocked in vitro proteolysis of blood proteins by midgut cysteine cathepsins. Mialostatin is likely to be involved in the regulation of gut-associated proteolytic pathways, making midgut cystatins promising targets for tick control strategies.

Rhipicephalus microplus cystatin as a potential cross-protective tick vaccine against Rhipicephalus appendiculatus

Rhipicephalus appendiculatus, the brown ear tick, is an important disease vector of livestock in eastern, central and southern Africa. Rhipicephalus appendiculatus acaricide resistance requires the search for alternative methods for its control. Cystatins constitute a superfamily of cysteine peptidase inhibitors vital for tick blood feeding and development. These inhibitors were proposed as antigens in anti-tick vaccines. In this work, we applied structural and biochemical approaches to characterize a new cystatin named R. appendiculatus cystatin 2a (Racys2a). Structural modeling showed that this new protein possesses characteristic type 2 cystatin motifs, besides conservation of other structural patterns along the protein. Peptidase inhibitory assays with recombinant Racys2a showed modulation of tick and host cathepsins involved in blood digestion and immune system responses, respectively. A heterologous tick challenge with R. appendiculatus in rabbits immunized with recombinant Rhipicephalus microplus cystatin 2c (rBmcys2c) was performed to determine cross-reactivity. Histological staining showed that rBmcys2c vaccination caused damage to the gut, salivary gland and ovary tissues in R. appendiculatus. Furthermore, cystatin vaccine reduced the number of fully engorged adult females in 11.5 %. Consequently, strategies to increase the protection rate are necessary, including the selection of two or more antigens to compose a vaccine cocktail.

Immunosuppressive effects of sialostatin L1 and L2 isolated from the taiga tick Ixodes persulcatus Schulze

Tick saliva contains immunosuppressants which are important to obtain a blood meal and enhance the infectivity of tick-borne pathogens. In Japan, Ixodes persulcatus is a major vector for Lyme borreliosis pathogens, such as Borrelia garinii, as well as for those causing relapsing fever, such as B. miyamotoi. To date, little information is available on bioactive salivary molecules, produced by this tick. Thus, in this study, we identified two proteins, I. persulcatus derived sialostatin L1 (Ip-sL1) and sL2 (Ip-sL2), as orthologs of I. scapularis derived sL1 and sL2. cDNA clones of Ip-sL1 and Ip-sL2 shared a high identity with sequences of sL1 and sL2 isolated from the salivary glands of I. scapularis. Semi-quantitative PCR revealed that Ip-sL1 and Ip-sL2 were expressed in the salivary glands throughout the life of the tick. In addition, Ip-sL1 and Ip-sL2 were expressed even before the ticks started feeding, and their expression continued during blood feeding. Recombinant Ip-sL1 and Ip-sL2 were developed to characterize the proteins via biological and immunological analyses. These analyses revealed that both Ip-sL1 and Ip-sL2 had inhibitory effects on cathepsins L and S. Ip-sL1 and Ip-sL2 inhibited the production of IP-10, TNFα, and IL-6 by LPS-stimulated bone-marrow-derived dendritic cells (BMDCs). Additionally, Ip-sL1 significantly impaired BMDC maturation. Taken together, these results suggest that Ip-sL1 and Ip-sL2 confer immunosuppressive functions and appear to be involved in the transmission of pathogens by suppressing host immune responses, such as cytokine production and dendritic cell maturation. Therefore, further studies are warranted to investigate the immunosuppressive functions of Ip-sL1 and Ip-sL2 in detail to clarify their involvement in pathogen transmission via I. persulcatus.

De novo transcriptome sequencing and comparative analysis of Haemaphysalis flava Neumann, 1897 at larvae and nymph stages

Haemaphysalis flava Neumann, 1897 (H. flava) is of public health significance due to its capability of transmitting several pathogens such as Rickettsia, Ehrlichia, Bartonella and Francisella tularensis. However, lack of complete genome, transcriptome and proteome information limits the understanding of the biology of H. flava. Here, the total RNA of H. flava was collected separately at larvae and nymph stages and analyzed with high-throughput RNA sequencing technology. The obtained data were assembled and annotated based on the near origin species in the Nr database. The functions of the unigenes were annotated and classified by seven databases, including Nr, Nt, Pfam, KOG, Swiss-Prot, GO and KEGG. A total of 61,850,967 and 79,579,368 clean reads were obtained with a data bulk of 9.28 G and 11.94 G in larvae and nymph stages, respectively. The number of unigenes was 440,896, with 48.6% of them being matched to the Nr database and 51.4% remaining unknown. Additionally, 1,776,404 SNPs were identified in the unigenes. Differential analysis revealed 80 differentially expressed genes (DEGs), including 56 up-regulated genes and 24 down-regulated genes in the nymph versus larvae. qPCR confirmed 4 of the 56 up-regulated genes and 4 of the down-regulated genes. KEGG analysis of the DEGs showed that aldehyde dehydrogenase and sorbitol dehydrogenase, two up-regulated unigenes in nymph versus larvae, were both matched to the top three enriched pathways: "chloroalkane and chloroalkene degradation", "fatty acid degradation" and "glycolysis and gluconeogenesis". This is the first report on the whole transcriptome of H. flava at larvae and nymph stages. This study contributes to the understanding of H. flava at the gene expression level in different developmental stages and provides a theoretical basis for the development of vaccines against H. flava.

Proteomic analysis of saliva from partially and fully engorged adult female Rhipicephalus microplus (Acari: Ixodidae)

Rhipicephalus microplus salivary gland secretes a number of complex bioactive proteins during feeding. These components are important in feeding and affect anti-coagulation, anti-inflammation and also have anti-microbial effects. In this study, tick saliva was collected from partially engorged female (PEF) and fully engorged female (FEF) ticks. Liquid chromatography tandem-mass spectrometry (LC-MS/MS) and isobaric tags for relative and absolute quantification (iTRAQ) were used to identify and quantify R. microplus salivary proteins. A total of 322 unique peptides were detected and 151 proteins were characterized in both PEF and FEF. Of these, 41 proteins are considered as high-confidence proteins. Fifteen high-confidence proteins were upregulated and six high-confidence proteins were downregulated (p < 0.05; PEF:FEF ratio ≥ 1.2 or PEF:FEF ratio ≤ 0.83); 17 high-confidence proteins are slightly changed (PEF:FEF ratio > 0.83 and < 1.2). These high-confidence proteins are involved in several physiological roles, including egg development, transportation of proteins, immunity and anti-microorganism, anti-coagulant, and adhesion. In comparison with PEF, the number of upregulated proteins exceeded the number of proteins downregulated. Salivary protein may be induced by the blood-meal and these proteins contribute to successful feeding.

Chemical Equilibrium at the Tick-Host Feeding Interface:A Critical Examination of Biological Relevance in Hematophagous Behavior

Ticks secrete hundreds to thousands of proteins into the feeding site, that presumably all play important functions in the modulation of host defense mechanisms. The current review considers the assumption that tick proteins have functional relevance during feeding. The feeding site may be described as a closed system and could be treated as an ideal equilibrium system, thereby allowing modeling of tick-host interactions in an equilibrium state. In this equilibrium state, the concentration of host and tick proteins and their affinities will determine functional relevance at the tick-host interface. Using this approach, many characterized tick proteins may have functional relevant concentrations and affinities at the feeding site. Conversely, the feeding site is not an ideal closed system, but is dynamic and changing, leading to possible overestimation of tick protein concentration at the feeding site and consequently an overestimation of functional relevance. Ticks have evolved different possible strategies to deal with this dynamic environment and overcome the barrier that equilibrium kinetics poses to tick feeding. Even so, cognisance of the limitations that equilibrium binding place on deductions of functional relevance should serve as an important incentive to determine both the concentration and affinity of tick proteins proposed to be functional at the feeding site.

Peptidase inhibitors in tick physiology

Peptidase inhibitors regulate a wide range of physiological processes involved in the interaction between hematophagous parasites and their hosts, including tissue remodeling, the immune response and blood coagulation. In tick physiology, peptidase inhibitors have a crucial role in adaptation to improve parasitism mechanisms, facilitating blood feeding by interfering with defense-related host peptidases. Recently, a larger number of studies on this topic led to the description of several new tick inhibitors displaying interesting novel features, for example a role in pathogen transmission to the host. A comprehensive review discussing these emerging concepts can therefore shed light on peptidase inhibitor functions, their relevance to tick physiology and their potential applications. Here, we summarize and examine the general characteristics, functional diversity and action of tick peptidase inhibitors with known physiological roles in the tick-host-pathogen interaction.

Molecular and structural characterization of novel cystatins from the taiga tick Ixodes persulcatus

Cystatins are cysteine peptidase inhibitors that in ticks mediate processes such as blood feeding and digestion. The ixodid tick Ixodes persulcatus is endemic to the Eurasia, where it is the principal vector of Lyme borreliosis. To date, no I. persulcatus cystatin has been characterized. In the present work, we describe three novel cystatins from I. persulcatus, named JpIpcys2a, JpIpcys2b and JpIpcys2c. In addition, the potential of tick cystatins as cross-protective antigens was evaluated by vaccination of hamsters using BrBmcys2c, a cystatin from Rhipicephalus microplus, against I. persulcatus infestation. Sequence analysis showed that motifs that are characteristic of cystatins type 2 are fully conserved in JpIpcys2b, while mutations are present in both JpIpcys2a and JpIpcys2c. Protein-protein docking simulations further revealed that JpIpcys2a, JpIpcys2b and JpIpcys2c showed conserved binding sites to human cathepsins L, all of them covering the active site cleft. Cystatin transcripts were detected in different I. persulcatus tissues and instars, showing their ubiquitous expression during I. persulcatus development. Serological analysis showed that although hamsters immunized with BrBmcys2c developed a humoral immune response, this response was not adequate to protect against a heterologous challenge with I. persulcatus adult ticks. The lack of cross-protection provided by BrBmcys2c immunization is perhaps linked to the fact that cystatins cluster into multigene protein families that are expressed differentially and exhibit functional redundancy. How to target such small proteins that are secreted in low quantities remains a challenge in the development of suitable anti-tick vaccine antigens.

Molecular and functional characterization of Bm05br antigen from Rhipicephalus microplus

Rhipicephalus microplus is a cattle-specific tick, causing considerable losses in the livestock industry. The identification of molecules responsible for modulation of host defenses during different parasite stages can help in the development of alternative methods, such as vaccination, to control tick infestations. Hq05, a protein of unknown function identified in the tick Haemaphysalis qinghaiensis, induced a significant protective immune response when used as a vaccine in sheep. In the present study, we investigated Bm05br, the Hq05 homologous gene from R. microplus. Besides H. qinghaiensis, Bm05br homologous found in other tick species such as Rhipicephalus annulatus, Rhipicephalus sanguineus sensu lato, Haemaphysalis longicornis and Ixodes scapularis were comparatively analyzed. Bm05br expression profile in different R. microplus tissues and life-stages was determined by qRT-PCR and Western blot. Bm05br was detected in ovaries, salivary glands and the fat body of both partially and fully engorged females. The highest transcription levels were observed in partially engorged females fat body and salivary glands. Gene knockdown by RNAi reduced egg hatching rate and the weight of tick larvae obtained from treated group, when compared to controls. These results indicate that Bm05br may be involved in R. microplus reproduction. Together with its distribution and high sequence conservation across different tick species, our data suggest Bm05br as a potential antigen for development of a multispecies anti-tick vaccine.

Strategies for new and improved vaccines against ticks and tick-borne diseases

Ticks infest a variety of animal species and transmit pathogens causing disease in both humans and animals worldwide. Tick-host-pathogen interactions have evolved through dynamic processes that accommodated the genetic traits of the hosts, pathogens transmitted and the vector tick species that mediate their development and survival. New approaches for tick control are dependent on defining molecular interactions between hosts, ticks and pathogens to allow for discovery of key molecules that could be tested in vaccines or new generation therapeutics for intervention of tick-pathogen cycles. Currently, tick vaccines constitute an effective and environmentally sound approach for the control of ticks and the transmission of the associated tick-borne diseases. New candidate protective antigens will most likely be identified by focusing on proteins with relevant biological function in the feeding, reproduction, development, immune response, subversion of host immunity of the tick vector and/or molecules vital for pathogen infection and transmission. This review addresses different approaches and strategies used for the discovery of protective antigens, including focusing on relevant tick biological functions and proteins, reverse genetics, vaccinomics and tick protein evolution and interactomics. New and improved tick vaccines will most likely contain multiple antigens to control tick infestations and pathogen infection and transmission.

Rhipicephalus microplus and Ixodes ovatus cystatins in tick blood digestion and evasion of host immune response

BACKGROUND

Cystatins are a group of cysteine protease inhibitors responsible for physiological proteolysis regulation and present in a wide range of organisms. Studies about this class of inhibitors in parasites have contributed to clarify their roles in important physiological processes, like blood digestion and modulation of host immune response during blood feeding. Thus, cystatins are a subject of research on the development of new parasite control methods. Additionally, the characterization of proteins shared by different parasite species represents a valuable strategy to find potential targets in multi-species control methods. However, cystatin functions in ticks remain undetermined, especially in Rhipicephalus microplus and Ixodes ovatus, two species that affect livestock and human health, respectively.

METHODS

Here we report the inhibitory profile of two R. microplus (BrBmcys2b and BrBmcys2c) and one I. ovatus (JpIocys2a) cystatins to commercial cathepsins B, C, and L. The presence of native cystatins in R. microplus tissues was analyzed using sera against recombinant BrBmcys2b and BrBmcys2c. Also, a peptide from JpIocys2a was synthesized for rabbit immunization, and this serum was used to analyze the cross antigenicity between R. microplus and I. ovatus cystatins.

RESULTS

Enzymatic inhibition profile of tick cystatins shows a distinct modulation for cathepsins related to tick blood digestion and evasion of host immune response. Furthermore, BrBmcys2b was detected in saliva and different tissues along tick stages, while BrBmcys2c was detected mainly in gut from partially engorged R. microplus females, demonstrating a distinct pattern of cystatin expression, secretion and traffic between tick tissues. Moreover, phylogenetic analysis suggests that JpIocys2a belongs to the group of tick gut secreted cystatins. Finally, cross-antigenicity assays revealed that antibodies against the JpIocys2a peptide recognize native and recombinant R. microplus cystatins.

CONCLUSION

The presence of these proteins in different tissues and their ability to differentially inhibit cathepsins suggest distinct roles for JpIocys2a, BrBmcys2b, and BrBmcys2c in blood digestion, egg and larvae development, and modulation of host immune response in tick physiology. The cross-antigenicity between native and recombinant cystatins supports further experiments using JpIocys2a, BrBmcys2b, and BrBmcys2c as vaccine antigens.

Reprolysin metalloproteases from Ixodes persulcatus, Rhipicephalus sanguineus and Rhipicephalus microplus ticks

Metalloproteases (MPs) have been considered essential for blood feeding and other physiological functions in several hematophagous animals, including ticks. We report the characterization of MP sequences of three important ticks from Asia, Africa and America: Ixodes persulcatus (Ip-MPs), Rhipicephalus sanguineus (Rs-MPs) and R. microplus (BrRm-MPs). Amino acid sequence identity between R. microplus and R. sanguineus MPs ranged from 76 to 100 %, and identities among I. persulcatus, I. ricinus and I. scapularis MP sequences ranged from 88 to 97 %. This high sequence identity and typical functional motifs show that all sequences are MPs. The presence of a zinc binding site, a Met-turn and cysteine rich domain at the C-terminal region indicates that these proteins belong to the reproplysin family of MPs. Differences in amino acid sequences of BrRm-MP1, BrRm-MP2, BrRm-MP4 and BrRm-MP5 (from Porto Alegre strain ticks) were 6, 2, 7 and 5 %, respectively, when compared with sequences deposited in GenBank for the same genes from other R. microplus isolates. Analyses of MPs predicted that they have various highly antigenic regions. Semi-quantitative RT-PCR analysis revealed the presence of transcripts in salivary glands of partially and fully fed female ticks. None of these transcripts were observed in males (except BrRm-MP4) and eggs. These enzymes may be functional components required during tick feeding to manipulate host defenses and support tick hematophagy.

A 24-48 h fed Amblyomma americanum tick saliva immuno-proteome

BACKGROUND

Multiple tick saliva proteins, the majority of which are unknown, confer tick resistance in repeatedly infested animals. The objective of this study was to identify the 24-48 h fed Amblyomma americanum tick saliva immuno-proteome. The 24-48 h tick-feeding phase is critical to tick parasitism as it precedes important events in tick biology, blood meal feeding and disease agent transmission. Fed male, 24 and 96 h fed female phage display cDNA expression libraries were biopanned using rabbit antibodies to 24 and 48 h fed A. americanum female tick saliva proteins. Biopanned immuno-cDNA libraries were subjected to next generation sequencing, de novo assembly, and bioinformatic analysis.

RESULTS

More than 800 transcripts that code for 24-48 h fed A. americanum immuno-proteins are described. Of the 895 immuno-proteins, 52% (464/895) were provisionally identified based on matches in GenBank. Of these, ~19% (86/464) show high level of identity to other tick hypothetical proteins, and the rest include putative proteases (serine, cysteine, leukotriene A-4 hydrolase, carboxypeptidases, and metalloproteases), protease inhibitors (serine and cysteine protease inhibitors, tick carboxypeptidase inhibitor), and transporters and/or ligand binding proteins (histamine binding/lipocalin, fatty acid binding, calreticulin, hemelipoprotein, IgG binding protein, ferritin, insulin-like growth factor binding proteins, and evasin). Others include enzymes (glutathione transferase, cytochrome oxidase, protein disulfide isomerase), ribosomal proteins, and those of miscellaneous functions (histamine release factor, selenoproteins, tetraspanin, defensin, heat shock proteins).

CONCLUSIONS

Data here demonstrate that A. americanum secretes a complex cocktail of immunogenic tick saliva proteins during the first 24-48 h of feeding. Of significance, previously validated immunogenic tick saliva proteins including AV422 protein, calreticulin, histamine release factor, histamine binding/lipocalins, selenoproteins, and paramyosin were identified in this screen, supporting the specificity of the approach in this study. While descriptive, this study opens opportunities for in-depth tick feeding physiology studies.

Proteomic analysis of cattle tick Rhipicephalus (Boophilus) microplus saliva: a comparison between partially and fully engorged females

The cattle tick Rhipicephalus (Boophilus) microplus is one of the most harmful parasites affecting bovines. Similarly to other hematophagous ectoparasites, R. microplus saliva contains a collection of bioactive compounds that inhibit host defenses against tick feeding activity. Thus, the study of tick salivary components offers opportunities for the development of immunological based tick control methods and medicinal applications. So far, only a few proteins have been identified in cattle tick saliva. The aim of this work was to identify proteins present in R. microplus female tick saliva at different feeding stages. Proteomic analysis of R. microplus saliva allowed identifying peptides corresponding to 187 and 68 tick and bovine proteins, respectively. Our data confirm that (i) R. microplus saliva is complex, and (ii) that there are remarkable differences in saliva composition between partially engorged and fully engorged female ticks. R. microplus saliva is rich mainly in (i) hemelipoproteins and other transporter proteins, (ii) secreted cross-tick species conserved proteins, (iii) lipocalins, (iv) peptidase inhibitors, (v) antimicrobial peptides, (vii) glycine-rich proteins, (viii) housekeeping proteins and (ix) host proteins. This investigation represents the first proteomic study about R. microplus saliva, and reports the most comprehensive Ixodidae tick saliva proteome published to date. Our results improve the understanding of tick salivary modulators of host defense to tick feeding, and provide novel information on the tick-host relationship.