Tick salivary prostaglandins: Presence, origin and significance

Proteases and protease inhibitors in saliva of hard ticks: Biological role and pharmacological potential

Hard ticks (family Ixodidae) are significant vectors of pathogens affecting humans and animals. This review explores the composition of tick saliva, focusing on proteases and protease inhibitors, their biological roles, and their potential in vaccines and therapies. Tick saliva contains various proteases, mostly metalloproteases, serpins, cystatins, and Kunitz-type inhibitors, which modulate host hemostatic, immune, and wound healing responses to facilitate blood feeding and pathogen transmission. Proteases inhibit blood clotting, degrade extracellular matrix components, and modulate immune responses. Serpins, cystatins, and Kunitz-type inhibitors further inhibit key proteases involved in coagulation and inflammation, making them promising candidates for anticoagulant, anti-inflammatory, and immunomodulatory therapies. Several tick proteases and protease inhibitors have shown potential as vaccine targets, reducing tick feeding success and pathogen transmission. Future research should focus on comprehensive proteomic and genomic analyses, detailed structural and functional studies, and vaccine trials. Advanced omics approaches and bioinformatics tools will be crucial in uncovering the complex interactions between ticks, hosts, and pathogens, improving tick control strategies and public health outcomes.

Spatial Metabolomics Reveals the Multifaceted Nature of Lamprey Buccal Gland and Its Diverse Mechanisms for Blood-Feeding

Lampreys are blood-sucking vampires in marine environments. From a survival perspective, it is expected that the lamprey buccal gland exhibits a repository of pharmacologically active components to modulate the host's homeostasis, inflammatory and immune responses. By analyzing the metabolic profiles of 14 different lamprey tissues, we show that two groups of metabolites in the buccal gland of lampreys, prostaglandins and the kynurenine pathway metabolites, can be injected into the host fish to assist lamprey blood feeding. Prostaglandins are well-known blood-sucking-associated metabolites that act as vasodilators and anticoagulants to maintain vascular homeostasis and are involved in inflammatory responses. The vasomotor reactivity test on catfish aortic ring showed that kynurenine can also relax the blood vessels of the host fish, thus improving the blood flow of the host fish at the bite site. Finally, a lamprey spatial metabolomics database ( https://www.lampreydb.com ) was constructed to assist studies using lampreys as animal model.

Seroprevalence and risk factors of tropical theileriosis in smallholder asymptomatic large ruminants in Egypt

Knowledge of the prevalence and epidemiological determinants of tropical theileriosis in large ruminants, particularly in the asymptomatic carrier, is crucial for designing and implementing effective host-specific control measures. This study aimed to estimate the seroprevalence of tropical theileriosis in asymptomatic cattle and water buffaloes and identify the potential risk factors of theileriosis in large ruminants raised under smallholder-production system in Egypt. A cross-sectional study was conducted in five districts of the Sharkia governorate from March 2019 to February 2020. In total, 350 serum samples were collected from cattle and water buffaloes under smallholder-production system and tested for Theileria annulata antibodies using the indirect antibody fluorescence test (IFAT). Data on species, host characteristics, presence of ticks, season, and districts were collected at sampling using a questionnaire. A multivariable mixed-effects logistic regression model was built to determine the potential risk factors associated with T. annulate seropositivity of the animals. The overall apparent seroprevalence of T. annulata in 350 tested animals was 70%. In the univariable analyses, cattle compared to buffaloes, younger animals compared to older ones, animals with ticks on their bodies, and warmer seasons were all associated with a higher likelihood of seropositive results in the study population while sex of the animals was not associated with seropositivity. The final multivariable model showed that animals with ticks on their bodies had 3.5× higher odds of seropositivity than those with no ticks (P < 0.001), and warmer seasons were associated with the higher odds of infection compared to winter (P = 0.003). The high seroprevalence of tropical theileriosis in the study region indicates that the disease is endemic among smallholders of large ruminants. The identified risk factors of T. annulata-seropositivity in asymptomatic carrier animals provides evidence-based guidance for adopting effective intervention measures.

Tick host immunity: vector immunomodulation and acquired tick resistance

Ticks have an unparalleled ability to parasitize diverse land vertebrates. Their natural persistence and vector competence are supported by the evolution of sophisticated hematophagy and remarkable host immune-evasion activities. We analyze the immunomodulatory roles of tick saliva which facilitates their acquisition of a blood meal from natural hosts and allows pathogen transmission. We also discuss the contrasting immunological events of tick-host associations in non-reservoir or incidental hosts, in which the development of acquired tick resistance can deter tick attachment. A critical appraisal of the intricate immunobiology of tick-host associations can plant new seeds of innovative research and contribute to the development of novel preventive strategies against ticks and tick-transmitted infections.

Roles of three putative salmon louse (Lepeophtheirus salmonis) prostaglandin E2 synthases in physiology and host-parasite interactions

BACKGROUND

The salmon louse (Lepeophtheirus salmonis) is a parasite of salmonid fish. Atlantic salmon (Salmo salar) exhibit only a limited and ineffective immune response when infested with this parasite. Prostaglandins (PGs) have many biological functions in both invertebrates and vertebrates, one of which is the regulation of immune responses. This has led to the suggestion that prostaglandin E₂ (PGE₂) is important in the salmon louse host-parasite interaction, although studies of a salmon louse prostaglandin E₂ synthase (PGES) 2 gene have not enabled conformation of this hypothesis. The aim of the present study was, therefore, to characterize two additional PGES-like genes.

METHODS

Lepeophtheirus salmonis microsomal glutathione S-transferase 1 like (LsMGST1L) and LsPGES3L were investigated by sequencing, phylogenetics, transcript localization and expression studies. Moreover, the function of these putative PGES genes in addition to the previously identified LsPGES2 gene was analyzed in double stranded (ds) RNA-mediated knockdown (KD) salmon louse.

RESULTS

Analysis of the three putative LsPGES genes showed a rather constitutive transcript level throughout development from nauplius to the adult stages, and in a range of tissues, with the highest levels in the ovaries or gut. DsRNA-mediated KD of these transcripts did not produce any characteristic changes in phenotype, and KD animals displayed a normal reproductive output. The ability of the parasite to infect or modulate the immune response of the host fish was also not affected by KD.

CONCLUSIONS

Salmon louse prostaglandins may play endogenous roles in the management of reproduction and oxidative stress and may be a product of salmon louse blood digestions.

Metabolic rate and resource depletion in the tick Ixodes ricinus in response to temperature

Understanding the effects of temperature on the metabolic activity and the rate of depletion of energy reserves by Ixodes ricinus can represent an important contribution to explaining patterns of tick activity and the likely impacts of environmental change on tick and tick-borne disease risk. Here, a cohort of I. ricinus nymphs, males, and females was collected and placed into incubators at temperatures of between 5 and 30 °C. The protein, carbohydrate, total lipid, neutral lipid, and glycogen levels were measured for nymphs for up to 70 days and adults up to 42 days. In nymphs, at day 0, glycogen was the most abundant metabolite followed by carbohydrate, with relatively low concentrations of protein and lipids. For males, the concentrations of different metabolites were relatively similar. In contrast, for females, concentrations of glycogen and carbohydrate were relatively low compared to those of protein and neutral lipids. Significant exponential declines in metabolite concentrations of all metabolites were detected over time for all life-cycle stages and at all temperatures. Nymphs generally showed lower rates of resource depletion than adults at all temperatures. The lower thresholds for metabolic activity were estimated to be between -10 and -5 °C. The Q₁₀ values, which describe the thermal sensitivity of metabolic rate, were estimated to be relatively low (1.5 for nymphs, 1.71 for males, and 1.63 for females) compared to insects where they are typically around 2.5 (range: 1.5-3), and this is considered to be an adaptation to increase survival during the extended inter-feed intervals.

Dissociating effect of salivary gland extract from Ixodes ricinus on human fibroblasts: Potential impact on Borrelia transmission

Understanding the mechanism of pathogen transmission is essential for the development of strategies to reduce arthropod-borne diseases. The pharmaco- and immunomodulatory properties of insect and acarine saliva play an essential role in the efficiency of pathogen transmission. The skin as the site where arthropod saliva and pathogens are inoculated - represents the key interface in vector-borne diseases. We identified tick molecules potentially involved in pathogen transmission, using micro-HPLC and mass spectrometry, followed by in vitro assays on human skin cells. Histone H4 isolated from Ixodes ricinus salivary gland extract was identified as a molecule with a dissociating effect on human primary fibroblasts. This histone might be involved in the formation of the feeding pool formed around the tick mouthparts and responsible of tissue necrosis in the vertebrate host. Thanks to its selective antimicrobial activity, it may also sterilize the feeding pool and facilitate transmission of pathogens such as Borrelia burgdorferi sensu lato.

Immunomodulatory and morphophysiological effects of Rhipicephalus sanguineus s. l. (Acari: Ixodidae) salivary gland extracts

Rhipicephalus sanguineus s. l. is popularly known as the "brown dog tick" since dogs are its preferential hosts, but the species has been reported to parasitize other mammals, including humans, with significant medical-veterinary importance since it transmits several important pathogenic agents during the feeding period. The tick saliva is a complex mixture that has several functions, including the capability to modulate the hemostatic, inflammatory and immunologic systems of the host, allowing pathogens to settle. Despite knowledge about the immunosuppressive action of tick saliva, little is known about the mechanisms involved in this process and the morphophysiological effects caused by exposure to the salivary gland extract, taking into consideration the different periods of the glandular cycle. Thus, the objective of this study was to analyze the in vitro effects of salivary gland extracts obtained from R. sanguineus s. l. females fed on host rabbits for two (SGE2 - Salivary Gland Extracts of 2 days) and four days (SGE4 - Salivary Gland Extracts of 4 days) on J774 cells (monocyte macrophage cell line) and verify the occurrence of morphological and immunomodulatory alterations in these cells when exposed to different concentrations of these extracts. The results showed that: (i) SGE2 and SGE4 at the concentration of 4 μg/mL presented cytotoxicity to the J774 cells exposed for 24 and 48 hours; (ii) SGE2 at the concentrations of 2 μg/mL(48-hour exposure) and 1 μg/mL (24-hour exposure) and SGE4 at the concentrations of 2 and 1 μg/mL (48-hour exposure) showed proinflammatory activity, confirmed by the increased secretion of NO and proinflammatory cytokine (IL-2), and the presence of morphological characteristics detected by microscopy; and (iii) SGE2 and SGE4 at the concentrations of 0.5 and 0.1 μg/mL had immunomodulatory activity, demonstrated by decreases in the secretion of NO and proinflammatory cytokines (IL2, IL-6 and TNF-α) and increase in the synthesis of IL-10, confirmed by the morphophysiological analysis. These unprecedented data are extremely relevant for future research to identify the processes involved in the ectoparasite-host relationship, as well to develop more efficient tick control strategies.

Wonders of tick saliva

Saliva of ticks is arguably the most complex saliva of any animal. This is particularly the case for ixodid species that feed for many days firmly attached to the same skin site of their obliging host. Sequencing and spectrometry technologies combined with bioinformatics are enumerating ingredients in the saliva cocktail. The dynamic and expanding saliva recipe is helping decipher the wonderous activities of tick saliva, revealing how ticks stealthily hide from their hosts while satisfying their gluttony and sharing their individual resources. This review takes a tick perspective on the composition and functions of tick saliva, covering water balance, gasket and holdfast, control of host responses, dynamics, individuality, mate guarding, saliva-assisted transmission, and redundancy. It highlights areas sometimes overlooked - feeding aggregation and sharing of sialomes, and the contribution of salivary gland storage granules - and questions whether the huge diversity of tick saliva molecules is 'redundant' or more a reflection on the enormous adaptability wonderous saliva confers on ticks.

Thrombin inhibitor from the salivary gland of the camel tick Hyalomma dromedarii

Blood-sucking arthropods have different types of anticoagulants to allow the ingestion of a blood meal from their hosts. In this study, five anticoagulants prolonging the activated partial thromboplastin time were resolved from the salivary gland crude extract of the camel tick Hyalomma dromedarii by chromatography on diethylaminoethyl (DEAE)-cellulose column. They were designated P1, P2, P3, P4 and P5 according to their elution order. P5 was found to be a potent thrombin inhibitor and purified by ultrafiltration through two centrifugal concentrators of 50 and 30 kDa molecular weight cut-off (MWCO), respectively. The camel tick salivary gland thrombin inhibitor was purified 60.6 folds with a specific activity of 564 units/mg protein. It turned out to be homogenous on native-PAGE with molecular weight of 36 kDa as detected on 12% SDS-PAGE. It inhibits bovine thrombin competitively with K _i value of 0.55 μM. A task for the future will be the elucidation of this thrombin inhibitor structure to allow its application in thrombosis treatment.

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.

MicroRNA-275 and its target Vitellogenin-2 are crucial in ovary development and blood digestion of Haemaphysalis longicornis

Background

The hard tick Haemaphysalis longicornis is widely distributed in eastern Asia, New Zealand and Australia and is considered the major vector of Theileria and Babesia, harmful parasites to humans and animals. Female ticks need successful blood meals to complete the life-cycle. Therefore, elucidation of the underlying molecular mechanisms of H. longicornis development and reproduction is considered important for developing control strategies against the tick and tick-borne pathogens.

Methods

Luciferase assays were used to identify the targets of micro RNA miR-275 in vitro. RNAi of Vitellogenin (Vg) was used in phenotype rescue experiments of ticks with miR-275 inhibition, and these analyses were used to identify the authentic target of miR-275 in vivo. The expression of miR-275 in different tissues and developmental stages of ticks was assessed by real-time PCR. To elucidate the functions of miR-275 in female ticks, we injected a miR-275 antagomir into female ticks and observed the phenotypic changes. Statistical analyses were performed with GraphPad5 using Student’s t-test.

Results

In this study, we identified Vg-2 as an authentic target of miR-275 both in vitro and in vivo by luciferase assays and phenotype rescue experiments. miR-275 plays the regulatory role in a tissue-specific manner and differentially in developmental stages. Silencing of miR-275 resulted in blood digestion problems, substantially impaired ovary development and significantly reduced egg mass (P < 0.0001). Furthermore, RNAi silencing of Vg-2 not only impacted the blood meal uptake (P < 0.05) but also the egg mass (P < 0.05). Significant rescue was observed in miR-275 knockout ticks when RNAi was applied to Vg-2.

Conclusion

To our knowledge, this study is the first demonstration that miR-275 targets Vg-2 in H. longicornis and regulates the functions of blood digestion and ovary development. These findings improve the molecular understanding of tick development and reproduction.

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.

Vasoconstriction induced by salivary gland extracts from ixodid ticks

In their quest for blood, most haematophagous parasites secrete vasodilators in their saliva to counter the host haemostatic response of vasoconstriction. Surprisingly, salivary gland extracts from adult female Dermacentor reticulatus and Rhipicephalus appendiculatus ticks induced constriction in a rat femoral artery model; males induced vasoconstriction or vasodilation depending on the time of feeding. Based on comparative HPLC fractionation, the active compounds inducing vasoconstriction do not appear to be prostaglandins (which ticks normally use as vasodilators). Vasoconstriction may be unique to ixodid ticks, helping them control blood flow during their prolonged blood-feeding of up to 10 days or more.

Immunosuppressive effects of Amblyomma cajennense tick saliva on murine bone marrow-derived dendritic cells

Background

Dendritic cells (DCs) are professional antigen-presenting cells with vital roles in the activation of host immunity. Ticks are bloodsucking arthropods that secrete bioactive compounds with immunomodulatory properties via their saliva. It is known that some tick species modulate the biology of DCs with different intensities; however, studies on Amblyomma cajennense, the Cayenne tick, have not yet been performed, although this species is considered one of the most capable of modulating immune responses of different hosts.

Methods

Engorged female ticks were stimulated with dopamine to induce salivation, and saliva was pooled. The effects of tick saliva on the biology of dendritic cells were assessed by examining DC differentiation, maturation, migration, cellular viability, cytokine production and expression of surface markers by flow cytometry and ELISA. Competitive enzyme immunoassays (EIA) were used to measure saliva prostaglandin-E₂ (PGE₂). Statistical significance was determined by ANOVA followed by Tukey’s post-test or by the Kruskal-Wallis test with the Dunns post-test.

Results

In this work, we demonstrated that the presence of A. cajennense saliva to bone marrow cultures inhibit DC differentiation. This inhibition was not accompanied by inhibition or induction of stimulatory and co-stimulatory molecules such as MHC-II, CD40, CD80 or CD86. Immature and mature DCs that were pre-exposed to saliva showed reduced migration toward the chemokines RANTES and MIP-3β. This inhibition was associated to a reduced expression of CCR5 (the receptor for RANTES) or CCR7 (the receptor for MIP-3β) induced by the presence of saliva in the cultures. Tick saliva also inhibited IL-12p40, IL-6 and TNF-α in a concentration-dependent manner while potentiating IL-10 cytokine production by DCs stimulated with Toll-like receptor-4 ligand. Additionally, A. cajennense tick saliva inhibited the expression of CD40 and CD86 in mature DCs while potentiating the expression of PD-L1. PGE₂ was detected as one of the constituents of saliva at a concentration of ~ 80 ng/ml, and we believe that most of the results reported herein are due to the presence of PGE₂.

Conclusions

These results help to understand the tick-host interaction and demonstrate that A. cajennense ticks appear to have mechanisms for modulating host immune cells, including DCs.

In vitro effects of prostaglandin E2 on leucocytes from sticklebacks (Gasterosteus aculeatus) infected and not infected with the cestode Schistocephalus solidus

Many helminth parasites have evolved strategies to evade the immune response of their hosts, which includes immunomodulation. Prostaglandin E2 (PGE2) is one of the best-described immunomodulators in mammalian helminth parasite infections. We hypothesized that also in teleost fish anti-helminthic immune responses are regulated via PGE2. We used a model system consisting of the tapeworm Schistocephalus solidus and its host, the three-spined stickleback (Gasterosteus aculeatus), to investigate in vitro effects of PGE2 on head kidney leucocytes (HKL) derived from sticklebacks that were experimentally infected with S. solidus. PGE2 was tested alone or in combination with either S. solidus antigens or bacterial lipopolysaccharides (LPS). After in vitro culture, cell viability and changes in leucocyte subpopulations (granulocytes to lymphocytes ratios) were monitored by flow cytometry and HKL were tested for their capacity to produce reactive oxygen species (ROS) with a chemiluminescence assay. In short term (2 h) HKL cultures PGE2 did not change the total numbers of live HKL, but the production of ROS decreased significantly with high (0.1 μmol L(-1)) PGE2 concentrations. In long-term (96 h) cultures high PGE2 concentrations induced a sharp decrease of leucocytes viability, while low (0.1 pmol L(-1)) and intermediate (0.1 nmol L(-1)) concentrations of PGE2 caused elevated leucocyte viability compared to controls. This coincided with reduced ROS production in cultures with high PGE2 and elevated ROS production in cultures with low PGE2. Granulocyte to lymphocyte ratios increased with high PGE2 concentrations alone and in combination with S. solidus antigens and LPS, most prominently with HKL from S. solidus infected sticklebacks. The present study supports the hypothesis that PGE2 might be an immunomodulator in tapeworm-fish parasite-host interactions.

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.

Microarray analysis of tick-infested skin in resistant and susceptible cattle confirms the role of inflammatory pathways in immune activation and larval rejection

Tick bites promote activation of an inflammatory process that is influenced by bovine genetic composition and its history of previous exposure. Taurine and indicine breeds are known to differ on its immune response development against Rhipicephalus microplus. Nevertheless, further investigation about the complex molecular pathways involved in the development of immune response to tick infestation in cattle presenting the same genetic background is mandatory. The aim of this work was to access the early immune response triggered by R. microplus larvae attachment in previously selected resistant and susceptible animals in a bovine F2 population derived from Gyr (Bos indicus)×Holstein (Bos taurus) crosses. Microarray data analysis of RNA samples from tick infested skin was used to evaluate the gene expression at 0, 24 and 48h after R. microplus larvae attachment. Our experimental design allowed us to deeply explore the immune response related to R. microplus infestation avoiding the innate differences between these breeds. The differentially expressed genes found reveal networks and pathways that suggest a key role of lipid metabolism in inflammation control and impairment of tick infestation in resistant animals. Acute phase response also seems to be impaired in susceptible animals. These results provide new insights about early immune response against ticks and raise the possibility of using immunomodulation processes to improve and develop novel tools for tick control.

A potent anti-thrombosis peptide (vasotab TY) from horsefly salivary glands

Vasotab TY is a KGD (Lys-Gly-Asp)-containing peptide identified from salivary glands of the horsefly of Tabanus yao. We have previously reported that vasotab TY showed a strong vasodilator activity. In the present study, vasotab TY was found to inhibit platelet aggregation effectively. It completely inhibited platelet aggregation induced by adenosine diphosphate (ADP) at the concentration of 9.6μg/ml. Vasotab TY significantly reduced thrombus weight in rat arteriovenous shunt model and inhibited thrombosis in carrageenan-induced mouse tail thrombosis model in vivo. Vasotab TY competitively bound to glycoprotein IIb/IIIa (GPIIb/IIIa) with eptifibatide, a well-known KGD-containing cyclic heptapeptide containing high specificity and high affinity for GPIIb/IIIa, suggesting that it is an antagonist of the fibrinogen receptor GPIIb/IIIa on the surface of platelet. The KGD motif in vasotab TY may facilitate the binding of it to GPIIb/IIIa. Vasotab TY showed a half-life of more than 1h in vivo. It showed little side effects including little bleeding, no hemolytic activity on human blood red cells and no cytotoxicity on human keratinocyte and THP-1 cells. Combined its vasodilator and platelet inhibitory functions, vasotab TY might be an excellent candidate for the development of clinical anti-thrombosis medicines.

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.

Prostaglandin E(2) in tick saliva regulates macrophage cell migration and cytokine profile

Background

Ticks are obligate hematophagous ectoparasites that suppress the host’s immune and inflammatory responses by secreting immuno-modulatory and anti-inflammatory molecules in their saliva. In previous studies we have shown that tick salivary gland extract (SGE) and saliva from Dermacentor variabilis have distinct effects on platelet-derived growth factor (PDGF)-stimulated IC-21 macrophage and NIH3T3-L1 fibroblast migration. Since tick saliva contains a high concentration of prostaglandin E₂ (PGE₂), a potent modulator of inflammation, we used a PGE₂ receptor antagonist to evaluate the role of PGE₂ in the different migratory responses induced by saliva and its impact on macrophage cytokine profile.

Methods

Adult ticks were fed on female New Zealand white rabbits for 5-8 days. Female ticks were stimulated with dopamine/theophylline to induce salivation and saliva was pooled. Competitive enzyme immunoassays (EIA) were used to measure saliva PGE₂ content and the changes in macrophage intracellular cyclic adenosine monophosphate (cAMP) levels. The effects of tick saliva on macrophage and fibroblast migration were assessed in the absence and presence of the PGE₂ receptor antagonist, AH 6809, using blind well chamber assays. A cytokine antibody array was used to examine the effects of tick saliva on macrophage cytokine secretion. Statistical significance was determined by one-way ANOVA; Student Newman-Kuels post-test was used for multiple comparisons.

Results

The saliva-induced increase in PDGF-stimulated macrophage migration was reversed by AH 6809. The inhibition of PDGF-stimulated fibroblast migration by saliva was also antagonist-sensitive. Tick saliva induced macrophages to secrete copious amounts of PGE₂, and conditioned medium from these cells caused an AH 6809-sensitive inhibition of stimulated fibroblast migration, showing that macrophages can regulate fibroblast activity. We show that tick saliva decreased the secretion of the pro-inflammatory cytokines regulated and normal T cell expressed and secreted (RANTES/CCL5), tumor necrosis factor-alpha (TNF-α), and soluble TNF receptor I (sTNFRI) through a PGE₂-dependent mechanism mediated by cAMP. Saliva had similar effects on lipopolysaccharide (LPS) stimulated macrophages.

Conclusions

Our data show that ticks utilize salivary PGE₂ to subvert the ability of macrophages to secrete pro-inflammatory mediators and recruit fibroblasts to the feeding lesion, therefore inhibiting wound healing.

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.

Superoxide dismutases from larvae of the camel tick Hyalomma dromedarii

Three superoxide dismutases (EC 1.15.1.1) (TLSOD1, TLSOD2 and TLSOD3) were purified from larvae of the camel tick Hyalomma dromedarii by ammonium sulfate precipitation, ion exchange and gel filtration columns. SDS-PAGE revealed that the subunit molecular masses of the SODs are 40±2 kDa, 67±1.5 kDa and 45±2.6 kDa for TLSOD1, TLSOD2 and TLSOD3, respectively. TLSOD1 and TLSOD2 are monomeric proteins, while TLSOD3 isoenzyme exhibits dimeric structure with native molecular mass of 90 kDa. The pI values are estimated at pH 8.0, pH 7.2 and pH 6.6 for the three SODs which displayed pH optima at 7.6, 8.0 and 7.8, respectively. CuCl(2) and ZnCl(2) increase the activity of TLSOD2 and TLSOD3, while MnCl(2) increases the activity of TLSOD1. KCN inhibits the activity of TLSOD2 and TLSOD3, while a remarkable resistance of TLSOD1 isoenzyme was detected. TLSOD1 is suggested to be a manganese containing isoenzyme while TLSOD2 and TLSOD3 are suggested to be copper/zinc-containing isoenzymes. These results indicate the presence of three different forms of SODs in the larval stage of camel tick. This finding will contribute to our understanding of the physiology of these ectoparasites and the development of non-traditional methods to control them.

Effects of tick saliva on the migratory and invasive activity of Saos-2 osteosarcoma and MDA-MB-231 breast cancer cells

In previous studies we showed that tick saliva modulates the migratory activity of cells involved in the wound healing response. Since cell migration is a prerequisite for tumor invasion and metastasis, we examined the effects of tick saliva on the migratory and invasive activity of Saos-2 osteosarcoma and MDA-MB-231 (MB-231) breast cancer cells and the potential signaling pathways that may be affected. Saliva inhibited basal and agonist-induced Saos-2 and MB-231 migration and invasion through a matrigel-coated filter. In the Saos-2 cells, saliva suppressed epidermal growth factor (EGF)-activation of Akt/Protein Kinase B, however, only basal extracellular signal-regulated kinase (ERK) activity was affected in MB-231 cells. EGF receptor (EGFR) overexpression masked the effect of saliva on MB-231 cells, but its ability to inhibit MB-231 migration was enhanced by the EGFR inhibitor PD 168393 and MEK inhibitor U0126. Our data indicate that the mechanisms ticks have evolved to regulate the wound healing response have generalized effects on the migratory and invasive activities of metastatic cancer cells.

Ixodes scapularis saliva mitigates inflammatory cytokine secretion during Anaplasma phagocytophilum stimulation of immune cells

Background

Ixodes scapularis saliva enables the transmission of infectious agents to the mammalian host due to its immunomodulatory, anesthetic and anti-coagulant properties. However, how I. scapularis saliva influences host cytokine secretion in the presence of the obligate intracellular rickettsial pathogen Anaplasma phagocytophilum remains elusive.

Methods

Bone marrow derived macrophages (BMDMs) were stimulated with pathogen associated molecular patterns (PAMPs) and A. phagocytophilum. Cytokine secretion was measured in the presence and absence of I. scapularis saliva. Human peripheral blood mononuclear cells (PBMCs) were also stimulated with Tumor Necrosis Factor (TNF)-α in the presence and absence of I. scapularis saliva and interleukin (IL)-8 was measured.

Results

I. scapularis saliva inhibits inflammatory cytokine secretion by macrophages during stimulation of Toll-like (TLR) and Nod-like receptor (NLR) signaling pathways. The effect of I. scapularis saliva on immune cells is not restricted to murine macrophages because decreasing levels of interleukin (IL)-8 were observed after TNF-α stimulation of human peripheral blood mononuclear cells. I. scapularis saliva also mitigates pro-inflammatory cytokine response by murine macrophages during challenge with A. phagocytophilum.

Conclusions

These findings suggest that I. scapularis may inhibit inflammatory cytokine secretion during rickettsial transmission at the vector-host interface.

The BB0646 protein demonstrates lipase and haemolytic activity associated with Borrelia burgdorferi, the aetiological agent of Lyme disease

The etiological agent of Lyme disease, Borrelia burgdorferi, is transmitted by ticks of the Ixodes genus and, if untreated, can cause significant morbidity in affected individuals. Recent reports have shown that polyunsaturated fatty acids in the B. burgdorferi cell envelope are potential targets for oxidative damage, which can be lethal. How B. burgdorferi responds to this assault is not known. Herein we report evidence that bb0646 codes for a lipase that is located within the bosR operon and that has specificity for both saturated and polyunsaturated fatty acids. Specifically, strains harbouring mutated copies of the lipase, either in the form of an insertionally inactivated construct or site-directed mutations within the active site, demonstrated attenuated lipolytic and haemolytic phenotypes when compared with the isogenic parent and trans-complements. In vivo analysis showed that while the bb0646 mutant remains infectious, the spirochaetal load is significantly lower than both the isogenic parent and the complemented mutant strains. Taken together, these data demonstrate that BB0646 is a broad substrate specific lipase that contributes to lipolytic and haemolytic activity in vitro and is required for optimal B. burgdorferi infection.

Molecular characterization of novel sulfotransferases from the tick, Ixodes scapularis

Background

Ixodes scapularis, commonly known as the blacklegged or deer tick, is the main vector of Lyme disease in the United States. Recent progress in transcriptome research has uncovered hundreds of different proteins expressed in the salivary glands of hard ticks, the majority of which have no known function, and include many novel protein families. We recently identified transcripts coding for two putative cytosolic sulfotransferases in these ticks which recognized phenolic monoamines as their substrates. In this current study, we characterize the genetic expression of these two cytosolic sulfotransferases throughout the tick life cycle as well as the enzymatic properties of the corresponding recombinant proteins. Interestingly, the resultant recombinant proteins showed sulfotransferase activity against both neurotransmitters dopamine and octopamine.

Results

The two sulfotransferase genes were coded as Ixosc SULT 1 & 2 and corresponding proteins were referred as Ixosc Sult 1 and 2. Using gene-specific primers, the sulfotransferase transcripts were detected throughout the blacklegged tick life cycle, including eggs, larvae, nymphs, adult salivary glands and adult midgut. Notably, the mRNA and protein levels were altered upon feeding during both the larval and nymphal life stages. Quantitative PCR results confirm that Ixosc SULT1 was statistically increased upon blood feeding while Ixosc SULT 2 was decreased. This altered expression led us to further characterize the function of these proteins in the Ixodid tick. The sulfotransferase genes were cloned and expressed in a bacterial expression system, and purified recombinant proteins Ixosc Sult 1(R) and 2(R) showed sulfotransferase activity against neurotransmitters dopamine and octopamine as well as the common sulfotransferase substrate p-nitrophenol. Thus, dopamine- or octopamine-sulfonation may be involved in altering the biological signal for salivary secretion in I. scapularis.

Conclusions

Collectively, these results suggest that a function of Ixosc Sult 1 and Sult 2 in Ixodid tick salivary glands may include inactivation of the salivation signal via sulfonation of dopamine or octopamine.

Tick paralysis in Australia caused by Ixodes holocyclus Neumann

Ticks are obligate haematophagous ectoparasites of various animals, including humans, and are abundant in temperate and tropical zones around the world. They are the most important vectors for the pathogens causing disease in livestock and second only to mosquitoes as vectors of pathogens causing human disease. Ticks are formidable arachnids, capable of not only transmitting the pathogens involved in some infectious diseases but also of inducing allergies and causing toxicoses and paralysis, with possible fatal outcomes for the host. This review focuses on tick paralysis, the role of the Australian paralysis tick Ixodes holocyclus, and the role of toxin molecules from this species in causing paralysis in the host.

Deconstructing tick saliva: non-protein molecules with potent immunomodulatory properties

Dendritic cells (DCs) are powerful initiators of innate and adaptive immune responses. Ticks are blood-sucking ectoparasite arthropods that suppress host immunity by secreting immunomodulatory molecules in their saliva. Here, compounds present in Rhipicephalus sanguineus tick saliva with immunomodulatory effects on DC differentiation, cytokine production, and costimulatory molecule expression were identified. R. sanguineus tick saliva inhibited IL-12p40 and TNF-α while potentiating IL-10 cytokine production by bone marrow-derived DCs stimulated by Toll-like receptor-2, -4, and -9 agonists. To identify the molecules responsible for these effects, we fractionated the saliva through microcon filtration and reversed-phase HPLC and tested each fraction for DC maturation. Fractions with proven effects were analyzed by micro-HPLC tandem mass spectrometry or competition ELISA. Thus, we identified for the first time in tick saliva the purine nucleoside adenosine (concentration of ∼110 pmol/μl) as a potent anti-inflammatory salivary inhibitor of DC cytokine production. We also found prostaglandin E(2) (PGE(2) ∼100 nM) with comparable effects in modulating cytokine production by DCs. Both Ado and PGE(2) inhibited cytokine production by inducing cAMP-PKA signaling in DCs. Additionally, both Ado and PGE(2) were able to inhibit expression of CD40 in mature DCs. Finally, flow cytometry analysis revealed that PGE(2), but not Ado, is the differentiation inhibitor of bone marrow-derived DCs. The presence of non-protein molecules adenosine and PGE(2) in tick saliva indicates an important evolutionary mechanism used by ticks to subvert host immune cells and allow them to successfully complete their blood meal and life cycle.

Silencing of three Amblyomma americanum (L.) insulin-like growth factor binding protein-related proteins prevents ticks from feeding to repletion

The insulin-like growth factor (IGF) binding proteins (IGFBP) family is the regulatory arm of the IGF signaling system that control mitogenic and anabolic actions of IGF peptide hormones. This study describes cloning and biological characterization of three Amblyomma americanum (L.) (Aam) proteins that show amino-terminal sequence and secondary structure similarity to the IGFBP superfamily. The three molecules here provisionally identified as AamIGFBP-rP1 and short (S) and long (L) AamIGFBP-rP6 are expressed in multiple tick organs and are responsive to tick feeding activity with the former being upregulated and the latter being downregulated. We show that they regulate tick physiological functions that may be related to A. americanum tick feeding success as revealed by RNAi-mediated dual silencing of AamIGFBP-rP6S and AamIGFBP-rP6L or AamIGFBP-rP1 alone, which caused a reduction in blood meal size compared to the controls. Additionally, in the case of AamIGFBP-rP1 silencing, 47% of ticks died while attempting to feed and those that did survive and spontaneously detached from the host failed to lay eggs. Although AamIGFBP-rP6S and AamIGFBP-rP6L show overall identities of 49% and 59%, respectively, to Rhipicephalus microplus C protein, the identity level jumps to ~84% when the comparison is restricted to first 70 amino acids of the mature protein. Similarly, the AamIGFBP-rP1 mature protein is ~72%, 87%, 88% and 92% identical to that of Ixodes scapularis S, R. microplus, R. appendiculatus N and A. variegatum F, respectively. The observed across-tick-species conservation suggests that the three molecules (AamIGFBP-rP1, AamIGFBP-rP6S and AamIGFBP-rP6L) represent target for development of vaccines to protect animals against multiple tick species. The data are discussed with reference to advances in tick molecular biology and the potential of the three proteins as targets for immunizing animals against tick feeding.

Expression of intracellular calcium signalling genes in cattle skin during tick infestation

It is widely acknowledged that changes in intracellular calcium ion (Ca(2+)) concentration provide dynamic signals that control a plethora of cellular processes, including triggering and mediating host defence mechanisms. In this study, quantitative real-time PCR was used to analyse gene expression of 14 Ca(2+) signalling proteins in skin obtained from high tick-resistant (HR) and low tick-resistant (LR) cattle following artificial challenge with cattle tick (Rhipicephalus (Boophilus) microplus). Up-regulation of numerous genes was observed in both HR and LR skin following tick challenge, however substantially higher transcription activation was found in HR tissue. The elevated expression in HR skin of specific Ca(2+) signalling genes such as AHNAK, CASQ, IL2, NFAT2CIP and PLCG1 may be related to host resistance. Our data suggest that Ca(2+) and its associated proteins might play an important role in host response to ticks and that further investigation is warranted.

An ion-channel modulator from the saliva of the brown ear tick has a highly modified Kunitz/BPTI structure

Ra-KLP, a 75 amino acid protein secreted by the salivary gland of the brown ear tick Rhipicephalus appendiculatus has a sequence resembling those of Kunitz/BPTI proteins. We report the detection, purification and characterization of the function of Ra-KLP. In addition, determination of the three-dimensional crystal structure of Ra-KLP at 1.6 A resolution using sulphur single-wavelength anomalous dispersion reveals that much of the loop structure of classical Kunitz domains, including the protruding protease-binding loop, has been replaced by beta-strands. Even more unusually, the N-terminal portion of the polypeptide chain is pinned to the "Kunitz head" by two disulphide bridges not found in classical Kunitz/BPTI proteins. The disulphide bond pattern has been further altered by the loss of the bridge that normally stabilizes the protease-binding loop. Consistent with the conversion of this loop into a beta-strand, Ra-KLP shows no significant anti-protease activity; however, it activates maxiK channels in an in vitro system, suggesting a potential mechanism for regulating host blood supply during feeding.

[Expression and enzymatic activity of glutathione s-transferase in tissues of Boophilus microplus females]

Cellular detoxification and excretion enzymes are important to the maintenance of cellular homeostasis. In this work mRNA transcription, protein expression and enzymatic activity of Glutathione S-transferases (GSTs), enzymes involved in the excretion of endo and xenobiotic compounds were analyzed. These parameters are elements believed to protect cells against chemical toxicity and oxidative stress in different tissues (salivary gland, ovary and synganglion) from partially engorged females and engorged females of Boophilus microplus. The results presented showed elevated GST activity in partially engorged females. The enzymatic activity decreased during the preoviposition period in engorged females. GST mRNA transcription was detected in salivary glands and synganglion from partially engorged and engorged females, but not in ovary. The results of this work help to elucidate the role of GST in tick development and assist in the understanding of the importance of GST in tick females during the preparation for oviposition.

The role of saliva in tick feeding

When attempting to feed on their hosts, ticks face the problem of host hemostasis (the vertebrate mechanisms that prevent blood loss), inflammation (that can produce itching or pain and thus initiate defensive behavior on their hosts) and adaptive immunity (by way of both cellular and humoral responses). Against these barriers, ticks evolved a complex and sophisticated pharmacological armamentarium, consisting of bioactive lipids and proteins, to assist blood feeding. Recent progress in transcriptome research has uncovered that hard ticks have hundreds of different proteins expressed in their salivary glands, the majority of which have no known function, and include many novel protein families (e.g., their primary structure is unique to ticks). This review will address the vertebrate mechanisms of these barriers as a guide to identify the possible targets of these large numbers of known salivary proteins with unknown function. We additionally provide a supplemental Table that catalogues over 3,500 putative salivary proteins from various tick species, which might assist the scientific community in the process of functional identification of these unique proteins. This supplemental file is accessble fromhttp://exon.niaid.nih.gov/transcriptome/tick_review/Sup-Table-1.xls.gz.

Molecular and biological characterization of the Amblyomma americanum organic anion transporter polypeptide

The organic anion transporting polypeptides (Oatps in rodents and other organism; OATPs in human) are Na+-independent transporters that shuttle a wide range of endogenous and xenobotic amphipathic compounds across plasma membranes. We previously discovered an Amblyomma americanumtick (Aam) Oatp cDNA among genes that were upregulated or induced in ticks that were stimulated to start feeding. In this study, we have characterized a 2860 bp full-length cDNA that encode a 724 amino acid putative protein. Bioinformatics and hydropathy analyses revealed that, in addition to the kazal-type serine proteinase inhibitor motif, AamOatp possess typical features that characterize the Oatp/OATP protein family, including 12 transmembrane (TM) domains, the consensus amino acid motif D-X-RW-(I,V)-GAWW-X-G-(F,L)-L and 11 consensus cysteine residues in the large extracellular domain between TM9 and TM10. AamOatp is constitutively and ubiquitously expressed, as determined by RT-PCR amplification of the transcript, in all organs of ticks that fed for 1–7 days. Analysis of the normalized transcript abundance revealed that from days 1 to 5 of feeding, AamOatp mRNA expression in the midgut (MG) was 60–80-fold higher than levels found in the salivary gland (SG), ovary (OV) and carcass(CA). By contrast, by day 7 of feeding, the AamOatp mRNA was 60–80-fold more strongly expressed in the OV than in the SG, MG and CA. These data strongly indicate that changing physiological needs during the tick feeding process influences transcriptional regulation of AamOatp. Our data also show that RNAi-mediated suppression of the AamOatp caused ticks to obtain smaller blood meals, which consequently resulted in ticks laying fewer eggs. The results are discussed in the context of AamOatp as a potential pharmacological or anti-tick vaccine target.

Prostaglandin E2 modulates the expression of antimicrobial peptides in the fat body and midgut of Anopheles albimanus

Prostaglandins (PGs) participate in the regulation of vertebrate and in at least six insect orders' immune responses. We identified PGE2 in midgut, fat body, Malpighian tubules, and ovarioles of Anopheles albimanus (Aa) mosquitoes. Our data indicate that PGE2 synthesis in cultured midguts responds to the presence of two bacterial species, Micrococcus luteus and Klebsiella pneumoniae. The production of mRNA coding for antimicrobial peptides Aa-Attacin, Aa-Cecropin, and Aa-Gambicin was observed in cultured fat bodies and midguts. The production of these messengers was reduced in the presence of dexamethasone, and this effect was reversed by arachidonic acid. Adding PGE2 to cultures resulted in increased Aa-cecropin mRNA and decreased Aa-attacin and Aa-gambicin mRNAs.

Prostaglandin E2 is a major inhibitor of dendritic cell maturation and function in Ixodes scapularis saliva

Tick saliva is thought to contain a number of molecules that prevent host immune and inflammatory responses. In this study, the effects of Ixodes scapularis saliva on cytokine production by bone marrow-derived dendritic cells (DCs) from C57BL/6 mice stimulated by TLR-2, TLR-4, and TLR-9 ligands were studied. Saliva at remarkably diluted concentrations (<1/2000) promotes a dose-dependent inhibition of IL-12 and TNF-alpha production induced by all TLR ligands used. Using a combination of fractionation techniques (microcon filtration, molecular sieving, and reversed-phase chromatography), we unambiguously identified PGE(2) as the salivary inhibitor of IL-12 and TNF-alpha production by DCs. Moreover, we have found that I. scapularis saliva (dilution 1/200; approximately 10 nM PGE(2)) marginally inhibited LPS-induced CD40, but not CD80, CD86, or MHC class II expression. In addition, saliva significantly suppressed the ability of DCs to stimulate Ag-specific CD4(+) T cell proliferation and IL-2 production. Notably, the effect of saliva on DC maturation and function was reproduced by comparable concentrations of standard PGE(2). These findings indicate that PGE(2) accounts for most inhibition of DC function observed with saliva in vitro. The role of salivary PGE(2) in vector-host interaction and host immune modulation and inflammation in vivo is also discussed. This study is the first to identify molecularly a DC inhibitor from blood-sucking arthropods.

Gluttony and sex in female ixodid ticks: how do they compare to other blood-sucking arthropods?

The central issue dealt with here is the role of copulation in the control of feeding behaviour in ticks and some haematophagous insects. Female ticks of the family Ixodidae normally engorge to approximately 100 x their unfed body weight, and then drop from the host, produce and lay eggs, and die. Virgins, on the other hand, normally do not exceed 5-40% (depending on species) of the normal engorged body weight. But instead of detaching voluntarily at that point most virgins remain fixed to the host for extended periods, waiting for males to find them so they can complete engorgement. Virgin haematophagous insects, and virgin ticks of the family Argasidae display little, if any, reduction in blood meal size compared to mated females, at least not during the first ovarian cycle. During subsequent ovarian cycles, meal size in some virgin insects may be somewhat reduced depending on how many eggs are retained in the reproductive tract, but the reduction is not nearly to the same extent as that observed for virgin ixodid females. The stimulatory effect of copulation on engorgement in the latter is caused by a pair of proteins (voraxin alpha and beta) produced in the testis and transferred to the female with the spermatophore. Here, I propose why it might be adaptive for an ixodid female to remain small until mated. The hypothesis is suggested from the facts that ixodid ticks remain attached to the host for days (rather than minutes), and that virgin ticks, above a certain critical weight, lose all opportunity for producing viable offspring should they be groomed off the host prematurely, or should the host die while ticks are still attached.

The Effects of Salivary Gland Extracts from Boophilus microplus Ticks on Mitogen-stimulated Bovine Lymphocytes

The effect of salivary gland extract (SGE) from the tick Boophilus microplus was examined in mitogen-stimulated lymphocytes in vitro. SGE was added to lymphocytes of seven cattle together with the mitogens concanavalin A (ConA), phytohaemagglutinin (PHA) and pokeweed mitogen (PWM). Semi-purified B cells from another seven cattle were stimulated with the mitogen lipopolysaccharide (LPS). PHA and ConA stimulated proliferation of lymphocytes to the same extent, but the inhibition due to SGE of Boophilus microplus on the proliferative response stimulated by PHA (39.0% +/- 9.3%) was less than the inhibition of proliferative response stimulated by ConA (75.4% +/- 6.9%). In contrast, SGE of B. microplus stimulated the proliferation of B cells in the presence of LPS in a dose-dependent manner. Enhanced stimulation of B cells by SGE at >4 microg in culture was greater than twice that observed when B cells were stimulated by LPS alone. SGE does not have a direct suppressive effect on bovine B cell proliferation; however, in vivo the effectiveness of B cell responses might be influenced by other immune factors, such as cytokine profiles.

Vasotab, a vasoactive peptide from horse fly Hybomitra bimaculata (Diptera, Tabanidae) salivary glands

Horse flies feed from superficial haematomas and probably rely heavily on the pharmacological properties of their saliva to find blood. Here we describe the first evidence of vasodilators in horse fly Hybomitra bimaculata (Diptera, Tabanidae) salivary gland extract and clone and express one of the active peptides (termed vasotab). Physiological tests using crude salivary gland extracts and reverse-phase HPLC fractions demonstrated positive inotropism in isolated rat hearts, vasodilatation of coronary and peripheral vessels, and Na, K-ATPase inhibition. One of the vasoactive fractions was analysed by N-terminal Edman degradation and a 47-amino-acid sequence obtained. A full-length cDNA encoding the peptide was cloned from a phage library using degenerate primer PCR and the peptide expressed in insect cells. A 20-amino-acid signal sequence precedes the mature 56-amino-acid vasotab peptide, which is a member of the Kazal-type protease inhibitor family. The peptide has a unique 7-amino-acid insertion between the third and fourth cysteine residues. The recombinant peptide prolonged the action potential and caused positive inotropism of isolated rat heart myocytes, and may be an ion channel modulator.

Tick salivary glands: function, physiology and future

The salivary glands are the organs of osmoregulation in ticks and, as such, are critical to the biological success of ticks both during the extended period off the host and also during the feeding period on the host. Absorption of water vapour from unsaturated air into hygroscopic fluid produced by the salivary glands permit the tick to remain hydrated and viable during the many months between blood-meals. When feeding, the tick is able to return about 70% of the fluid and ion content of the blood-meal into the host by salivation into the feeding site. This saliva also contains many bioactive protein and lipid components that aid acquisition of the blood-meal. The salivary glands are the site of pathogen development and the saliva the route of transmission. The importance of the multifunctional salivary glands to tick survival and vector competency makes the glands a potential target for intervention. Here we review the cell biology of tick salivary glands and discuss the application of new approaches such as expressed sequence tag projects and RNA interference to this important area in the field of tick and tick-borne pathogen research.

Tick immunobiology

Ticks are of vast medical and veterinary public health importance due to direct damage caused by feeding and their roles in transmitting well known and emerging infectious agents. Ticks and tick-borne pathogens stimulate the immune system of the host. Those immune interactions are of importance in tick biology, pathogen transmission and control of ticks and tick-borne diseases. Both innate and specific acquired immune defenses are involved in the responses of vertebrate hosts to infestation. Ticks have evolved countermeasures to circumvent host immune defenses. This review addresses the immunobiology of the tick-host interface from the perspectives of the pharmacology of tick saliva; relationship of tick saliva to pathogen transmission; host immune responses to infestation; tick modulation of host immune defences; and genomic/proteomic strategies for studying tick salivary gland molecules.

Antihemostatic Molecules from Saliva of Blood-Feeding Arthropods

The ability to feed on vertebrate blood has evolved many times in various arthropod clades. Each time this trait evolves, novel solutions to the problem posed by vertebrate hemostasis are generated. Consequently, saliva of blood-feeding arthropods has proven to be a rich source of antihemostatic molecules. Vasodilators include nitrophorins (nitric oxide storage and transport heme proteins), a variety of peptides that mimic endogenous vasodilatory neuropeptides, and proteins that catabolize or sequester endogenous vasoconstrictors. A variety of platelet aggregation inhibitors antagonize platelet responses to wound-generated signals, including ADP, thrombin, and collagen. Anticoagulants disrupt elements of both the intrinsic and extrinsic pathways. Molecular approaches (termed 'sialomics') to characterize the full inventory of mRNAs transcribed in salivary glands have revealed a surprising level of complexity within a single species. Multiple salivary proteins may be directed against each component of hemostasis, resulting in both redundancy and in some cases cooperative interactions between antihemostatic proteins, as in the case of the Rhodnius prolixus apyrase (which hydrolyzes ADP) and Rhodnius platelet aggregation inhibitor 1 (which sequesters ADP). The complexity and redundancy of saliva ensures an efficient blood meal for the arthropod, but it also provides a diverse array of novel antihemostatic molecules for the pharmacologist.

Relationship between glutathione S-transferase, catalase, oxygen consumption, lipid peroxidation and oxidative stress in eggs and larvae of Boophilus microplus (Acarina: Ixodidae)

Glutathione S-transferases (GSTs) are enzymes that act in excretion of physiologic and xenobiotic substances, protecting cells against chemical toxicity and stress. In this work, we characterized the enzymatic activity of GST in eggs and larvae of cattle tick Boophilus microplus, on different days after oviposition and eclosion. The results showed that the GST activity varied depending on the time elapsed after oviposition and eclosion. Molecules involved in mechanism of protection from oxidative stress are correlated with the increase in GST activity. The oxygen consumption kinetics showed a positive correlation with the increase in GST activity during embryogenesis. A high content of thiobarbituric acid reactive substances were observed in egg and larva extracts, indicating that ticks face high oxidative stress during embryogenesis and aging. In eggs and larvae, GST activity can be correlated to kinetic parameters of oxidative stress such as catalase and glutathione. In addition, GST activity showed strong positive correlation with lipid peroxidation, an indication that it plays a role in oxidant defences in eggs.