Protease-bound structure of Ricistatin provides insights into the mechanism of action of tick salivary cystatins in the vertebrate host

Tick saliva injected into the vertebrate host contains bioactive anti-proteolytic proteins from the cystatin family; however, the molecular basis of their unusual biochemical and physiological properties, distinct from those of host homologs, is unknown. Here, we present Ricistatin, a novel secreted cystatin identified in the salivary gland transcriptome of Ixodes ricinus ticks. Recombinant Ricistatin inhibited host-derived cysteine cathepsins and preferentially targeted endopeptidases, while having only limited impact on proteolysis driven by exopeptidases. Determination of the crystal structure of Ricistatin in complex with a cysteine cathepsin together with characterization of structural determinants in the Ricistatin binding site explained its restricted specificity. Furthermore, Ricistatin was potently immunosuppressive and anti-inflammatory, reducing levels of pro-inflammatory cytokines IL-6, IL-1β, and TNF-α and nitric oxide in macrophages; IL-2 and IL-9 levels in Th9 cells; and OVA antigen-induced CD4+ T cell proliferation and neutrophil migration. This work highlights the immunotherapeutic potential of Ricistatin and, for the first time, provides structural insights into the unique narrow selectivity of tick salivary cystatins determining their bioactivity.

A transwell assay method to evaluate Borrelia burgdorferi sensu stricto migratory chemoattraction toward tick saliva proteins

We developed a transwell assay to quantify migration of the Lyme disease agent, Borrelia burgdorferi sensu stricto (s.s.), toward Ixodes scapularis salivary gland proteins. The assay was designed to assess B. burgdorferi s.s. migration upward against gravity through a transwell polycarbonate membrane overlaid with 6% gelatin. Borreliae that channeled into the upper transwell chamber in response to test proteins were enumerated by flow cytometry. The transwell assay measured chemoattractant activity for B. burgdorferi s.s. from salivary gland extract (SGE) harvested from nymphal ticks during bloodmeal engorgement on mice 42 h post-attachment and saliva collected from adult ticks. Additionally, SGE protein fractions separated by size exclusion chromatography demonstrated various levels of chemoattractant activity in the transwell assay. Sialostatin L, and Salp-like proteins 9 and 11 were identified by mass spectrometry in SGE fractions that exhibited elevated activity. Recombinant forms of these proteins were tested in the transwell assay and showed positive chemoattractant properties compared to controls and another tick protein, S15A. These results were reproducible providing evidence that the transwell assay is a useful method for continuing investigations to find tick saliva components instrumental in driving B. burgdorferi s.s. chemotaxis.

Spatial distribution of alpha-gal in Ixodes ricinus - A histological study

Alpha-gal syndrome is a complex allergic disease in humans that is caused by specific IgE (sIgE) against the carbohydrate galactose-α-1,3-galactose (alpha-gal). Tick saliva contains alpha-gal, and tick bites are considered a major cause of the induction of alpha-gal-sIgE. The origin of alpha-gal in tick saliva remains unclarified. The presence of alpha-gal in tick tissue was visualized in this study to provide an overview of the spatial distribution of alpha-gal and to further elucidate the origin of alpha-gal in tick saliva. Fed and unfed Ixodes ricinus females were examined by histology, immunohistochemistry, immunofluorescence, transmission electron microscopy and immunoelectron microscopy using the alpha-gal-specific monoclonal antibody M86 and Marasmius oreades agglutinin (MOA) lectin. Alpha-gal epitopes were detected in the midgut, hemolymph and salivary glands, and the immunofluorescence analysis revealed signs of the endocytosis of alpha-gal-containing constituents during the process of hematophagy. Alpha-gal epitopes in endosomes of the digestive gut cells of the ticks were observed via immunoelectron microscopy. Alpha-gal epitopes were detected in dried droplets of hemolymph from unfed ticks. Intense staining of alpha-gal epitopes was found in type II granular acini of the salivary glands of fed and unfed ticks. Our data suggest that alpha-gal is not ubiquitously expressed in tick tissue but is present in both fed and unfed ticks. The findings also indicate that both the metabolic incorporation of constituents from a mammalian blood meal and endogenous production contribute to the presence of alpha-gal epitopes in ticks.

Whole animal matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry of ticks - Are spectra of Ixodes ricinus nymphs influenced by environmental, spatial, and temporal factors?

In the recent years matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) has become a useful tool to characterize arthropod species and their different stages of development. It was reported for sand flies and mosquitoes at immature stages and also assumed for ticks that geographic location can have a subtle influence on MALDI-TOF mass spectra which allows the discrimination of animals with specific local variations of the MALDI-TOF MS phenotype. It is so far uncertain, however, if these mass-spectrometric differences are based on genetic variation or on spectral features which depend on environmental or temporal features. The aim of this study was to analyze the influence of the geographic location, environmental factors and the season of the year on the MALDI-TOF mass spectra of Ixodes (I.) ricinus nymphs and if spectral variation would allow to draw conclusions with respect to the tick’s provenience or conditions that influence the tick life cycle. Application of multivariate statistical models on spectra of ticks collected in different seasons and different habitats and locations within Germany showed that the impact of the location seemed to be small while season and habitat seemed to have stronger impact on the MALDI-TOF mass spectra. Possibilities and limitations of MALDI-TOF mass spectra to draw conclusions on the tick life cycle are discussed.

Antiplasmodial activity of tick defensins in a mouse model of malaria

Malaria is a mosquito-borne disease affecting millions of people mainly in Sub-Saharan Africa, Asia and some South American countries. Drug resistance to first-line antimalarial drugs (e.g. chloroquine, sulfadoxine-pyrimethamine and artemisinin) is a major constrain in malaria control. Antimicrobial peptides (AMPs) have shown promising results in controlling Plasmodium spp. parasitemia in in vitro and in vivo models of infection. Defensins are AMPs that act primarily by disrupting the integrity of cell membranes of invasive microbes. We previously showed that defensins from the tick Ixodes ricinus inhibited significantly the growth of P. falciparum in vitro, a property that was conserved during evolution. Here, we tested the activity of three I. ricinus defensins against P. chabaudi in mice. A single dose of defensin (120 μl of 1 mg/ml solution) was administered intravenously to P. chabaudi-infected mice, and the parasitemia was followed for 24 h post-treatment. Defensin treatment inhibited significantly the replication (measured as increases in parasitemia) of P. chabaudi after 1 h and 12 h of treatment. Furthermore, defensin injection was not associated with toxicity. These results agreed with the previous report of antiplasmodial activity of tick defensins against P. falciparum in vitro and justify further studies for the use of tick defensins to control malaria.

Penthalaris, a novel recombinant five-Kunitz tissue factor pathway inhibitor (TFPI) from the salivary gland of the tick vector of Lyme disease, Ixodes scapularis

Tick saliva is a rich source of molecules with antiinflammatory, antihemostatic and immunosupressive properties. In this paper, a novel tick salivary gland cDNA with sequence homology to tissue factor pathway inhibitor (TFPI) and coding for a protein called Penthalaris has been characterized from the Lyme disease vector, Ixodes scapularis. Penthalaris is structurally unique and distinct from TFPI or TFPI-like molecules described so far, including Ixolaris, NAPc2, TFPI-1 and TFPI-2. Penthalaris is a 308-amino-acid protein (35 kDa, pI 8.58) with 12 cysteine bridges and 5 tandem Kunitz domains. Recombinant Penthalaris was expressed in insect cells and shown to inhibit factor VIIa (FVIIa)/tissue factor(TF)-induced factor X (FX) activation with an IC50 of ∼ 100 pM. Penthalaris tightly binds both zymogen FX and enzyme FXa (exosite), but not FVIIa, as demonstrated by column gel-filtration chromatography. At high concentrations, Penthalaris attenuates FVIIa/TF-induced chromogenic substrate (S2288) hydrolysis and FIX activation. In the presence of DEGR-FX or DEGR-FXa, but not des-Gla-DEGR-FXa as scaffolds, tight and stoichiometric inhibition of FVIIa/TF was achieved. In addition, Penthalaris blocks cell surface-mediated FXa generation by monomer (de-encrypted), but not dimer (encrypted) TF in HL-60 cells. Penthalaris may act in concert with Ixolaris and other salivary anti-hemostatics in order to help ticks to successfully feed on blood. Penthalaris is a novel anticoagulant and a tool to study FVIIa/TF-initiated biologic processes.

Seasonal changes in the fatty acid profile of the tick Ixodes ricinus (Acari, Ixodidae)

Fatty acids (FAs) from nymphs, females and males of Ixodes ricinus were analysed by gas chromatography/mass spectrometry. Ticks were collected from May to October 2013. The most abundant FAs were 18:1, 18:0, 16:0 and 18:2 which are also dominant FAs of insects. Adults contained higher concentrations of FAs in general than nymphs because they contain more fat body and probably a thicker layer of epicuticular lipids. Larger quantities of FAs > 20 carbon atoms in the carboxylic chain were present in females, which generally show higher content of lipids essential for oogenesis, whereas there were similar amounts of 14-18 in both sexes. In September and October, ticks contained large concentrations of the majority of FAs except for 18:1, the most abundant one in ticks collected from May through August. Thus, most FAs, especially those with more than 20 C atoms, tend to increase at lower temperatures.

Evidence of female sex pheromones and characterization of the cuticular lipids of unfed, adult male versus female blacklegged ticks, Ixodes scapularis

Copulation in Ixodes scapularis involves physical contact between the male and female (on or off the host), male mounting of the female, insertion/maintenance of the male chelicerae in the female genital pore (initiates spermatophore production), and the transfer of the spermatophore by the male into the female genital pore. Bioassays determined that male mounting behavior/chelicerae insertion required direct contact with the female likely requiring non-volatile chemical cues with no evidence of a female volatile sex pheromone to attract males. Unfed virgin adult females and replete mated adult females elicited the highest rates of male chelicerae insertion with part fed virgin adult females exhibiting a much lower response. Whole body surface hexane extracts of unfed virgin adult females and males, separately analyzed by GC-MS, identified a number of novel tick surface associated compounds: fatty alcohols (1-hexadecanol and 1-heptanol), a fatty amide (erucylamid), aromatic hydrocarbons, a short chain alkene (1-heptene), and a carboxylic acid ester (5β-androstane). These compounds are discussed in terms of their potential role in female-male communication. The two most abundant fatty acid esters found were butyl palmitate and butyl stearate present in ratios that were sex specific. Only 6 n-saturated hydrocarbons were identified in I. scapularis ranging from 10 to 18 carbons.

[THE HIGHLY EFFECTIVE DETECTION OF DNA RICKETTSIA USING TECHNIQUE OF POLYMERASE CHAIN REACTION IN REAL-TIME]

The article considers development of highly effective technique of detection of genetic material of ricketsia based on polymerase chain reaction in real-time using original primers to the most conservative sites of gene of citrate synthase (gItA). The analytical sensitivity of the developed polymerase chain reaction in real-time test permits to detect from 80 genome equivalents in analyzed sample during three hours. The high specificity of test-system is substantiated by detection of nucleotide sequences of amplificated fragments of gene gltA. The approbation ofthe polymerase chain reaction in real-time test is carried out on collection of 310 ticks of species I. persulcatus, I. pavlovskyi, D. reticulatus. It is demonstrated that the developed alternate ofprimers and probe permits with high degree of sensitivity and specifcity to detect DNA of different species of ricketsia widespread on territory of Russia (R. sibirica, R. raoultii, R. helvetica, R. tarasevichiae). The proposed polymerase chain reaction in real-time test can be appliedfor isolation of fragment of gene gltA with purpose for detecting nucleotide sequence and subsequent genetic typing of ricketsia. The application ofthe proposed technique can facilitate task of monitoring hot spots of ricketsiosis.

An investigation of binding ability of Ixodes persulcatus Schulze Salp15 with Lyme disease spirochetes

Salp15, a 15-kDa tick salivary gland protein, has several suppressive modes of activity against host immunity and plays a critical role in the transmission of Lyme disease spirochetes in Ixodes scapularis and Ixodes ricinus, major vectors of Lyme disease in North America and Western Europe. Salp15 adheres to Borrelia burgdorferi and specifically interacts with its outer surface protein C (OspC), protecting the spirochete from antibody-mediated cytotoxicity and facilitating infection in the mice. Recently, we identified two Salp15 homologues, IperSalp15-1 and IperSalp15-2, in Ixodes persulcatus, a vector for Lyme disease in Japan. Here we describe the function of IperSalp15 in the transmission of Lyme borreliosis. To investigate the function of IperSalp15, recombinant IperSalp15-1 and IperSalp15-2 were prepared in bacterial and insect cells. Both were identified in the sera of tick-immunized hamsters, indicating that these are secretory proteins in exposed host animals. Solid-phase overlay and indirect fluorescence assays showed that IperSalp15 binds to OspC from B. burgdorferi, Borrelia garinii, and Borrelia afzelii. Importantly, this binding likely protected the spirochete from antibody-mediated cytotoxicity in vitro. In addition, IperSalp15 tended to facilitate infection in mice. Thus, further characterization of tick molecules, including IperSalp15, could lead to the development of new strategies to prevent the transmission of tick-borne diseases.

Antivirulence properties of an antifreeze protein

As microbial drug-resistance increases, there is a critical need for new classes of compounds to combat infectious diseases. The Ixodes scapularis tick antifreeze glycoprotein, IAFGP, functions as an antivirulence agent against diverse bacteria, including methicillin-resistant Staphylococcus aureus. Recombinant IAFGP and a peptide, P1, derived from this protein bind to microbes and alter biofilm formation. Transgenic iafgp-expressing flies and mice challenged with bacteria, as well as wild-type animals administered P1, were resistant to infection, septic shock, or biofilm development on implanted catheter tubing. These data show that an antifreeze protein facilitates host control of bacterial infections and suggest therapeutic strategies for countering pathogens.

Molecular characterization of tick salivary gland glutaminyl cyclase

Glutaminyl cyclase (QC) catalyzes the cyclization of N-terminal glutamine residues into pyroglutamate. This post-translational modification extends the half-life of peptides and, in some cases, is essential in binding to their cognate receptor. Due to its potential role in the post-translational modification of tick neuropeptides, we report the molecular, biochemical and physiological characterization of salivary gland QC during the prolonged blood feeding of the black-legged tick (Ixodes scapularis) and the gulf-coast tick (Amblyomma maculatum). QC sequences from I. scapularis and A. maculatum showed a high degree of amino acid identity to each other and other arthropods and residues critical for zinc binding/catalysis (D159, E202, and H330) or intermediate stabilization (E201, W207, D248, D305, F325, and W329) are conserved. Analysis of QC transcriptional gene expression kinetics depicts an upregulation during the bloodmeal of adult female ticks prior to fast-feeding phases in both I. scapularis and A. maculatum suggesting a functional link with bloodmeal uptake. QC enzymatic activity was detected in saliva and extracts of tick salivary glands and midguts. Recombinant QC was shown to be catalytically active. Furthermore, knockdown of QC transcript by RNA interference resulted in lower enzymatic activity, and small, unviable egg masses in both studied tick species as well as lower engorged tick weights for I. scapularis. These results suggest that the post-translational modification of neurotransmitters and other bioactive peptides by QC is critical to oviposition and potentially other physiological processes. Moreover, these data suggest that tick-specific QC-modified neurotransmitters/hormones or other relevant parts of this system could potentially be used as novel physiological targets for tick control.

Characterization of Ixophilin, a thrombin inhibitor from the gut of Ixodes scapularis

Ixodes scapularis, the black-legged tick, vectors several human pathogens including Borrelia burgdorferi, the agent of Lyme disease in North America. Pathogen transmission to the vertebrate host occurs when infected ticks feed on the mammalian host to obtain a blood meal. Efforts to understand how the tick confronts host hemostatic mechanisms and imbibes a fluid blood meal have largely focused on the anticoagulation strategies of tick saliva. The blood meal that enters the tick gut remains in a fluid state for several days during the process of feeding, and the role of the tick gut in maintaining the blood-meal fluid is not understood. We now demonstrate that the tick gut produces a potent inhibitor of thrombin, a key enzyme in the mammalian coagulation cascade. Chromatographic fractionation of engorged tick gut proteins identified one predominant thrombin inhibitory activity associated with an approximately 18 kDa protein, henceforth referred to as Ixophilin. The ixophilin gene was preferentially transcribed in the guts of feeding nymphs. Expression began after 24 hours of feeding, coincident with the flow of host blood into the tick gut. Immunity against Ixophilin delayed tick feeding, and decreased feeding efficiency significantly. Surprisingly, immunity against Ixophilin resulted in increased Borrelia burgdorferi transmission to the host, possibly due to delayed feeding and increased transmission opportunity. These observations illuminate the potential drawbacks of targeting individual tick proteins in a functional suite. They also underscore the need to identify the “anticoagulome” of the tick gut, and to prioritize a critical subset of anticoagulants that could be targeted to efficiently thwart tick feeding, and block pathogen transmission to the vertebrate host.

Fourier transform infrared spectroscopy of DNA from Borrelia burgdorferi sensu lato and Ixodes ricinus ticks

In this work we present a method for detection of motile and immotile Borrelia burgdorferi genomic DNA, in relation with infectious and noninfectious spirochetes. An FT-IR study of DNA isolated from B. burgdorferi sensu lato strains and from positive and negative Ixodes ricinus ticks, respectively, is reported. Motile bacterial cells from the species B. burgdorferi sensu stricto, Borrelia garinii and Borrelia afzelii were of interest. Also, FT-IR absorbance spectra of DNA from immotile spirochetes of B. burgdorferi sensu stricto, in the absence and presence of different antibiotics (doxycycline, erythromycin, gentamicin, penicillin V or phenoxymethylpenicillin, tetracycline, respectively) were investigated. FT-IR spectra, providing a high molecular structural information, have been analyzed in the wavenumber range 400-1800 cm(-1). FT-IR signatures, spectroscopic band assignments and structural interpretations of these DNAs are reported. Spectral differences between FT-IR absorbances of DNAs from motile bacterial cells and immotile spirochetes, respectively, have been found. Particularly, alterations of the sugar-phosphate B-form chain in the case of DNA from Borrelia immotile cells, as compared with DNA from B. burgdorferi sensu lato motile cells have been observed. Based on this work, specific B. burgdorferi sensu lato and I. ricinus DNA-ligand interactions, respectively, might be further investigated using Fourier transform infrared spectroscopy.

Tryptogalinin is a tick Kunitz serine protease inhibitor with a unique intrinsic disorder

BACKGROUND

A salivary proteome-transcriptome project on the hard tick Ixodes scapularis revealed that Kunitz peptides are the most abundant salivary proteins. Ticks use Kunitz peptides (among other salivary proteins) to combat host defense mechanisms and to obtain a blood meal. Most of these Kunitz peptides, however, remain functionally uncharacterized, thus limiting our knowledge about their biochemical interactions.

RESULTS

We discovered an unusual cysteine motif in a Kunitz peptide. This peptide inhibits several serine proteases with high affinity and was named tryptogalinin due to its high affinity for β-tryptase. Compared with other functionally described peptides from the Acari subclass, we showed that tryptogalinin is phylogenetically related to a Kunitz peptide from Rhipicephalus appendiculatus, also reported to have a high affinity for β-tryptase. Using homology-based modeling (and other protein prediction programs) we were able to model and explain the multifaceted function of tryptogalinin. The N-terminus of the modeled tryptogalinin is detached from the rest of the peptide and exhibits intrinsic disorder allowing an increased flexibility for its high affinity with its inhibiting partners (i.e., serine proteases).

CONCLUSIONS

By incorporating experimental and computational methods our data not only describes the function of a Kunitz peptide from Ixodes scapularis, but also allows us to hypothesize about the molecular basis of this function at the atomic level.

Receptors for the neuropeptides, myoinhibitory peptide and SIFamide, in control of the salivary glands of the blacklegged tick Ixodes scapularis

Tick salivary glands are important organs that enable the hematophagous feeding of the tick. We previously described the innervation of the salivary gland acini types II and III by a pair of protocerebral salivary gland neurons that produce both myoinhibitory peptide (MIP) and SIFamide (Šimo et al., 2009b). In this study we identified authentic receptors expressed in the salivary glands for these neuropeptides. Homology-based searches for these receptors in the Ixodes scapularis genome sequence were followed by gene cloning and functional expression of the receptors. Both receptors were activated by low nanomolar concentrations of their respective ligands. The temporal expression patterns of the two ligands and their respective receptors suggest that the SIFamide signaling system pre-exists in unfed salivary glands, while the MIP system is activated upon initiation of feeding. Immunoreactivity for the SIFamide receptor in the salivary gland was detected in acini types II and III, surrounding the acinar valve and extending to the basal region of the acinar lumen. The location of the SIFamide receptor in the salivary glands suggests three potential target cell types and their probable functions: myoepithelial cell that may function in the contraction of the acini and/or the control of the valve; large, basally located dopaminergic granular cells for regulation of paracrine dopamine; and neck cells that may be involved in the control of the acinar duct and its valve.

Discovery of antagonists of tick dopamine receptors via chemical library screening and comparative pharmacological analyses

Ticks transmit a wide variety of disease causing pathogens to humans and animals. Considering the global health impact of tick-borne diseases, there is a pressing need to develop new methods for vector control. We are exploring arthropod dopamine receptors as novel targets for insecticide/acaricide development because of their integral roles in neurobiology. Herein, we developed a screening assay for dopamine receptor antagonists to further characterize the pharmacological properties of the two D₁-like dopamine receptors (Isdop1 and Isdop2) identified in the Lyme disease vector, Ixodes scapularis, and develop a screening assay for receptor antagonists. A cell-based, cyclic AMP luciferase reporter assay platform was implemented to screen the LOPAC(1280) small molecule library for Isdop2 receptor antagonists, representing the first reported chemical library screen for any tick G protein-coupled receptor. Screening resulted in the identification of 85 "hit" compounds with antagonist activity at the Isdop2 receptor. Eight of these chemistries were selected for confirmation assays using a direct measurement of cAMP, and the effects on both Isdop1 and Isdop2 were studied for comparison. Each of these eight compounds showed antagonistic activity at both Isdop1 and Isdop2, although differences were observed regarding their relative potencies. Furthermore, comparison of the pharmacological properties of the tick dopamine receptors with that of the AaDOP2 receptor from the yellow fever mosquito and the human dopamine D₁ receptor (hD₁) revealed species-specific pharmacological profiles of these receptors. Compounds influencing dopaminergic functioning, such as the dopamine receptor antagonists discovered here, may provide lead chemistries for discovery of novel acaricides useful for vector control

[Immunomodulating effect of an Ixodes persulcatus (Ixodidae) tick salivary gland extract on BALB/c mice lymphocytes in an in vitro system]

The immunomodulating effect of the components of an Ixodes persulcatus (Ixodidae) tick salivary gland extract (SGE) on BALB/c mice lymphocytes was evaluated. SGE of partially engorged ticks at a concentration of 50 microg/ml causes the maximum suppression ofT- and B-lymphocyte subpopulations. SGE of hungry ticks at the same concentration induces the suppression of only CD69+ T cells and TLR-2+ B cells, but produces no suppressive effect on CD69+ B lymphocytes, TLR-2+ T lymphocytes, and TLR-4+ T and B lymphocytes. SGE shows different effects on the synthesis of IFN-gamma and IL-4 by T helper cells. SGE of hungry ticks stimulated the increase of IFN-gamma and IL-4 synthesis by 4.7 and 2.6 times, respectively, as compared to the control. The findings may be of value in studying the pathogenesis of transmissible infections and in designing the vaccines based on tick gland components.

Expression of Ixodes scapularis antifreeze glycoprotein enhances cold tolerance in Drosophila melanogaster

Drosophila melanogaster experience cold shock injury and die when exposed to low non-freezing temperatures. In this study, we generated transgenic D. melanogaster that express putative Ixodes scapularis antifreeze glycoprotein (IAFGP) and show that the presence of IAFGP increases the ability of flies to survive in the cold. Male and female adult iafgp-expressing D. melanogaster exhibited higher survival rates compared with controls when placed at non-freezing temperatures. Increased hatching rates were evident in embryos expressing IAFGP when exposed to the cold. The TUNEL assay showed that flight muscles from iafgp-expressing female adult flies exhibited less apoptotic damage upon exposure to non-freezing temperatures in comparison to control flies. Collectively, these data suggest that expression of iafgp increases cold tolerance in flies by preventing apoptosis. This study defines a molecular basis for the role of an antifreeze protein in cryoprotection of flies.

The defensin gene family expansion in the tick Ixodes scapularis

Ixodid ticks transmit a variety of pathogens by blood feeding. Here, we report computational identification of two multigene families of defensin-like peptides (DLPs) in the Ixodes scapularis genome, one corresponding to scapularisin and the other named scasin. Members in the scapularisin family share high sequence similarity to some antibacterial ancient invertebrate-type defensins (AITDs) isolated from primitive insects, arachnids, bivalvia, and fungi whereas scasins represent a novel family of DLPs identified by their overall acidic molecular surface and low sequence similarity to any known defensins. Codon-substitution models support neutral evolution in scapularisins but strong positive selection signal was found throughout the molecules of scasins. The synthetic γ-core region of scapularisin-20 exhibits a wide-spectrum of antimicrobial activity at micromolar concentrations. The finding of extensive gene expansion of DLPs in a vector arachnida may be valuable in the understanding of its role in pathogen transmission.

[Interaction of the Siberian and Far Eastern subtypes of tick-borne encephalitis virus in mammals with mixed infection. I. Factors influencing the type of interaction]

Polytypic strains containing the fragments of genes of Siberian and Far Eastern tick-borne encephalitis (TBE) virus subtypes were isolated from the brain of fatal TBE patients, the blood of TBE patients, and Ixodes persulcatus ticks in the foci of concomitant circulation of the two subtypes. The interaction of the Siberian and Far Eastern TBE virus subtypes was studied in the neural phase of the infection of albino mice and Syrian hamsters in order to understand conditions for formation of these strains and their role in the etiology of acute TBE. Their viral progeny was genotyped by reverse transcription-polymerase chain reaction and fluorescence hybridization assay with genotype-specific probes. Mixed infection showed an effect of synergism, independent reproduction of the two subtypes in the brain and spleen, competitive exclusion of one subtype from the viral population. The type of the Interaction depended on the species of animals, the properties of partner strains, and the target organ.

Tertiary structure-related activity of tick defensin (persulcatusin) in the taiga tick, Ixodes persulcatus

Defensins are small cysteine-rich cationic proteins found in both vertebrates and invertebrates constituting the front line of host innate immunity. To examine the importance of the tertiary structure of tick defensin in its antimicrobial activity, we synthesized two types of the peptides with tertiary structure or primary one on basis of the information of the sequence in the defensin originated from the taiga tick, Ixodes persulcatus. Chemically synthesized peptides were used to investigate the activity spectrum against Staphylococcus aureus, Borrelia garinii and flora-associated bacteria. Both synthetic peptides showed antimicrobial activity against S. aureus in short-time killing within 1 h, but they do not show the activity against B. garinii, Stenotrophomonas maltophila and Bacillus spp., which were frequently isolated from the midgut of I. persulcatus. The teriary structure brought more potent activity to S. aureus than primary one in short-time killing. We also examined its antimicrobial activity by evaluation of growth inhibition in the presence of the synthetic peptides. Minimum inhibitory concentration (MIC) was ranged from 1.2 to 5.0 μg/ml in tertiary peptide and from 10 to 40 μg/ml in primary peptide, when 10 strains of S. aureus were used. From the curve of cumulative inhibition rates, MIC50 (MIC which half of the strains showed) to S. aureus is about 1.2 μg/ml in the peptide with tertiary structure and about 10 μg/ml in the linear one. Corynebacterium renale is 10 times or more sensitive to tertiary peptide than primary one. In conclusion, the presence of 3 disulfide bridges, which stabilize the molecule and maintain the tertiary structure, is considered to have an effect on their antimicrobial activities against Gram-positive bacteria such as S. aureus.

[Estimation of the biological age in taiga tick females (Ixodes persulcatus:Ixodidae) by the fat reserves in organism]

The method of estimation of the biological age in non-feeding tick females by the level of adipose inclusions in the cells of the midgut and fat body is developed. In order to estimate the fat reserves in non-feeding females, alive ticks were dissected and fragments of their internal were vitally stained with the pregnant solution of sudan III in 70 % ethanol. Three age-specific groups were established: I, young females whose intestines and fat body were filled with fat inclusions; II, mature females whose fat reserves were partially expended; III, old females having isolated fat inclusions in their midgut and fat body.

The immunomodulatory action of sialostatin L on dendritic cells reveals its potential to interfere with autoimmunity

Sialostatin L (SialoL) is a secreted cysteine protease inhibitor identified in the salivary glands of the Lyme disease vector Ixodes scapularis. In this study, we reveal the mechanisms of SialoL immunomodulatory actions on the vertebrate host. LPS-induced maturation of dendritic cells from C57BL/6 mice was significantly reduced in the presence of SialoL. Although OVA degradation was not affected by the presence of SialoL in dendritic cell cultures, cathepsin S activity was partially inhibited, leading to an accumulation of a 10-kDa invariant chain intermediate in these cells. As a consequence, in vitro Ag-specific CD4(+) T cell proliferation was inhibited in a time-dependent manner by SialoL, and further studies engaging cathepsin S(-/-) or cathepsin L(-/-) dendritic cells confirmed that the immunomodulatory actions of SialoL are mediated by inhibition of cathepsin S. Moreover, mice treated with SialoL displayed decreased early T cell expansion and recall response upon antigenic stimulation. Finally, SialoL administration during the immunization phase of experimental autoimmune encephalomyelitis in mice significantly prevented disease symptoms, which was associated with impaired IFN-gamma and IL-17 production and specific T cell proliferation. These results illuminate the dual mechanism by which a human disease vector protein modulates vertebrate host immunity and reveals its potential in prevention of an autoimmune disease.

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.

Ixodes ticks belonging to the Ixodes ricinus complex encode a family of anticomplement proteins

The alternative pathway of complement is an important innate defence against pathogens including ticks. This component of the immune system has selected for pathogens that have evolved countermeasures. Recently, a salivary protein able to inhibit the alternative pathway was cloned from the American tick Ixodes scapularis (Valenzuela et al., 2000; J. Biol. Chem. 275, 18717-18723). Here, we isolated two different sequences, similar to Isac, from the transcriptome of I. ricinus salivary glands. Expression of these sequences revealed that they both encode secreted proteins able to inhibit the complement alternative pathway. These proteins, called I. ricinus anticomplement (IRAC) protein I and II, are coexpressed constitutively in I. ricinus salivary glands and are upregulated during blood feeding. Also, we demonstrated that they are the products of different genes and not of alleles of the same locus. Finally, phylogenetic analyses demonstrate that ticks belonging to the Ixodes ricinus complex encode a family of relatively small anticomplement molecules undergoing diversification by positive Darwinian selection.

[Biochemical characteristics of ticks of the families Argasidae and Ixodidae]

Polyacrylamide gel electrophoresis was used to study homogenate supernatants from the bloodsucking ticks (Argasidae and Ixodidae) belonging to 8 different genera and species. Differences were found in the electrophoretic mobility of protein fractions in adult ticks of these two different families and between several genera of Ixodes ticks (such as Haemaphysalis, Hyalomma, Dermacentor, Rhipicephalus and Ixodes). Argasidae ticks were found to have generic and even species-specific differences at the nymphal stage of development. A. lahorensis nymph-3 contained 5 protein fractions; O. papillipes had 2 fractions, and O. moubata had 3 fractions. Electrophoretic protein separation showed the equal number of protein fractions within one genus of ticks. At the larval stage, the tick homogenates were always found to have one protein fraction. The hemolymph of O. papillipes and O. moubata ticks displayed differences between the imago and nymph-3. A new biochemical marker was proposed to establish a species affinity.

Ixodes ricinus: the potential of two-dimensional gel electrophoresis as a tool for studying host-vector-pathogen interactions

Ixodes ricinus is a three-host tick, with three active instars. For moulting to occur the tick has to find a host where it can take a blood meal. Throughout feeding I. ricinus can be infected or infect the host with different pathogens, e.g., Tick-Borne Encephalitis virus or Borrelia burgdorferi. The host-vector-pathogen interaction is very complex, making a detailed study difficult. Here we analyse the potential of two-dimensional gel electrophoresis (2DE) to study the host-vector-pathogen interaction. We examined 20 nymphs, which as larvae parasitised either mouse or hen. After moulting, they were kept alive for up to 30 weeks, to analyse whether tick ageing influenced host determination, and for comparison of the 2D-gels. Even though the number of proteins in the gel decreased during ageing, some proteins of the host determination persisted for all 30 weeks. We also discovered persisting proteins in relation to nymphs. These findings showed that 2DE is suitable as a tool for studying host-vector-pathogen interactions.

Structural identification of an anthrasteroid hydrocarbon from the sheep tick Ixodes ricinus

A new anthrasteroid hydrocarbon was isolated from cuticular integument of engorged female Ixodes ricinus, and its structure was determined by interpretation of spectroscopic and nuclear magnetic resonance data as 14alpha(H)-1(10-->6)-abeo-cholesta-3,5,7,9(10)-tetraene (1).

Antiinflammatory and immunosuppressive activity of sialostatin L, a salivary cystatin from the tick Ixodes scapularis

Here we report the ability of the tick Ixodes scapularis, the main vector of Lyme disease in the United States, to actively and specifically affect the host proteolytic activity in the sites of infestation through the release of a cystatin constituent of its saliva. The cystatin presence in the saliva was verified both biochemically and immunologically. We named the protein sialostatin L because of its inhibitory action against cathepsin L. We also show that the proteases it targets, although limited in number, have a prominent role in the proteolytic cascades that take place in the extracellular and intracellular environment. As a result, sialostatin L displays an antiinflammatory role and inhibits proliferation of cytotoxic T lymphocytes. Beyond unraveling another component accounting for the properties of tick saliva, contributing to feeding success and pathogen transmission, we describe a novel tool for studying the role of papain-like proteases in diverse biologic phenomena and a protein with numerous potential pharmaceutical applications.

Effect of salivary gland extract from Ixodes ricinus ticks on the proliferation of Borrelia burgdorferi sensu stricto in vivo

Saliva-activated transmission (SAT) of Borrelia burgdorferi sensu stricto was demonstrated using real-time PCR and salivary gland extract (SGE) from partially fed Ixodes ricinus ticks. C3H/HeN mice were injected intradermally with 1.5 x 10(3) spirochetes mixed with 40 microg of SGE per mouse. The control group was inoculated with the same dose of spirochetes without SGE. The accelerating effect of SGE on spirochete proliferation was demonstrated on day 1 post infection, when a 4.2-fold increase in spirochetes was found in the skin and a 10-fold increase in the blood, compared with control mice. The data represent the first direct evidence of a SAT effect of I. ricinus SGE on infection with the Lyme disease agent B. burgdorferi.

Anti-hemostatic effects of a serpin from the saliva of the tick Ixodes ricinus

Serpins (serine protease inhibitors) are a large family of structurally related proteins found in a wide variety of organisms, including hematophagous arthropods. Protein analyses revealed that Iris, previously described as an immunomodulator secreted in the tick saliva, is related to the leukocyte elastase inhibitor and possesses serpin motifs, including the reactive center loop (RCL), which is involved in the interaction between serpins and serine proteases. Only serine proteases were inhibited by purified recombinant Iris (rIris), whereas mutants L339A and A332P were found devoid of any protease inhibitory activity. The highest Ka was observed with human leukocyte-elastase, suggesting that elastase-like proteases are the natural targets of Iris. In addition, mutation M340R completely changed both Iris substrate specificity and affinity. This likely identified Met-340 as amino acid P1 in the RCL. The effects of rIris and its mutants were also tested on primary hemostasis, blood clotting, and fibrinolysis. rIris increased platelet adhesion, the contact phase-activated pathway of coagulation, and fibrinolysis times in a dose-dependent manner, whereas rIris mutant L339A affected only platelet adhesion. Taken together, these results indicate that Iris disrupts coagulation and fibrinolysis via the anti-proteolytic RCL domain. One or more other domains could be responsible for primary hemostasis inhibition. To our knowledge, this is the first ectoparasite serpin that interferes with both hemostasis and the immune response.

Optimization of the solid-phase microextraction method in the determination ofIxodes ricinus (L.) volatiles

For the first time, headspace solid-phase microextraction coupled with GC-MS analysis was used to study volatile compounds emitted by the tick Ixodes ricinus (L.). Variables such as the type of SPME fibre, equilibration time and extraction time have been evaluated with the mixture of four selected standards, a so-called artificial tick (acetophenone, racemic 4-heptanolide, methyl 2-methoxybenzoate and methyl 3-chloro-4-methoxybenzoate). Optimized conditions were obtained by the use of polydimethylsiloxan 100 microm fibre at 30 min equilibration and 15 min extraction time. The method proved to have a good linearity (r2 >0.98) at a concentration range from 0.5 ng (1 ng for methyl 3-chloro-4-methoxybenzoate) to 25 ng. LODs for a compound ranged between 0.19 and 1 ng, RSD (%) ranged from 13.76 to 25.08. The determination of 1.99 ng of methyl 3-chloro-4-methoxybenzoate emitted by five engorged females proved the usefulness of the developed method to identify and quantify the volatile compounds emitted by I. ricinus ticks.

Molecular cloning and comparative analysis of fibrinogen-related proteins from the soft tick Ornithodoros moubata and the hard tick Ixodes ricinus

Among disease-vectors, the evolution of the tick innate immune system is still lagging when compared to insects. Such an investigation, which was initiated, by first cloning and sequencing lectins associated in the innate immunity of invertebrates and having fibrinogen related domains, helped in the sequencing of cDNA encoding for OMFREP from the soft tick, Ornithodoros moubata. Also obtained were Ixoderin A and Ixoderin B cDNA sequences from the hard tick Ixodes ricinus. Tissue-specific expression of OMFREP showed that it was present primarily in the hemocytes and salivary glands. Ixoderin A besides sharing a similar expression profile was also expressed in the midgut. Both showed significantly high homology to the lectin Dorin M, from O. moubata. Further, phylogenetic comparisons between these molecules of the soft and hard ticks showed their relatedness to Tachylectins 5A and 5B, involved in the innate immunity of Tachypleus tridentatus and ficolins from both vertebrates and invertebrates. Ixoderin B showing tissue-specific expression only in the salivary glands and the sequence displaying certain motif differences in homology point towards a possible function different from the other two molecules. This is the first report of lectin-like sequences, with a fibrinogen-domain, from the hard tick I. ricinus and a preliminary phylogenetic study of these tick sequences with related fibrinogen-domain containing sequences highlights a possible role for them in the innate immunity of the ticks.

Boophilus microplus tick larvae, a rich source of Kunitz type serine proteinase inhibitors

Serine proteinase inhibitors from Boophilus microplus tick larvae (BmTIs) were purified by affinity chromatography on a trypsin-Sepharose column. BmTIs presented molecular weight between M(r) 6200 and 18,400 and inhibitory activity for trypsin, HuPK (human plasma kallikrein) and neutrophil elastase. Using ion exchange chromatography, BmTIs were separated in several protein pools named BmTI-A to BmTI-F and BmTI-1 to BmTI-7. All BmTI forms presented inhibitory activity for trypsin with apparent dissociation constants (K(i)) in the nM range. In this work, we describe the purification of BmTI-D, BmTI-2, and BmTI-3. These three inhibitors affected neutrophil elastase and HuPK with K(i) also in nM range. BmTI-D proved to be the best HuPK inhibitor, while BmTI-3 was more efficient for neutrophil elastase with dissociation constants (K(i)) of 12 and 0.5 nM, respectively. BmTI-D, BmTI-2, and BmTI-3 N-terminal amino acid sequences allowed us to include them into the BPTI-Kunitz type serine proteinase inhibitor family. BmTIs purified on trypsin-Sepharose were also used in a bovine immunization assay, resulting in antibody (anti-BmTIs) production.

Cardiovascular effects of the toxin(s) of the Australian paralysis tick, Ixodes holocyclus, in the rat

An extract of toxin(s) from the Australian paralysis tick, Ixodes holocyclus, produced positive inotropic responses in rat left ventricular papillary muscles and positive contractile responses in rat thoracic aortic rings. There was no measurable chronotropic response in rat right atria, but positive inotropic concentrations in papillary muscles produced arrhythmias in right atria. Positive inotropic responses were attenuated by verapamil, but unaffected by metoprolol, cimetidine, pyrilamine, tetrodotoxin and pinacidil. Microelectrode studies on isolated left ventricular papillary muscles demonstrated that the extract prolonged action potential duration at 20, 50 and 90% of repolarisation and delayed ventricular papillary muscle relaxation. Cardiovascular tissues isolated from rats with experimentally induced tick paralysis showed no myocardial damage as identified by histological and ultrastructural examination. The basal rate and force of contraction of isolated cardiac tissues were lower from tick-paralysed than normal rats. Concentration-response curves to dobutamine and calcium chloride were similar between tissues from tick-paralysed and normal rats. Thus, the Australian paralysis tick, I. holocyclus, produces one or more toxins with direct cardiovascular effects which mimic the effects produced by direct blockade of cardiac and vascular K+ channels.

Cloning and sequencing of putative calreticulin complementary DNAs from four hard tick species

Calreticulin (CRT) is a calcium-binding protein and has many functions in eukaryotic cells. CRT is possibly involved in parasite host immune system evasion. To better understand the molecular basis of CRT in ticks, we cloned and sequenced 4 full-length complementary DNAs (cDNAs) from the hard tick species, Dermacentor variabilis, Haemaphysalis longicornis, Ixodes scapularis, and Rhipicephalus sanguineus, using the technique of rapid amplification of cDNA ends. The deduced amino acid sequences share high identities (between 77 and 98%) with 3 known tick CRT sequences. The major characteristics of known CRTs are observed in all 4 of our deduced tick CRTs. These include 3 major domains, a signal peptide sequence at the beginning of the coding region, 2 triplets of conserved regions, cysteine sites providing disulfide bridges for N-terminal folding, and a nuclear localization signal. Remarkably, the replacement of the endoplasmic reticulum retention signal KDEL by HEEL, which is believed to be associated with secretion of CRT into the host during feeding and was previously recorded only in 2 ticks and a hookworm, is also present in all 4 of our tick putative CRTs. In addition, the CRT gene is potentially useful for tick phylogenetic reconstruction.

Ixodes ricinus tick salivary gland extract inhibits IL-10 secretion and CD69 expression by mitogen-stimulated murine splenocytes and induces hyporesponsiveness in B lymphocytes

Tick saliva contains immunosuppressive factors allowing this blood-feeding ectoparasite to remain on hosts and enhancing pathogen transmission. In this study, we examined the modulation of mitogen-induced activation of naive murine splenocytes by the saliva and salivary gland extract (SGE) of I. ricinus ticks. We found that saliva-specific factors reduced IL-10 production by both concanavalin A (ConA) and lipopolysaccharide (LPS) stimulated splenocytes. The LPS-induced IL-10 production is 10 times more sensitive to SGE than the ConA-induced IL-10 production. Flow cytometric analysis determined that SGE particularly inhibited B (B220+) cell IL-10 production in mitogen-stimulated splenocyte preparations. Moreover, SGE reduced the early activation marker CD69 expression on ConA-activated T cells and also on B cells in presence of ConA or LPS. Annexin V and Via-probe staining demonstrated that SGE did not increase cell death in activated splenocytes and slightly decreased apoptosis in B lymphocytes. By employing assays with isolated B cells, we further showed that SGE had a direct effect on B cells and inhibited LPS-induced B cell proliferation. Taken together, our results indicate that salivary immunomodulators induce hyporesponsiveness to mitogen in both T and B cells, and that a direct B-cell inhibitory activity is present in tick saliva.

Salivary gland extract from Ixodes ricinus tick modulates the host immune response towards the Th2 cytokine profile

In our previous work, the salivary gland extract (SGE) from Ixodes ricinus ticks impaired T-lymphocyte proliferation and clearly modulated the immune response towards the Th2 pattern in human peripheral blood mononuclear cell culture. In the present work, the results obtained on mouse splenocytes are compared with those on human leukocytes. ELISA (protein level) and RNAse protection assay (mRNA level) showed that SGE enhanced interleukin (IL)-1alpha, IL-1beta, IL-1Ra, IL-6, and IL-12p40 cytokines, whereas production of IL-2, IL-5, IL-10, and IL-13 was decreased. The minute levels of IL-9, IL-15 and IL-12p70 were not changed after the addition of tick saliva. IL-4 was upregulated, whereas the production of gamma interferon and migratory inhibition factor was downregulated after the addition of SGE. Tick saliva decreased concanavalin A-stimulated spleen cell proliferation and the percentage of activated T-cells. We conclude that the Th2 polarization did not involve all of the cytokines tested. However, the Th2 subset-augmenting effect of tick saliva was confirmed.

An empirical quantitative framework for the seasonal population dynamics of the tick Ixodes ricinus

The wide geographic and climatic range of the tick Ixodes ricinus, and the consequent marked variation in its seasonal population dynamics, have a direct impact on the transmission dynamics of the many pathogens vectored by this tick species. We use long-term observations on the seasonal abundance and fat contents (a marker of physiological ageing) of ticks, and contemporaneous microclimate at three field sites in the UK, to establish a simple quantitative framework for the phenology (i.e. seasonal cycle of development) of I. ricinus as a foundation for a generic population model. An hour-degree tick inter-stadial development model, driven by soil temperature and including diapause, predicts the recruitment (i.e. emergence from the previous stage) of a single cohort of each stage of ticks each year in the autumn. The timing of predicted emergence coincides exactly with the new appearance of high-fat nymphs and adults in the autumn. Thereafter, fat contents declined steadily until unfed ticks with very low energy reserves disappeared from the questing population within about 1 year from their recruitment. Very few newly emerged ticks were counted on the vegetation in the autumn, but they appeared in increasing numbers through the following spring. Larger ticks became active and subsequently left the questing population before smaller ones. Questing tick population dynamics are determined by seasonal patterns of tick behaviour, host-contact rates and mortality rates, superimposed on a basal phenology that is much less complex than has hitherto been portrayed.

Ixolaris, a novel recombinant tissue factor pathway inhibitor (TFPI) from the salivary gland of the tick, Ixodes scapularis: identification of factor X and factor Xa as scaffolds for the inhibition of factor VIIa/tissue factor complex

Saliva of the hard tick and Lyme disease vector, Ixodes scapularis, has a repertoire of compounds that counteract host defenses. Following sequencing of an I scapularis salivary gland complementary DNA (cDNA) library, a clone with sequence homology to tissue factor pathway inhibitor (TFPI) was identified. This cDNA codes for a mature protein, herein called Ixolaris, with 140 amino acids containing 10 cysteines and 2 Kunitz-like domains. Recombinant Ixolaris was expressed in insect cells and shown to inhibit factor VIIa (FVIIa)/tissue factor (TF)-induced factor X (FX) activation with an inhibitory concentration of 50% (IC(50)) in the picomolar range. In nondenaturing gel, Ixolaris interacted stoichiometrically with FX and FXa but not FVIIa. Ixolaris behaves as a fast-and-tight ligand of the exosites of FXa and gamma-carboxyglutamic acid domainless FXa (des-Gla-FXa), increasing its amidolytic activity. At high concentration, Ixolaris attenuates the amidolytic activity of FVIIa/TF; however, in the presence of DEGR-FX or DEGR-FXa (but not des-Gla-DEGR-FXa), Ixolaris becomes a tight inhibitor of FVIIa/TF as assessed by recombinant factor IX (BeneFIX) activation assays. This indicates that FX and FXa are scaffolds for Ixolaris in the inhibition of FVIIa/TF and implies that the Gla domain is necessary for FVIIa/TF/Ixolaris/FX(a) complex formation. Additionally, we show that Ixolaris blocks FXa generation by endothelial cells expressing TF. Ixolaris may be a useful tool to study the structural features of FVIIa, FX, and FXa, and an alternative anticoagulant in cardiovascular diseases.

Comparison of the protein profiles of salivary gland extracts derived from three species of unfed and partially fed ixodid ticks analysed by SDS-PAGE

Salivary gland extracts (SGE) from unfed and 5 days fed adult female Ixodes ricinus (Linnaeus, 1758); Haemaphysalis inermis (Birula, 1895) and Dermacentor reticulatus (Fabricius, 1794) ticks were prepared. The protein content after feeding increased by 10.6, 8.7 and 6.8 times, respectively. Extracts were equilibrated to the same protein content and submitted to SDS-polyacrylamide gel electrophoresis followed by computer analysis of the scanned gels. Relative differences in protein profiles of extracts obtained from unfed and partially fed ticks were found in all species and some of them were similar in all three species used in the study. Results demonstrate that the increase of the protein content in salivary glands during the feeding does not occur proportionally. Some proteins are synthesised preferentially (67.1 kDa, 13.5 kDa) but other bands (in range of 15-16 kDa) present in the SGE derived from unfed ticks are less discernible in that of fed ticks.

SALP16, a gene induced in Ixodes scapularis salivary glands during tick feeding

Guinea pigs infested with Ixodes scapularis acquire antibody-mediated resistance to tick bites, a phenomenon known as tick-immunity. An I. scapularis salivary gland cDNA expression library was therefore probed with sera from tick-immune guinea pigs to identify antigens that elicit humoral responses in the host. Sera from sensitized guinea pigs strongly recognized 3 of 4,500 library clones in an initial screening. The open reading frames of all 3 clones encoded a putative 16.4-kD acidic protein, designated Salp16, with an N-terminal signal sequence and signal peptidase cleavage sites specific for secretory proteins. The salp16 mRNA and Salp16 protein were detected in the salivary glands of engorged, but not unfed, nymphal and adult ticks, and Salp16 was also found in the saliva of engorged ticks. Immunization with recombinant Salp16 induced high antibody titers in guinea pigs, but did not elicit tick-immunity. Salp16 is the first feeding inducible gene that has been cloned from L. scapularis. Molecular characterization of I. scapularis salivary antigens that are induced upon tick feeding should help to facilitate our understanding of tick-host interactions.

Comparison of surface proteins of Anaplasma marginale grown in tick cell culture, tick salivary glands, and cattle

Anaplasma marginale, a tick-borne rickettsial pathogen of cattle, infects bovine erythrocytes, resulting in mild to severe hemolytic disease that causes economic losses in domestic livestock worldwide. Recently, the Virginia isolate of A. marginale was propagated in a continuous tick cell line, IDE8, derived from embryonic Ixodes scapularis. Development of A. marginale in cell culture was morphologically similar to that described previously in ticks. In order to evaluate the potential of the cell culture-derived organisms for use in future research or as an antigen for serologic tests and vaccines, the extent of structural conservation of the major surface proteins (MSPs) between the cell culture-derived A. marginale and the bovine erythrocytic stage, currently the source of A. marginale antigen, was determined. Structural conservation on the tick salivary-gland stage was also examined. Monoclonal and monospecific antisera against MSPs 1 through 5, initially characterized against erythrocyte stages, also reacted with A. marginale from cell culture and tick salivary glands. MSP1a among geographic A. marginale isolates is variable in size because of different numbers of a tandemly repeated 28- or 29-amino-acid peptide. The cell culture-derived A. marginale maintained the same-size MSP1a as that found on the Virginia isolate of A. marginale in bovine erythrocytes and tick salivary glands. Although differences were observed in the polymorphic MSP2 antigen between culture and salivary-gland stages, MSP2 did not appear to vary, by two-dimensional gel electrophoresis, during continuous passage in culture. These data show that MSPs of erythrocyte-stage A. marginale are present on culture stages and may be structurally conserved during continuous culture. The presence of all current candidate diagnostic and vaccine antigens suggests that in vitro cultures are a valuable source of rickettsiae for basic research and for the development of improved diagnostic reagents and vaccines against anaplasmosis.

Ixodes ricinus strains in Europe

An analysis of cuticular hydrocarbons (CH) of unfed adult Ixodes ricinus ticks collected throughout Europe showed that there are 10 distinct I. ricinus groups. Studies on the seasonal and annual consistency of CH composition and possible effects of host and environmental factors suggested that CHs may be used as a genuine genetic marker for I. ricinus. Preliminary studies compared the vector competence of ticks from three of the most separated I. ricinus groups and the results suggested that there may be significant differences in tick susceptibility to Borrelia afzelii.

Ecdysteroid regulation of salivary gland degeneration in the ixodid tick, Amblyomma hebraeum: a reconciliation of in vivo and in vitro observations

Salivary gland degeneration in the female tick Amblyomma hebraeum Koch is triggered by an ecdysteroid (ES) hormone. Under both in vivo and in vitro conditions, degeneration requires 4 days for completion. In partially fed females that have fed beyond a "critical weight," the commitment period for salivary gland degeneration occurs between 24 and 48 h after removal from the host. Although tissue degeneration begins within 24 h postengorgement, ES titer as measured by radioimmunoassay (RIA) does not rise to threshold levels until 48 h postengorgement. To explain this anomaly we examined two hypotheses: (1) there is an early hormonal signal (e.g., 3-dehydroecdysone; 3DE) that is an ES not detectable by the antibody used in our RIA; and (2) the low hemolymph titer during the first 2 days postengorgement is not an accurate reflection of the ES concentration within the tissue itself. 3-Oxoecdysteroid 3 beta-reductase (ketoreductase) was present in salivary glands, but neither ketoreductase nor 3DE was detected in hemolymph. The ES concentration of salivary gland homogenates was similar to that of hemolymph, while that of saliva was undetectable. Together, these results support our second hypothesis that the metabolically active tissue of the salivary gland experiences a suprathreshold concentration of hormone even though the concentration in hemolymph is below threshold levels.

Purification and partial characterization of vitellin from the black-legged tick, Ixodes scapularis

Vitellin from the black-legged tick, Ixodes scapularis, was purified from eggs using gel filtration and ion exchange chromatography. The purified protein had a native molecular mass of 480 kDa. Under reducing conditions (sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SDS-PAGE), vitellin was composed of seven polypeptides each at 154, 135, 87, 78, 67, 64 and 35 kDa. The isoelectric point was pH 6.9 and absorption maxima for the yolk protein were 280 and 400 nm. As in other ticks, vitellin from I. scapularis is also a hemoglycolipoprotein. Carbohydrates detected in vitellin were predominantly mannose with a small amount of N-acetylglucosamine. Lipids detected by thin layer chromatography (TLC) were triglycerides, free fatty acids, and cholesterol. Phospholipids associated with vitellin were phosphatidylethanolamine and phosphatidylcholine. Polyclonal serum produced in rabbits recognized vitellin from the eggs and ovaries, and vitellogenin from the hemolymph and fat body in reproductive females. This is the first report on the characterization of yolk proteins from a prostriate tick.

Plasminogen is required for efficient dissemination of B. burgdorferi in ticks and for enhancement of spirochetemia in mice

The role of the host plasminogen activation system in transmission of and invasion by Borrelia burgdorferi, the tick-borne spirochetal agent of Lyme disease, was investigated using plasminogen (Plg)-knockout mice. PLG was not detected in spirochetes from unfed ticks, but binding occurred as ticks fed on the host's blood. Plasminogen activators were derived from the host blood meal. PLG was required for efficient dissemination of B. burgdorferi within the tick and for enhancement of spirochetemia in mice but was not critical for transmission and infection. These results provide evidence for a bacterium using a vertebrate protease to disseminate in an invertebrate vector and underscores the interplay among vector, pathogen, and host in promoting the life cycle and disease.

Tick-borne encephalitis virus (TBEV)-specific RT-PCR for characterization of natural foci of TBE and for other applications

An effective detection system for TBEV-RNA sequences using a RT-PCR technique has been developed. In our system, specific oligonucleotide primers corresponding to the 5'-terminal noncoding region were successfully used to identify TBEV sequences in ticks. To prove the specificity of the PCR products, Southern blot hybridization with an internal digoxigenin-labelled probe was carried out. In this paper, we present some potential applications of this technique. The primers were used to identify 21 TBEV strains isolated in different years, in different geographic regions and from different sources. 22313 Ixodes ricinus ticks from north-east Germany were analyzed for TBEV-specific sequences in order to characterize the viral activity in natural foci of TBE. In the new Federal Länder, only 6 samples gave positive PCR-results, showing that the natural foci of TBE had not been extinguished but remained in a state of endemic latency. We also used the RT-PCR to develop an animal model to investigate the temporal pattern of viraemia in the Mongolian gerbil (Meriones unguiculatus) through xenodiagnosis (sequential tick feeding on an infected host and subsequent RT-PCR testing of the resultant engorged ticks).

Ultrastructural localization of a sialic acid-specific hemolymph lectin in the hemocytes and other tissues of the hard tick Ixodes ricinus (Acari; Chelicerata)

Lectins have been suggested to function as pattern-recognition molecules in invertebrate immune mechanisms. A lectin from the hemolymph of the tick Ixodes ricinus with main specificity for sialic acid was characterized and antibodies directed against this lectin were prepared. In this study, these antibodies were used to localize the lectin in the tissues of I. ricinus. Immunoreactivity with poly- and monoclonal antibodies was detected in the granules of both types of granular hemocytes, at the membrane of hemocytes, and at the basal laminae surrounding the hemocoel. Furthermore, cells attached to the midgut, invaginations of Géné's organ, and granular inclusions of nephrocytes were labeled. The immunoreactivity detected in hemocytes and the hemocoel lining supports the idea that the hemolymph lectin may function as a recognition molecule in the immune system of I. ricinus. Another function could be protection of eggs that are coated with secretions by Géné's organ. The lectin activity could also be involved in transmission of Borrelia burgdorferi, the causative agent of Lyme borreliosis, and the tick-borne encephalitis virus.