Longistatin, a plasminogen activator, is key to the availability of blood-meals for ixodid ticks

A novel chemokine binding protein 1-like gene is vital for the blood pool development and engorgement of the hard tick Haemaphysalis longicornis

Tick saliva modulates host responses during a blood feeding process. We identified a novel chemokine binding protein 1-like (HLCBP1-like) gene from the salivary glands of the Asian longhorned tick, Haemaphysalis longicornis. The HLCBP1-like protein, lacking a well-defined conserved domain, showed structural similarity to evasin, a chemokine binding protein from the brown dog tick, Rhipicephalus sanguineus. A preliminary knockdown study of HLCBP1-like revealed that ticks with reduced expression of this gene, halted feeding in the early feeding phase, and did not fully-engorge, unlike the control dsRNA (malE) injected ticks. Also, knockdown ticks induced cellular immune responses in the host skin, similar to control dsmalE-injected ticks, but did not show hemorrhage. These findings suggest that HLCBP1-like may play a modulatory role in the slow feeding phase.

Binding Molecules in Tick Saliva for Targeting Host Cytokines, Chemokines, and Beyond

Ticks have coevolved with their hosts over millions of years, developing the ability to evade hemostatic, inflammatory, and immunological responses. Salivary molecules from these vectors bind to cytokines, chemokines, antibodies, complement system proteins, vasodilators, and molecules involved in coagulation and platelet aggregation, among others, inhibiting or blocking their activities. Initially studied to understand the complexities of tick-host interactions, these molecules have been more recently recognized for their potential clinical applications. Their ability to bind to soluble molecules and modulate important physiological systems, such as immunity, hemostasis, and coagulation, positions them as promising candidates for future therapeutic development. This review aims to identify the binding molecules present in tick saliva, determine their primary targets, and explore the tick species involved in these processes. By associating the binding molecules, the molecules to which they bind, and the effect caused, the review provides a basis for understanding how these molecules can contribute to possible future advances in clinical applications.

Receptor for Advanced Glycation End Product (RAGE) Modulates Inflammation During Feeding of the Hard Tick, Haemaphysalis longicornis in Mice

Ticks are notorious blood-sucking ectoparasites that affect both humans and animals. They serve as a unique vector of various deadly diseases. Here, we have shown the roles of the receptor for advanced glycation end products (RAGE) during repeated infestations by the tick Haemaphysalis longicornis using RAGE-/- mice. In primary infestation, a large blood pool developed, which was flooded with numerous RBCs, especially during the rapid feeding phase of the tick both in wild-type (wt) and RAGE-/- mice. Very few inflammatory cells were detected around the zones of haemorrhage in the primary infestations. However, the number of inflammatory cells gradually increased in the subsequent tick infestations, and during the third infestations, the number of inflammatory cells reached to the highest level (350.3 ± 16.8 cells/focus). The site of attachment was totally occupied by the inflammatory cells in wt mice, whereas very few cells were detected at the ticks' biting sites in RAGE-/- mice. RAGE was highly expressed during the third infestation in wt mice. In the third infestation, infiltration of CD44+ lymphocytes, eosinophils and expression of S100A8 and S100B significantly increased at the biting sites of ticks in wt, but not in RAGE-/- mice. In addition, peripheral eosinophil counts significantly increased in wt but not in RAGE-/- mice. Taken together, our study revealed that RAGE-mediated inflammation and eosinophils played crucial roles in the tick-induced inflammatory reactions.

Ascaridia galli, a common nematode in semiscavenging indigenous chickens in Bangladesh: epidemiology, genetic diversity, pathobiology, ex vivo culture, and anthelmintic efficacy

Ascaridia galli is the most common nematode in chickens. Ascaridia galli is highly prevalent in chickens reared in scavenging or semiscavenging systems. Here, we studied the epidemiology, pathology, genetic diversity, ex vivo culture protocol and anthelmintic sensitivity of A. galli prevalent in indigenous chickens in Bangladesh. Through morphological study and molecular analyses, the isolated worms were confirmed as A. galli. Of the chickens examined, 45.6% (178 out of 390) were found infected. The male and young chickens were significantly (P < 0.05) more prone to A. galli infection. Prevalence of the infection was significantly (P < 0.05) lower in the summer season. In heavy infections, A. galli blocked the small intestine. Marked inflammation, increased mucus production and petechial hemorrhages were evident in the small intestine, particularly in the duodenum. Also, there were desquamation and adhesion of the mucosal villi; degeneration, necrosis of the epithelial cells and goblet cell hyperplasia. The mucosal layer was infiltrated mainly with eosinophils and heterophils. We developed a hen egg white-based long-term ex vivo culture protocol which supported the survival and reproduction of A. galli for more than a week. Levamisole (LEV) and ivermectin (IVM) efficiently killed A. galli. However, albendazole (ABZ), mebendazole (MBZ), and piperazine (PPZ) did not kill the worms even at 120 μg/mL and 1mg/mL concentrations, respectively. Taken together, our results suggest that A. galli is highly prevalent in semiscavenging chickens in Bangladesh. Ascaridia galli can be easily maintained ex vivo in egg white supplemented M199 medium. LEV and IVM, but not ABZ, MBZ and PPZ, can be used for treating and controlling A. galli infections in chickens.

Who Let the Dogs Out? Unmasking the Neglected: A Semi-Systematic Review on the Enduring Impact of Toxocariasis, a Prevalent Zoonotic Infection

Toxocariasis remains an important neglected parasitic infection representing one of the most common zoonotic infections caused by the parasite Toxocara canis or, less frequently, by Toxocara cati. The epidemiology of the disease is complex due to its transmission route by accidental ingestion of embryonated Toxocara eggs or larvae from tissues from domestic or wild paratenic hosts. Even though the World Health Organization and Centers for Disease Control classified toxocariasis amongst the top six parasitic infections of priority to public health, global epidemiological data regarding the relationship between seropositivity and toxocariasis is limited. Although the vast majority of the infected individuals remain asymptomatic or experience a mild disease, the infection is associated with important health and socioeconomic consequences, particularly in underprivileged, tropical, and subtropical areas. Toxocariasis is a disease with multiple clinical presentations, which are classified into five distinct forms: the classical visceral larva migrans, ocular toxocariasis, common toxocariasis, covert toxocariasis, and cerebral toxocariasis or neurotoxocariasis. Anthelmintic agents, for example, albendazole or mebendazole, are the recommended treatment, whereas a combination with topical or systemic corticosteroids for specific forms is suggested. Prevention strategies include educational programs, behavioral and hygienic changes, enhancement of the role of veterinarians, and anthelmintic regimens to control active infections.

RNA activation in ticks

RNA activation (RNAa) is a burgeoning area of research in which double-stranded RNAs (dsRNAs) or small activating RNAs mediate the upregulation of specific genes by targeting the promoter sequence and/or AU-rich elements in the 3'- untranslated region (3'-UTR) of mRNA molecules. So far, studies on the phenomenon have been limited to mammals, plants, bacteria, Caenorhabditis elegans, and recently, Aedes aegypti. However, it is yet to be applied in other arthropods, including ticks, despite the ubiquitous presence of argonaute 2 protein, which is an indispensable requirement for the formation of RNA-induced transcriptional activation complex to enable a dsRNA-mediated gene activation. In this study, we demonstrated for the first time the possible presence of RNAa phenomenon in the tick vector, Haemaphysalis longicornis (Asian longhorned tick). We targeted the 3'-UTR of a novel endochitinase-like gene (HlemCHT) identified previously in H. longicornis eggs for dsRNA-mediated gene activation. Our results showed an increased gene expression in eggs of H. longicornis endochitinase-dsRNA-injected (dsHlemCHT) ticks on day-13 post-oviposition. Furthermore, we observed that eggs of dsHlemCHT ticks exhibited relatively early egg development and hatching, suggesting a dsRNA-mediated activation of the HlemCHT gene in the eggs. This is the first attempt to provide evidence of RNAa in ticks. Although further studies are required to elucidate the detailed mechanism by which RNAa occurs in ticks, the outcome of this study provides new opportunities for the use of RNAa as a gene overexpression tool in future studies on tick biology, to reduce the global burden of ticks and tick-borne diseases.

Mammalian and Avian Larval Schistosomatids in Bangladesh: Molecular Characterization, Epidemiology, Molluscan Vectors, and Occurrence of Human Cercarial Dermatitis

Schistosomiasis is a neglected tropical disease (NTD) caused by blood flukes (Schistosoma spp.). Schistosomatids affect a wide array of vertebrate hosts, including humans. In the present study, multiple species of schistosomatids were identified by isolating schistosomatid cercariae (SC) from naturally infected snails. We also described different biotic and abiotic factors influencing SC infections in snails and reported human cercarial dermatitis (HCD) for the first time in Bangladesh. A total of 22,012 snails of seven species: Lymnaea auricularia, L. luteola, Indoplanorbis exustus, Physa acuta, Viviparus bengalensis, Brotia spp., and Thiara spp., were collected and examined. Among these snails, 581 (2.6%) belonging to five species: L. luteola, L. auricularia, P. acuta, I. exustus, and V. bengalensis, were infected with SC. The rate of infection was the highest for L. luteola (11.1%), followed by L. auricularia (5.3%), and was the lowest for V. bengalensis (0.4%). Prevalence in snails was the highest in September (16.8%), followed by October (9.5%) and November (8.8%), and was the lowest in colder months, such as January (1.8%) and February (2.1%). Infections with schistosomatids were more common in larger snails and snails collected from sunny areas. We confirmed the presence of Schistosoma indicum, S. incognitum, S. nasale, S. spindale, and Trichobilharzia szidati by PCR and sequencing. Through a questionnaire survey, we detected HCD in 214 (53.5%) individuals, and the infection rate was almost equally distributed across all professions. Collectively, the present results suggest that lymnaeid snails are the main vector for Schistosoma spp. prevalent in Bangladesh, and schistosomatids with zoonotic potential are also prevalent.

Ambivalent Roles of Oxidative Stress in Triangular Relationships among Arthropod Vectors, Pathogens and Hosts

Blood-feeding arthropods, particularly ticks and mosquitoes are considered the most important vectors of arthropod-borne diseases affecting humans and animals. While feeding on blood meals, arthropods are exposed to high levels of reactive oxygen species (ROS) since heme and other blood components can induce oxidative stress. Different ROS have important roles in interactions among the pathogens, vectors, and hosts. ROS influence various metabolic processes of the arthropods and some have detrimental effects. In this review, we investigate the various roles of ROS in these arthropods, including their innate immunity and the homeostasis of their microbiomes, that is, how ROS are utilized to maintain the balance between the natural microbiota and potential pathogens. We elucidate the mechanism of how ROS are utilized to fight off invading pathogens and how the arthropod-borne pathogens use the arthropods’ antioxidant mechanism to defend against these ROS attacks and their possible impact on their vector potentials or their ability to acquire and transmit pathogens. In addition, we describe the possible roles of ROS in chemical insecticide/acaricide activity and/or in the development of resistance. Overall, this underscores the importance of the antioxidant system as a potential target for the control of arthropod and arthropod-borne pathogens.

Protein profiling of hemolymph in Haemaphysalis flava ticks

Background

Tick hemolymph bathes internal organs, acts as an exchange medium for nutrients and cellular metabolites, and offers protection against pathogens. Hemolymph is abundant in proteins. However, there has been limited integrated protein analysis in tick hemolymph thus far. Moreover, there are difficulties in differentiating tick-derived proteins from the host source. The aim of this study was to profile the tick/host protein components in the hemolymph of Haemaphysalis flava.

Methods

Hemolymph from adult engorged H. flava females was collected by leg amputation from the Erinaceus europaeus host. Hemolymph proteins were extracted by a filter-aided sample preparation protocol, digested by trypsin, and assayed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). MS raw data were searched against the UniProt Erinaceidae database and H. flava protein database for host- and tick-derived protein identification. Protein abundance was further quantified by intensity-based absolute quantification (iBAQ).

Results

Proteins extracted from hemolymph unevenly varied in size with intense bands between 100 and 130 kDa. In total, 312 proteins were identified in the present study. Therein 40 proteins were identified to be host-derived proteins, of which 18 were high-confidence proteins. Top 10 abundant host-derived proteins included hemoglobin subunit-α and subunit-β, albumin, serotransferrin-like, ubiquitin-like, haptoglobin, α-1-antitrypsin-like protein, histone H2B, apolipoprotein A-I, and C3-β. In contrast, 169 were high-confidence tick-derived proteins. These proteins were classified into six categories based on reported functions in ticks, i.e., enzymes, enzyme inhibitors, transporters, immune-related proteins, muscle proteins, and heat shock proteins. The abundance of Vg, microplusin and α-2-macroglobulin was the highest among tick-derived proteins as indicated by iBAQ.

Conclusions

Numerous tick- and host-derived proteins were identified in hemolymph. The protein profile of H. flava hemolymph revealed a sophisticated protein system in the physiological processes of anticoagulation, digestion of blood meal, and innate immunity. More investigations are needed to characterize tick-derived proteins in hemolymph.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05287-7.

Host Immune Responses to Salivary Components - A Critical Facet of Tick-Host Interactions

Tick sialome is comprised of a rich cocktail of bioactive molecules that function as a tool to disarm host immunity, assist blood-feeding, and play a vibrant role in pathogen transmission. The adaptation of the tick's blood-feeding behavior has lead to the evolution of bioactive molecules in its saliva to assist them to overwhelm hosts' defense mechanisms. During a blood meal, a tick secretes different salivary molecules including vasodilators, platelet aggregation inhibitors, anticoagulants, anti-inflammatory proteins, and inhibitors of complement activation; the salivary repertoire changes to meet various needs such as tick attachment, feeding, and modulation or impairment of the local dynamic and vigorous host responses. For instance, the tick's salivary immunomodulatory and cement proteins facilitate the tick's attachment to the host to enhance prolonged blood-feeding and to modulate the host's innate and adaptive immune responses. Recent advances implemented in the field of "omics" have substantially assisted our understanding of host immune modulation and immune inhibition against the molecular dynamics of tick salivary molecules in a crosstalk between the tick-host interface. A deep understanding of the tick salivary molecules, their substantial roles in multifactorial immunological cascades, variations in secretion, and host immune responses against these molecules is necessary to control these parasites. In this article, we reviewed updated knowledge about the molecular mechanisms underlying host responses to diverse elements in tick saliva throughout tick invasion, as well as host defense strategies. In conclusion, understanding the mechanisms involved in the complex interactions between the tick salivary components and host responses is essential to decipher the host defense mechanisms against the tick evasion strategies at tick-host interface which is promising in the development of effective anti-tick vaccines and drug therapeutics.

Mast Cells and Basophils in the Defense against Ectoparasites: Efficient Degradation of Parasite Anticoagulants by the Connective Tissue Mast Cell Chymases

Ticks, lice, flees, mosquitos, leeches and vampire bats need to prevent the host's blood coagulation during their feeding process. This is primarily achieved by injecting potent anticoagulant proteins. Basophils frequently accumulate at the site of tick feeding. However, this occurs only after the second encounter with the parasite involving an adaptive immune response and IgE. To study the potential role of basophils and mast cells in the defense against ticks and other ectoparasites, we produced anticoagulant proteins from three blood-feeding animals; tick, mosquito, and leech. We tested these anticoagulant proteins for their sensitivity to inactivation by a panel of hematopoietic serine proteases. The majority of the connective tissue mast cell proteases tested, originating from humans, dogs, rats, hamsters, and opossums, efficiently cleaved these anticoagulant proteins. Interestingly, the mucosal mast cell proteases that contain closely similar cleavage specificity, had little effect on these anticoagulant proteins. Ticks have been shown to produce serpins, serine protease inhibitors, upon a blood meal that efficiently inhibit the human mast cell chymase and cathepsin G, indicating that ticks have developed a strategy to inactivate these proteases. We show here that one of these tick serpins (IRS-2) shows broad activity against the majority of the mast cell chymotryptic enzymes and the neutrophil proteases from human to opossum. However, it had no effect on the mast cell tryptases or the basophil specific protease mMCP-8. The production of anticoagulants, proteases and anti-proteases by the parasite and the host presents a fascinating example of an arms race between the blood-feeding animals and the mammalian immune system with an apparent and potent role of the connective tissue mast cell chymases in the host defense.

Transcriptomic Analysis of Salivary Glands of Ornithodoros brasiliensis Aragão, 1923, the Agent of a Neotropical Tick-Toxicosis Syndrome in Humans

Tick salivary glands produce and secrete a variety of compounds that modulate host responses and ensure a successful blood meal. Despite great progress made in the identification of ticks salivary compounds in recent years, there is still a paucity of information concerning salivary molecules of Neotropical argasid ticks. Among this group of ticks, considering the number of human cases of parasitism, including severe syndromes and hospitalization, Ornithodoros brasiliensis can be considered one of the major Neotropical argasid species with impact in public health. Here, we describe the transcriptome analysis of O. brasiliensis salivary glands (ObSG). The transcriptome yielded ~14,957 putative contigs. A total of 368 contigs were attributed to secreted proteins (SP), which represent approximately 2.5% of transcripts but ~53% expression coverage transcripts per million. Lipocalins are the major protein family among the most expressed SP, accounting for ~16% of the secretory transcripts and 51% of secretory protein abundance. The most expressed transcript is an ortholog of TSGP4 (tick salivary gland protein 4), a lipocalin first identified in Ornithodoros kalahariensis that functions as a leukotriene C₄ scavenger. A total of 55 lipocalin transcripts were identified in ObSG. Other transcripts potentially involved in tick-host interaction included as: basic/acid tail secretory proteins (second most abundant expressed group), serine protease inhibitors (including Kunitz inhibitors), 5' nucleotidases (tick apyrases), phospholipase A₂, 7 disulfide bond domain, cystatins, and tick antimicrobial peptides. Another abundant group of proteins in ObSG is metalloproteases. Analysis of these major protein groups suggests that several duplication events after speciation were responsible for the abundance of redundant compounds in tick salivary glands. A full mitochondrial genome could be assembled from the transcriptome data and confirmed the close genetic identity of the tick strain sampled in the current study, to a tick strain previously implicated in tick toxicoses. This study provides novel information on the molecular composition of ObSG, a Brazilian endemic tick associated with several human cases of parasitism. These results could be helpful in the understanding of clinical findings observed in bitten patients, and also, could provide more information on the evolution of Neotropical argasids.

Changing the Recipe: Pathogen Directed Changes in Tick Saliva Components

Ticks are obligate hematophagous parasites and are important vectors of a wide variety of pathogens. These pathogens include spirochetes in the genus Borrelia that cause Lyme disease, rickettsial pathogens, and tick-borne encephalitis virus, among others. Due to their prolonged feeding period of up to two weeks, hard ticks must counteract vertebrate host defense reactions in order to survive and reproduce. To overcome host defense mechanisms, ticks have evolved a large number of pharmacologically active molecules that are secreted in their saliva, which inhibits or modulates host immune defenses and wound healing responses upon injection into the bite site. These bioactive molecules in tick saliva can create a privileged environment in the host’s skin that tick-borne pathogens take advantage of. In fact, evidence is accumulating that tick-transmitted pathogens manipulate tick saliva composition to enhance their own survival, transmission, and evasion of host defenses. We review what is known about specific and functionally characterized tick saliva molecules in the context of tick infection with the genus Borrelia, the intracellular pathogen Anaplasma phagocytophilum, and tick-borne encephalitis virus. Additionally, we review studies analyzing sialome-level responses to pathogen challenge.

De novo assembled salivary gland transcriptome and expression pattern analyses for Rhipicephalus evertsi evertsi Neuman, 1897 male and female ticks

Ticks secrete proteins in their saliva that change over the course of feeding to modulate the host inflammation, immune responses, haemostasis or may cause paralysis. RNA next generation sequencing technologies can reveal the complex dynamics of tick salivary glands as generated from various tick life stages and/or males and females. The current study represents 15,115 Illumina sequenced contigs of the salivary gland transcriptome from male and female Rhipicephalus evertsi evertsi ticks of early, mid and late feeding stages from 1320 separate assemblies using three short read assemblers. The housekeeping functional class contributed to the majority of the composition of the transcriptome (80%) but with lower expression (51%), while the secretory protein functional class represented only 14% of the transcriptome but 46% of the total coverage. Six percent had an unknown status contributing 3% of the overall expression in the salivary glands. Platelet aggregation inhibitors, blood clotting inhibitors and immune-modulators orthologous to the ancestral tick lineages were confirmed in the transcriptome and their differential expression during feeding in both genders observed. This transcriptome contributes data of importance to salivary gland biology and blood feeding physiology of non-model organisms.

Acquired tick resistance: The trail is hot

Acquired tick resistance is a phenomenon wherein the host elicits an immune response against tick salivary components upon repeated tick infestations. The immune responses, potentially directed against critical salivary components, thwart tick feeding, and the animal becomes resistant to subsequent tick infestations. The development of tick resistance is frequently observed when ticks feed on non-natural hosts, but not on natural hosts. The molecular mechanisms that lead to the development of tick resistance are not fully understood, and both host and tick factors are invoked in this phenomenon. Advances in molecular tools to address the host and the tick are beginning to reveal new insights into this phenomenon and to uncover a deeper understanding of the fundamental biology of tick-host interactions. This review will focus on the expanding understanding of acquired tick resistance and highlight the impact of this understanding on anti-tick vaccine development efforts.

A transcriptome and proteome of the tick Rhipicephalus microplus shaped by the genetic composition of its hosts and developmental stage

The cattle tick, Rhipicephalus microplus, is a monoxenous tick that co-evolved with indicine cattle on the Indian subcontinent. It causes massive damage to livestock worldwide. Cattle breeds present heritable, contrasting phenotypes of tick loads, taurine breeds carrying higher loads of the parasite than indicine breeds. Thus, a useful model is available to analyze mechanisms that determine outcomes of parasitism. We sought to gain insights on these mechanisms and used RNA sequencing and Multidimensional Protein Identification Technology (MudPIT) to generate a transcriptome from whole larvae and salivary glands from nymphs, males and females feeding on genetically susceptible and resistant bovine hosts and their corresponding proteomes. 931,698 reads were annotated into 11,676 coding sequences (CDS), which were manually curated into 116 different protein families. Male ticks presented the most diverse armamentarium of mediators of parasitism. In addition, levels of expression of many genes encoding mediators of parasitism were significantly associated with the level and stage of host immunity and/or were temporally restricted to developmental stages of the tick. These insights should assist in developing novel, sustainable technologies for tick control.

Gene Expression in the Salivary Gland of Rhipicephalus (Boophilus) microplus Fed on Tick-Susceptible and Tick-Resistant Hosts

The success of cattle tick fixation largely depends on the secretion of substances that alter the immune response of the host. The majority of these substances are expressed by the parasite salivary gland and secreted in tick saliva. It is known that hosts can mount immune responses against ticks and bovine European breeds, and bovine industrial crossbreeds are more susceptible to infestations than are Bos indicus cattle. To identify candidates for the development of novel control strategies for the cattle tick Rhipicephalus (Boophilus) microplus, a salivary gland transcriptome analysis of engorged females fed on susceptible or resistant hosts was performed. Using RNA-Seq, transcriptomes were de novo assembled and produced a total of 235,451 contigs with 93.3% transcriptome completeness. Differential expression analysis identified 137 sequences as differentially expressed genes (DEGs) between ticks raised on tick-susceptible or tick-resistant cattle. DEGs predicted to be secreted proteins include innexins, which are transmembrane proteins that form gap junction channels; the transporters Na⁺/dicarboxylate, Na⁺/tricarboxylate, and phosphate transporter and a putative monocarboxylate transporter; a phosphoinositol 4-phosphate adaptor protein; a cysteine-rich protein containing a trypsin inhibitor-like (TIL) domain; a putative defense protein 3 containing a reeler domain; and an F-actin-uncapping protein LRRC16A with a CARMIL_C domain; these genes were upregulated in ticks fed on tick-susceptible cattle. DEGs predicted to be non-secreted proteins included a small heat shock protein and the negative elongation factor B-like, both acting in a coordinated manner to increase HSP transcript levels in the salivary glands of the ticks fed on tick-susceptible cattle; the 26S protease regulatory subunit 6B and another chaperone with similarity to calnexin, also upregulated in ticks fed on tick-susceptible cattle; an EF-hand calcium binding protein and a serine carboxypeptidase (SCP), both involved in the blood coagulation cascade and upregulated in ticks fed on tick-susceptible cattle; and two ribosomal proteins, the 60S acidic ribosomal protein P2 and the 60S ribosomal protein L19. These results help to characterize cattle tick salivary gland gene expression in tick-susceptible and tick-resistant hosts and suggest new putative targets for the control of tick infestations, as those genes involved in the mechanism of stress response during blood feeding.

Characterization of the RAGE-binding protein, Strongyloides venestatin, produced by the silkworm-baculovirus expression system

The receptor for advanced glycation end products (RAGE) recognizes Ca⁺⁺-binding proteins, such as members of the S100 protein family released by dead or devitalized tissues, and plays an important role in inflammatory responses. We recently identified the Ca⁺⁺-binding protein, venestatin, secreted from the rodent parasitic nematode, Strongyloides venezuelensis. We herein characterized recombinant venestatin, which is abundantly produced by the silkworm-baculovirus expression system (silkworm-BES), particularly in its interaction with RAGE. Venestatin from silkworm-BES possessed a binding capacity with Ca⁺⁺ ions and vaccine immunogenicity against S. venezuelensis larvae in mice, which is similar to venestatin produced by the E. coli expression system (EES). Venestatin from silkworm-BES had a higher affinity for human recombinant RAGE than that from EES, and their affinities were Ca⁺⁺-dependent. RAGE in the mouse lung co-immunoprecipitated with venestatin from silkworm-BES administered intranasally, indicating that it bound endogenous mouse RAGE. The present results suggest that venestatin from silkworm-BES affects RAGE-mediated pathological processes.

Deciphering Biological Processes at the Tick-Host Interface Opens New Strategies for Treatment of Human Diseases

Ticks are obligatory blood-feeding ectoparasites, causing blood loss and skin damage in their hosts. In addition, ticks also transmit a number of various pathogenic microorganisms that cause serious diseases in humans and animals. Ticks evolved a wide array of salivary bioactive compounds that, upon injection into the host skin, inhibit or modulate host reactions such as hemostasis, inflammation and wound healing. Modulation of the tick attachment site in the host skin involves mainly molecules which affect physiological processes orchestrated by cytokines, chemokines and growth factors. Suppressing host defense reactions is crucial for tick survival and reproduction. Furthermore, pharmacologically active compounds in tick saliva have a promising therapeutic potential for treatment of some human diseases connected with disorders in hemostasis and immune system. These disorders are often associated to alterations in signaling pathways and dysregulation or overexpression of specific cytokines which, in turn, affect mechanisms of angiogenesis, cell motility and cytoskeletal regulation. Moreover, tick salivary molecules were found to exert cytotoxic and cytolytic effects on various tumor cells and have anti-angiogenic properties. Elucidation of the mode of action of tick bioactive molecules on the regulation of cell processes in their mammalian hosts could provide new tools for understanding the complex changes leading to immune disorders and cancer. Tick bioactive molecules may also be exploited as new pharmacological inhibitors of the signaling pathways of cytokines and thus help alleviate patient discomfort and increase patient survival. We review the current knowledge about tick salivary peptides and proteins that have been identified and functionally characterized in in vitro and/or in vivo models and their therapeutic perspective.

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.

The Essential Role of Tick Salivary Glands and Saliva in Tick Feeding and Pathogen Transmission

As long-term pool feeders, ticks have developed myriad strategies to remain discreetly but solidly attached to their hosts for the duration of their blood meal. The critical biological material that dampens host defenses and facilitates the flow of blood-thus assuring adequate feeding-is tick saliva. Saliva exhibits cytolytic, vasodilator, anticoagulant, anti-inflammatory, and immunosuppressive activity. This essential fluid is secreted by the salivary glands, which also mediate several other biological functions, including secretion of cement and hygroscopic components, as well as the watery component of blood as regards hard ticks. When salivary glands are invaded by tick-borne pathogens, pathogens may be transmitted via saliva, which is injected alternately with blood uptake during the tick bite. Both salivary glands and saliva thus play a key role in transmission of pathogenic microorganisms to vertebrate hosts. During their long co-evolution with ticks and vertebrate hosts, microorganisms have indeed developed various strategies to exploit tick salivary molecules to ensure both acquisition by ticks and transmission, local infection and systemic dissemination within the vertebrate host.

Venestatin, a Ca++-binding protein from the parasitic nematode Strongyloides venezuelensis, is involved in the larval migration process

The secretory EF-hand Ca⁺⁺-binding proteins act as calcium signaling molecules for control of cell functions, but those proteins from parasitic helminths are poorly understood. Here, we have identified and characterized an EF-hand Ca⁺⁺-binding protein from the rodent nematode, Strongyloides venezuelensis, termed 'venestatin', which is highly conserved in Strongyloides spp. Canonical two EF-hand domains and a signal peptide are present in venestatin. A gel mobility shift assay and Ruthenium red staining indicated that the recombinant venestatin possesses binding ability with Ca⁺⁺ ions. Endogenous venestatin was seemingly localized in the hypodermis and gut of the worms and was found in the excretory-secretory products. Quantitative reverse transcription-PCR data showed that venestatin-specific transcript was upregulated in the parasitic stages of S. venezuelensis, and the upregulation occurred promptly after larval invasion through the host's skin, but not in the case of in vitro incubation. Immunization of mice with recombinant venestatin caused a 55% reduction in larval migration to the lungs, and lung hemorrhaging was mild compared with non-immunized groups, suggesting that anti-venestatin sera may interfere with larval migration from skin to lung. Our results suggest that venestatin is secreted from the hypodermis and gut of S. venezuelensis, and has pivotal roles in larval migration.

Partial characterization of a novel anti-inflammatory protein from salivary gland extract of Hyalomma anatolicum anatolicum 77Acari: Ixodidae) ticks

Aim:

Hyalomma anatolicum anatolicum ticks transmit Theileria annulata, causative agent of tropical theileriosis to cattle and buffaloes causing a major economic loss in terms of production and mortality in tropical countries. Ticks have evolved several immune evading strategies to circumvent hosts’ rejection and achieve engorgement. Successful feeding of ticks relies on a pharmacy of chemicals located in their complex salivary glands and secreted saliva. These chemicals in saliva could inhibit host inflammatory responses through modulating cytokine secretion and detoxifying reactive oxygen species. Therefore, the present study was aimed to characterize anti-inflammatory peptides from salivary gland extract (SGE) of H. a. anatolicum ticks with a view that this information could be utilized in raising vaccines, designing synthetic peptides or peptidomimetics which can further be developed as novel therapeutics.

Materials and Methods:

Salivary glands were dissected out from partially fed adult female H. a. anatolicum ticks and homogenized under the ice to prepare SGE. Gel filtration chromatography was performed using Sephadex G-50 column to fractionate the crude extract. Protein was estimated in each fraction and analyzed for identification of anti-inflammatory activity. Sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) was run for further characterization of protein in desired fractions.

Results:

A novel 28 kDa protein was identified in H. a. anatolicum SGE with pronounced anti-inflammatory activity.

Conclusion:

Purification and partial characterization of H. a. anatolicum SGE by size-exclusion chromatography and SDS-PAGE depicted a 28 kDa protein with prominent anti-inflammatory activity.

Enolase, a plasminogen receptor isolated from salivary gland transcriptome of the ixodid tick Haemaphysalis flava

Enolase, a multifunctional protein, is shown to act as a plasminogen receptor that contributes to fibrinolysis, which plays an important role in preventing the formation of blood clots during tick feeding. The study of enolase genes provides opportunities to develop a potential antigen target for tick control. So far, enolase has been identified in only a few species of ticks. Knowledge of the exact mechanisms of plasminogen activation and fibrinolysis by enolase as a plasminogen receptor is limited. Here, we cloned the enolase full-length complementary DNA (cDNA) from the salivary glands of Haemaphysalis flava, expressed it, and analyzed the function of the recombinant H. flava enolase. The enolase cDNA was 1988 bp in length and encoded 433 amino acid residues. It contained two domains and some highly conserved functional motifs including an assumed membrane re-association region "AAVPSGASTGI." The enolase exhibited 83.3 % amino acid similarity to that of the putative enolase of Ixodes ricinus, and 85 % to that of Ornithodoros moubata enolase. After eukaryotic expression in insect cells, Western blot analysis showed that the mouse antiserum against the hexahistidine-tagged recombinant enolase protein recognized a band of approximately 48 kDa. The recombinant enolase bound human plasminogen in a dose-dependent manner and enhanced plasminogen activation in the presence of host tissue plasminogen activator (t-PA), most probably to promote fibrinolysis and maintain blood flow at the host-tick interface. Real-time quantitative polymerase chain reaction (qPCR) analysis showed that the expression level of enolase in salivary glands was significantly higher than in other tested tissues. Although the enolase was expressed in all developmental stages, it had the highest expression in the rapid blood feeding period of ticks. These findings indicate that the enolase might play an important role in blood feeding of H. flava.

Longistatin in tick saliva blocks advanced glycation end-product receptor activation

Ticks are notorious hematophagous ectoparasites and vectors of many deadly pathogens. As an effective vector, ticks must break the strong barrier provided by the skin of their host during feeding, and their saliva contains a complex mixture of bioactive molecules that paralyze host defenses. The receptor for advanced glycation end products (RAGE) mediates immune cell activation at inflammatory sites and is constitutively and highly expressed in skin. Here, we demonstrate that longistatin secreted with saliva of the tick Haemaphysalis longicornis binds RAGE and modulates the host immune response. Similar to other RAGE ligands, longistatin specifically bound the RAGE V domain, and stimulated cultured HUVECs adhered to a longistatin-coated surface; this binding was dramatically inhibited by soluble RAGE or RAGE siRNA. Treatment of HUVECs with longistatin prior to stimulation substantially attenuated cellular oxidative stress and prevented NF-κB translocation, thereby reducing adhesion molecule and cytokine production. Recombinant longistatin inhibited RAGE-mediated migration of mouse peritoneal resident cells (mPRCs) and ameliorated inflammation in mouse footpad edema and pneumonia models. Importantly, tick bite upregulated RAGE ligands in skin, and endogenous longistatin attenuated RAGE-mediated inflammation during tick feeding. Our results suggest that longistatin is a RAGE antagonist that suppresses tick bite-associated inflammation, allowing successful blood-meal acquisition from hosts.

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.

Spit and venom from scytodes spiders: a diverse and distinct cocktail

Spiders from the family Scytodidae have a unique prey capturing technique: they spit a zig-zagged silken glue to tether prey to a surface. Effectiveness of this sticky mixture is based on a combination of contraction and adhesion, trapping prey until the spider immobilizes it by envenomation and then feeds. We identify components expressed in Scytodes thoracica venom glands using combined transcriptomic and proteomic analyses. These include homologues of toxic proteins astacin metalloproteases and potentially toxic proteins including venom allergen, longistatin, and translationally controlled tumor protein (TCTP). We classify 19 distinct groups of candidate peptide toxins; 13 of these were detected in the venom, making up 35% of the proteome. Six have significant similarity to toxins from spider species spanning mygalomorph and nonhaplogyne araneomorph lineages, suggesting their expression in venom is phylogenetically widespread. Twelve peptide toxin groups have homologues in venom gland transcriptomes of other haplogynes. Of the transcripts, approximately 50% encode glycine-rich peptides that may contribute to sticky fibers in Scytodes spit. Fifty-one percent of the identified venom proteome is a family of proteins that is homologous to sequences from Drosophila sp. and Latrodectus hesperus with uncharacterized function. Characterization of these components holds promise for discovering new functional activity.

Proteomics approach to the study of cattle tick adaptation to white tailed deer

Cattle ticks, Rhipicephalus (Boophilus) microplus, are a serious threat to animal health and production. Some ticks feed on a single host species while others such as R. microplus infest multiple hosts. White tailed deer (WTD) play a role in the maintenance and expansion of cattle tick populations. However, cattle ticks fed on WTD show lower weight and reproductive performance when compared to ticks fed on cattle, suggesting the existence of host factors that affect tick feeding and reproduction. To elucidate these factors, a proteomics approach was used to characterize tick and host proteins in R. microplus ticks fed on cattle and WTD. The results showed that R. microplus ticks fed on cattle have overrepresented tick proteins involved in blood digestion and reproduction when compared to ticks fed on WTD, while host proteins were differentially represented in ticks fed on cattle or WTD. Although a direct connection cannot be made between differentially represented tick and host proteins, these results suggested that differentially represented host proteins together with other host factors could be associated with higher R. microplus tick feeding and reproduction observed in ticks fed on cattle.

Tick salivary compounds: their role in modulation of host defences and pathogen transmission

Ticks require blood meal to complete development and reproduction. Multifunctional tick salivary glands play a pivotal role in tick feeding and transmission of pathogens. Tick salivary molecules injected into the host modulate host defence responses to the benefit of the feeding ticks. To colonize tick organs, tick-borne microorganisms must overcome several barriers, i.e., tick gut membrane, tick immunity, and moulting. Tick-borne pathogens co-evolved with their vectors and hosts and developed molecular adaptations to avoid adverse effects of tick and host defences. Large gaps exist in the knowledge of survival strategies of tick-borne microorganisms and on the molecular mechanisms of tick-host-pathogen interactions. Prior to transmission to a host, the microorganisms penetrate and multiply in tick salivary glands. As soon as the tick is attached to a host, gene expression and production of salivary molecules is upregulated, primarily to facilitate feeding and avoid tick rejection by the host. Pathogens exploit tick salivary molecules for their survival and multiplication in the vector and transmission to and establishment in the hosts. Promotion of pathogen transmission by bioactive molecules in tick saliva was described as saliva-assisted transmission (SAT). SAT candidates comprise compounds with anti-haemostatic, anti-inflammatory and immunomodulatory functions, but the molecular mechanisms by which they mediate pathogen transmission are largely unknown. To date only a few tick salivary molecules associated with specific pathogen transmission have been identified and their functions partially elucidated. Advanced molecular techniques are applied in studying tick-host-pathogen interactions and provide information on expression of vector and pathogen genes during pathogen acquisition, establishment and transmission. Understanding the molecular events on the tick-host-pathogen interface may lead to development of new strategies to control tick-borne diseases.

Bioinformatics and expression analyses of the Ixodes scapularis tick cystatin family

The cystatins are inhibitors of papain- and legumain-like cysteine proteinases, classified in MEROPS subfamilies I25A-I25C. This study shows that 84 % (42/50) of tick cystatins are putatively extracellular in subfamily I25B and the rest are putatively intracellular in subfamily I25A. On the neighbor joining phylogeny guide tree, subfamily I25A members cluster together, while subfamily I25B cystatins segregate among prostriata or metastriata ticks. Two Ixodes scapularis cystatins, AAY66864 and ISCW011771 that show 50-71 % amino acid identity to metastriata tick cystatins may be linked to pathways that are common to all ticks, while ISCW000447 100 % conserved in I. ricinus is important among prostriata ticks. Likewise metastriata tick cystatins, Dermacentor variabilis-ACF35512, Rhipicephalus microplus-ACX53850, A. americanum-AEO36092, R. sanguineus-ACX53922, D. variabilis-ACF35514, R. sanguineus-ACX54033 and A. maculatum-AEO35155 that show 73-86 % amino acid identity may be essential to metastriata tick physiology. RT-PCR expression analyses revealed that I. scapularis cystatins were constitutively expressed in the salivary glands, midguts and other tissues of unfed ticks and ticks that were fed for 24-120 h, except for ISCW017861 that are restricted to the 24 h feeding time point. On the basis of mRNA expression patterns, I. scapularis cystatins, ISCW017861, ISCW011771, ISCW002215 and ISCW0024528 that are highly expressed at 24 h are likely involved in regulating early stage tick feeding events such as tick attachment onto host skin and creation of the feeding lesion. Similarly, ISCW018602, ISCW018603 and ISCW000447 that show 2-3 fold transcript increase by 120 h of feeding are likely associated with blood meal up take, while those that maintain steady state expression levels (ISCW018600, ISCW018601 and ISCW018604) during feeding may not be associated with tick feeding regulation. We discuss our findings in the context of advancing our knowledge of tick molecular biology.

Longistatin, an EF-hand Ca2+-binding protein from vector tick: identification, purification, and characterization

EF-hand Ca(2+)-binding motif, a structural component of the EF-hand protein, functions as a calcium sensor and/or buffer in the cytosol of the cell. However, in a few exceptional cases, the EF-hand proteins are secreted from cells and play crucial roles extracellularly. We have identified longistatin, an EF-hand Ca(2+)-binding protein, from the salivary glands of the tick, Haemaphysalis longicornis. Longistatin possesses an N-terminal sequence of unknown structure and two EF-hand motifs in the C-terminus, which conserve a calmodulin-like canonical structure. Longistatin shows distinct changes in its migration during electrophoresis through SDS-PAGE gel containing calcium or ethylenediaminetetraacetic acid (EDTA). Both recombinant and endogenous forms of longistatin can be stained with rutheninum red, demonstrating that longistatin is a Ca(2+)-binding protein.

Cloning and characterization of a plasminogen-binding enolase from the saliva of the argasid tick Ornithodoros moubata

Significant amounts of enolase have recently been found in the saliva of the argasid tick Ornithodoros moubata, raising the question as to what the function of enolase in the tick-host interface is. Enolase is a multifunctional glycolytic enzyme known to act as a plasminogen receptor on cellular surfaces, promoting fibrinolysis and extracellular matrix degradation. Fibrinolysis could be important for ticks to dissolve clots that might be formed during feeding as well as to prevent clotting of the ingested blood meal in the tick midgut. Additionally, enolase-mediated extracellular matrix degradation could contribute to the tick feeding lesion. Moreover, previous observations suggested an additional antihaemostatic role for O. moubata enolase as a P-selectin antagonist ligand. Accordingly, the aim of the present study was to investigate the potential role of the O. moubata salivary enolase as a plasminogen receptor and P-selectin ligand, and to evaluate its potential as an antigen target for anti-O. moubata vaccines. The study included the cloning, sequencing and recombinant production of the O. moubata enolase, plasminogen binding and activation assays, P-selectin binding assays, animal immunization trials, and RNAi knockdown of the enolase gene. Here we confirmed that enolase is secreted to the saliva of the tick and provide convincing evidence for a role of this salivary enolase as a plasminogen receptor, most likely stimulating host fibrinolysis and maintaining blood fluidity during tick feeding. The RNAi experiments and immunization trials indicated that enolase could be also involved in the regulation of tick reproduction, suggesting new potential control strategies. Finally, the P-selectin binding experiments demonstrated that this enolase is not a P-selectin ligand.

Longistatin is an unconventional serine protease and induces protective immunity against tick infestation

Classical serine proteases use the conserved Ser/His/Asp catalytic triad to hydrolyze substrates. Here, we show that longistatin, a salivary gland protein with two EF-hand domains from the vector tick Haemaphysalis longicornis, does not have the conserved catalytic triad, but still functions as a serine protease. Longistatin was synthesized in and secreted from the salivary glands of ticks, and is injected into host tissues during the acquisition of blood-meals. Longistatin hydrolyzed fibrinogen, an essential plasma protein in the coagulation cascade, and activated plasminogen, into its active form plasmin, a serine protease that dissolves fibrin clots. Longistatin efficiently hydrolyzed several serine protease-specific substrates showing its specificity to the amide bond of Arg. Longistatin did not hydrolyze synthetic substrates specific for other groups of proteases. The enzyme was active at a wide range of temperatures and pHs, with the optimum at 37°C and pH 7. Its activity was efficiently inhibited by various serine protease inhibitors such as phenylmethanesulfonyl fluoride (PMSF), aprotinin, antipain, and leupeptin with the estimated IC(50) of 278.57 μM, 0.35 μM, 41.56 μM and 198.86 μM, respectively. In addition, longistatin was also potently inhibited by Zinc (Zn(2+)) in a concentration-dependent manner with an IC(50) value of 275 μM, and the inhibitory effect of Zn(2+) was revived by ethylenediaminetetra acetic acid (EDTA). Immunization studies revealed that longistatin sharply induced high levels of protective IgG antibodies against ticks. Immunization with longistatin reduced repletion of ticks by about 54%, post engorgement body weight by >11% and molting of nymphs by approximately 34%; thus, the vaccination trial was approximately 73% effective against tick infestation. Taken together, our results suggest that longistatin is a new potent atypical serine protease, and may be an interesting candidate for the development of anti-tick vaccines.

Longistatin, a novel plasminogen activator from vector ticks, is resistant to plasminogen activator inhibitor-1

Thrombo-occlusive diseases are major causes of morbidity and mortality, and tissue-type plasminogen activator (t-PA) is recommended for the treatment of the maladies. However, both t-PA and u-PA are rapidly inactivated by plasminogen activator inhibitor-1 (PAI-1). Here, we show that longistatin, a novel plasminogen activator isolated from the ixodid tick, Haemaphysalis longicornis is resistant to PAI-1. Longistatin was relatively less susceptible to the inhibitory effect of SDS-treated platelet lysate than physiologic PAs. Platelet lysate inhibited t-PA and tcu-PA with the IC(50) of 7.7 and 9.1 μg/ml, respectively, whereas for longistatin inhibition IC(50) was 20.1 μg/ml (p<0.01). Similarly, activated PAI-1 (20 nM) inhibited only 21.47% activity of longistatin but almost completely inhibited t-PA (99.17%) and tcu-PA (96.84%). Interestingly, longistatin retained 76.73% initial activity even after 3h of incubation with 20 nM of PAI-1. IC(50) of PAI-1 during longistatin inhibition was 88.3 nM while it was 3.9 and 3.2 nM in t-PA and tcu-PA inhibition, respectively. Longistatin completely hydrolyzed fibrin clot by activating plasminogen efficiently in the presence of 20 nM of PAI-1. Importantly, unlike t-PA, longistatin did not form complex with PAI-1. Collectively, our results suggest that longistatin is resistant to PAI-1 and maybe an interesting tool for the development of a PAI-1 resistant effective thrombolytic agent.