Saliva of Rhipicephalus sanguineus tick impairs T cell proliferation and IFN-gamma-induced macrophage microbicidal activity

mRNA vaccination induces tick resistance and prevents transmission of the Lyme disease agent

Ixodes scapularis ticks transmit many pathogens that cause human disease, including Borrelia burgdorferi. Acquired resistance to I. scapularis due to repeated tick exposure has the potential to prevent tick-borne infectious diseases, and salivary proteins have been postulated to contribute to this process. We examined the ability of lipid nanoparticle–containing nucleoside-modified mRNAs encoding 19 I. scapularis salivary proteins (19ISP) to enhance the recognition of a tick bite and diminish I. scapularis engorgement on a host and thereby prevent B. burgdorferi infection. Guinea pigs were immunized with a 19ISP mRNA vaccine and subsequently challenged with I. scapularis. Animals administered 19ISP developed erythema at the bite site shortly after ticks began to attach, and these ticks fed poorly, marked by early detachment and decreased engorgement weights. 19ISP immunization also impeded B. burgdorferi transmission in the guinea pigs. The effective induction of local redness early after I. scapularis attachment and the inability of the ticks to take a normal blood meal suggest that 19ISP may be used either alone or in conjunction with traditional pathogen-based vaccines for the prevention of Lyme disease, and potentially other tick-borne infections.

Anti-tick and pathogen transmission blocking vaccines

Ticks and tick-borne diseases are a challenge for medical and veterinary public health and often controlled through the use of repellents and acaricides. Research on vaccination strategies to protect humans, companion animals, and livestock from ticks and tick-transmitted pathogens has accelerated through the use of proteomic and transcriptomic analyses. Comparative analyses of unfed versus engorged and uninfected versus infected ticks have provided valuable insights into candidates for anti-tick and pathogen transmission blocking vaccines. An intricate interplay between tick saliva and the host's immune system has revealed potential antigens to be used in vaccination strategies. Immunization of hosts with targeted anti-tick vaccines would ideally lead to a reduction in tick numbers and prevent transmission of tick-borne pathogens. Comprehensive control of tick-borne diseases would come from successful anti-tick vaccination, vaccination preventing transmission of tick-borne diseases or a combination. Due to the close interaction with wildlife and ticks, with wildlife reservoirs enabling propagation of pathogens between ticks, the vaccination of these reservoirs is an attractive target to reduce human contact with ticks and tick-borne diseases through a one-health approach. Wildlife vaccination presents formulation and regulatory challenges which should be considered early in the development of reservoir-targeted vaccines.

Rhipicephalus sanguineus salivary gland extract as a source of immunomodulatory molecules

Rhipicephalus sanguineus sensu lato (s.l.), popularly known as 'brown dog tick', is the primary vector of pathogens affecting dogs worldwide. To enter the host's organism, these pathogens utilise the anticoagulant, antiplatelet, anti-inflammatory and immunomodulatory actions of compounds present in the tick's saliva; such compounds are released by the ectoparasite in order to attach and feed on dogs. Nitric oxide (NO) is one of the regulatory factors in inflammation, apoptosis and immunomodulation. Here, we evaluated the in vitro activity of salivary gland extract of female dog ticks on the macrophage-derived J774 cell line, with and without lipopolysaccharide (LPS) stimulation. Cultures were evaluated for possible morphological alterations caused by exposure to the extract. There was no apparent in vitro cytotoxicity of the extract. Also, the NO secretory response in the non-LPS-stimulated cells was not inhibited. On the other hand, the extract presented modulatory action in the cultures of LPS-stimulated cells at a concentration of 0.1 μg/mL, possibly through macrophage activation, and induced a significant decrease in NO secretion. These results confirm the modulatory potential of bioactive molecules in the salivary glands of R. sanguineus ticks.

Rhipicephalus microplus serpins interfere with host immune responses by specifically modulating mast cells and lymphocytes

Rhipicephalus microplus ticks feed on a bovine host for three weeks. At the attachment site, inflammatory and immune responses are triggered resulting in the recruitment of cells and production of a set of immunological mediators. To oppose the host's immune responses, ticks inoculate bioactive salivary molecules capable of interfering with these defense mechanisms. Serpins are among the most frequent molecules present in tick saliva and have been shown to negatively affect the host's anti-tick immunity. R. microplus has at least eighteen full-length serpins (RmS) and eleven are transcribed during blood feeding. Among them, RmS-3, RmS-6, and RmS-17 are present in the saliva of engorged females. Here, the effect of these serpins on the immune responses was evaluated in cells involved in innate/inflammatory (mast cells and macrophages) and adaptive (T cells) immunity. RmS-3 modulated mast cells due to its inhibitory activity on peritoneal rat chymase and on vascular permeability in acute inflammation. In addition, both RmS-6 and RmS-17 inhibited vascular permeability. Of the three serpins studied, neither affected activation nor inflammatory cytokine production by murine macrophages. On the other hand, RmS-3 and RmS-17 presented an inhibitory effect on the metabolic activity of lymphocytes, with the latter being the most potent, while RmS-6 had no effect on it. This activity was associated with a decrease in lymphocyte proliferation, but not with induction of cell death. The present study highlights the powerful modulatory role of tick salivary serpins in the host's immune system and inspire the discovery of targets for the treatment of inflammatory/immune disorders.

Amblyomma americanum ticks utilizes countervailing pro and anti-inflammatory proteins to evade host defense

Feeding and transmission of tick-borne disease (TBD) agents by ticks are facilitated by tick saliva proteins (TSP). Thus, defining functional roles of TSPs in tick evasion is expected to reveal potential targets in tick-antigen based vaccines to prevent TBD infections. This study describes two types of Amblyomma americanum TSPs: those that are similar to LPS activate macrophage (MΦ) to express pro-inflammation (PI) markers and another set that suppresses PI marker expression by activated MΦ. We show that similar to LPS, three recombinant (r) A. americanum insulin-like growth factor binding-related proteins (rAamIGFBP-rP1, rAamIGFBP-rP6S, and rAamIGFBP-rP6L), hereafter designated as PI-rTSPs, stimulated both PBMC -derived MΦ and mice RAW 267.4 MΦ to express PI co-stimulatory markers, CD40, CD80, and CD86 and cytokines, TNFα, IL-1, and IL-6. In contrast, two A. americanum tick saliva serine protease inhibitors (serpins), AAS27 and AAS41, hereafter designated as anti-inflammatory (AI) rTSPs, on their own did not affect MΦ function or suppress expression of PI markers, but enhanced expression of AI cytokines (IL-10 and TGFβ) in MΦ that were pre-activated by LPS or PI-rTSPs. Mice paw edema test demonstrated that in vitro validated PI- and AI-rTSPs are functional in vivo since injection of HEK293-expressed PI-rTSPs (individually or as a cocktail) induced edema comparable to carrageenan-induced edema and was characterized by upregulation of CD40, CD80, CD86, TNF-α, IL-1, IL-6, and chemokines: CXCL1, CCL2, CCL3, CCL5, and CCL11, whereas the AI-rTSPs (individually and cocktail) were suppressive. We propose that the tick may utilize countervailing PI and AI TSPs to regulate evasion of host immune defenses whereby TSPs such as rAamIGFBP-rPs activate host immune cells and proteins such as AAS27 and AAS41 suppress the activated immune cells.

Several studies have documented immuno-suppressive activities in whole tick saliva and salivary gland protein extracts. We have made contribution toward understanding the molecular basis of tick feeding, as we have described functions of defined tick saliva immuno-modulatory proteins. We have shown that A. americanum injects two groups of functionally opposed tick saliva proteins: those that could counter-intuitively be characterized as pro-host defense, and those that are expected to have anti-host immune defense functions. Based on our data, we propose that the tick evades host defense using countervailing pro- and anti- inflammatory proteins in which the pro-host defense tick saliva proteins stimulate host immune cells such as macrophages, and the anti-host defense tick saliva proteins suppress functions of the activated immune cells.

Aedes aegypti saliva impairs M1-associated proinflammatory phenotype without promoting or affecting M2 polarization of murine macrophages

BACKGROUND

During the feeding process, the mouthparts of hematophagous mosquitoes break the skin barrier and probe the host tissue to find the blood. The saliva inoculated in this microenvironment modulates host hemostasis, inflammation and adaptive immune responses. However, the mechanisms involved in these biological activities remain poorly understood and few studies explored the potential roles of mosquito saliva on the individual cellular components of the immune system. Here, we report the immunomodulatory activities of Aedes aegypti salivary cocktail on murine peritoneal macrophages.

RESULTS

The salivary gland extract (SGE) of Ae. aegypti inhibited the production of nitric oxide and inflammatory cytokines such as interleukin-6 (IL-6) and IL-12, as well as the expression of inducible nitric oxide synthase and NF-κB by murine macrophages stimulated by lipopolysaccharide (LPS) plus interferon-γ (IFN-γ). The spare respiratory capacity, the phagocytic and microbicidal activities of these macrophages were also reduced by Ae. aegypti SGE. These phenotypic changes are consistent with SGE suppressing the proinflammatory program of M1 macrophages. On the other hand, Ae. aegypti SGE did not influence M2-associated markers (urea production, arginase-1 and mannose receptor-1 expression), either in macrophages alternatively activated by IL-4 or in those classically activated by LPS plus IFN-γ. In addition, Ae. aegypti SGE did not display any cytokine-binding activity, nor did it affect macrophage viability, thus excluding supposed experimental artifacts.

CONCLUSIONS

Given the importance of macrophages in a number of biological processes, our findings help to enlighten how vector saliva modulates vertebrate host immunity.

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.

An insight into the ecobiology, vector significance and control of Hyalomma ticks (Acari: Ixodidae): A review

Ticks (Acari:Ixodoidea) are important ectoparasites infesting livestock and human populations around the globe. Ticks can cause damage directly by affecting the site of infestation, or indirectly as vectors of a wide range of protozoa, bacteria and viruses which ultimately lead to lowered productivity of livestock populations. Hyalomma is a genus of hard ticks, having more than 30 species well-adapted to hot, humid and cold climates. Habitat diversity, vector ability, and emerging problem of acaricidal resistance in enzootic regions typify this genus in various countries around the world. This paper reviews the epidemiology, associated risk factors (temperature, climate, age, sex, breed etc.), vector role, vector-pathogen association, and reported control strategies of genus Hyalomma. The various proteins in saliva of Hyalomma secreted into the blood stream of host and the prolonged attachment are responsible for the successful engorgement of female ticks in spite of host immune defense system. The various immunological approaches that have been tried by researchers in order to cause tick rejection are also discussed. In addition, the novel biological control approaches involving the use of entomo-pathogenic nematodes and Bacillus thuringiensis (B. thuringiensis) serovar thuringiensis H14; an endotoxin, for their acaricidal effect on different species and life cycle stages of Hyalomma are also presented.

Hematobin is a novel immunomodulatory protein from the saliva of the horn fly Haematobia irritans that inhibits the inflammatory response in murine macrophages

Background

The horn fly Haematobia irritans is a blood-sucking ectoparasite responsible for substantial economic loss of livestock. Like other hematophagous arthropods species, the successful blood-feeding of H. irritans is highly dependent on the modulation of the host’s hemostasis and immune system. Here, we evaluated the biological activity of hematobin (HTB), a protein recently identified in the H. irritans saliva, on macrophage biology. The goal was to understand the putative interactions between the components of H. irritans saliva and the early host immune responses.

Results

Thioglycolate-elicited peritoneal macrophages from BALB/c mice were stimulated by lipopolysaccharide (LPS) plus interferon-γ (IFN-γ) in the presence or absence of recombinant HTB. The presence of the salivary protein in the cultures inhibited nitric oxide production and decreased the inducible nitric oxide synthase (iNOS) expression induced by LPS plus IFN-γ. The tumor necrosis factor-α (TNF-α) and interleukin-12p40 (IL-12p40) levels were also reduced in the macrophages pre-incubated with HTB; these findings correlated to the decreased NF-κB expression. The biological activities described here were not associated with changes in annexin V binding to macrophages suggesting that HTB does not induce cell death. In addition, the activity of HTB seems to be specific to macrophages because no changes were observed in lymphocyte proliferation or cytokine production.

Conclusions

We describe here the first bioactive salivary protein of H. irritans. We characterized its ability to modulate macrophage inflammatory response, and the results can help explain how horn flies modulate the host immune system to feed on blood.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3017-z) contains supplementary material, which is available to authorized users.

Interaction between saliva's adenosine and tick parasitism: effects on feeding and reproduction

Background

It has recently been demonstrated that saliva from Rhipicephalus sanguineus ticks contains adenosine (ADO) and prostaglandin E2 (PGE2), two non-protein molecules that have significant immunomodulatory properties. These molecules can inhibit cytokine production by dendritic cells (DCs), while also reducing the expression of CD40 in these cells. However, more studies are needed for a better understanding of their participation in the feeding of ticks in vivo. This work, therefore, evaluated the importance of ADO during tick infestations. Mice were infested with adult ticks (3 couples/mouse), and their skin was collected at the tick-infested site (3rd and 7th day), and mRNA for receptors of ADO was quantified by real-time PCR.

Results

Tick infestation increased by four and two times the expression of the A2b and A3v1 receptors on day 3, respectively, while expression of other ADO receptors was unaltered. In addition, we treated mice (n = 10/group) daily with 8-(p-Sulfophenyl)theophylline, 8-pSPT, 20 mg/kg, i.p.), a non-selective antagonist of ADO receptors, and evaluated the performance of ticks during infestations. Female ticks fed on 8-pSPT-treated mice presented a reduction in their engorgement, weight and hatching rates of egg masses, and survival times of larvae compared to the same parameters presented by ticks in the control group. To investigate if these 8-pSPT-treated mice presented altered immune responses, we performed three tick infestations and collected their lymph node cells to determine the percentages and activation state of DCs and cytokine production by lymphocytes by flow cytometry (Cytometric Bead Array technique, CBA). Our data showed that 8-pSPT-treated mice presented an increase in the percentage of DCs as well as of their stimulatory and co-stimulatory molecules (CD40, CD80 and MHCII). Regarding production of T cell cytokines, we observed a significant increase in the levels of IL-2 and a significant decrease in IL-10, IL-17, TNF-α and IFN-γ cytokines.

Conclusions

These results suggest that ADO produced by ticks helps them feed and reproduce and that this effect may be due to modulation of host DCs and T cells.

Deltamethrin as inductor agent of precocious ovarian degeneration in Rhipicephalus sanguineus s.l. (Acari: Ixodidae) ticks

The cosmopolitan species Rhipicephalus sanguineus s.l. is one of the most widely distributed ticks all over the world. These ectoparasites are vectors of several pathogens and cause significant direct damage to their hosts. The biological success of these ectoparasites has been attributed to their ovaries and salivary glands, organs that ensure their survival in various environmental conditions. The importance of the ovaries in ticks is that, after mating, the individuals are able to lay approximately three thousand eggs. The present study had the objective to demonstrate the effects of deltamethrin obtained from the product Butox P CE 25^® (MSD Saúde Animal, São Paulo, Brazil) on the ovarian development of R. sanguineus s.l. females. The chemical was tested in the concentrations of 25, 50, 100 and 200 ppm (respectively 80, 40, 20 and 10 times lower than the recommended by the manufacturer). Through the application of histological techniques and HE staining, the results showed that the deltamethrin was potentially able to modify the morphophysiology of the oocytes in all developmental stages, interfering in the vitellogenesis, causing intense vacuolation, cytoplasmic disorganization, and alterations in the chorion secretion. In addition, the chemical affected the germ vesicle of some oocytes, causing damages and hypertrophy, fragmenting the chromatin and forming bodies strongly stained by hematoxylin. Therefore, this study confirmed that the deltamethrin had an important action on the reproductive system of the R. sanguineus s.l. females, causing the precocious structural disorganization of the germ cells, consequently preventing the generation of new individuals.

Virulence of recurrent infestations with Borrelia-infected ticks in a Borrelia-amplifying bird

Lyme disease cases caused by Borrelia burgdorferi s.l. bacteria is increasing steadily in Europe, in part due to the expansion of the vector, Ixodes ricinus. Wild reservoir hosts are typically recurrently infested. Understanding the impact of these cumulative parasite exposures on the host's health is, therefore, central to predict the distribution of tick populations and their pathogens. Here, we have experimentally investigated the symptoms of disease caused by recurrent infestations in a common songbird (Parus major). Birds were exposed three times in succession to ticks collected in a Borrelia endemic area. Health and immune measures were analyzed in order to investigate changes in response to tick infestation and Borrelia infection rate. Nitric oxide levels increased with the Borrelia infection rate, but this effect was increasingly counteracted by mounting tick infestation rates. Tick infestations equally reduced haematocrit during each cycle. But birds overcompensated in their response to tick feeding, having higher haematocrit values during tick-free periods depending on the number of ticks they had been previously exposed to. Body condition showed a similar overshooting response in function of the severity of the Borrelia infection. The observed overcompensation increases the bird's energetic needs, which may result in an increase in transmission events.

Modulation of host immunity by tick saliva

Next generation sequencing and proteomics have helped to comprehensively characterize gene expression in tick salivary glands at both the transcriptome and the proteome level. Functional data are, however, lacking. Given that tick salivary secretions are critical to the success of the tick transmission lifecycle and, as a consequence, for host colonization by the pathogens they spread, we thoroughly review here the literature on the known interactions between tick saliva (or tick salivary gland extracts) and the innate and adaptive vertebrate immune system. The information is intended to serve as a reference for functional characterization of the numerous genes and proteins expressed in tick salivary glands with an ultimate goal to develop novel vector and pathogen control strategies.

SIGNIFICANCE

We overview all the known interactions of tick saliva with the vertebrate immune system. The provided information is important, given the recent developments in high-throughput transcriptomic and proteomic analysis of gene expression in tick salivary glands, since it may serve as a guideline for the functional characterization of the numerous newly-discovered genes expressed in tick salivary glands.

Partial pathogen protection by tick-bite sensitization and epitope recognition in peptide-immunized HLA DR3 transgenic mice

Ticks are notorious vectors of disease for humans, and many species of ticks transmit multiple pathogens, sometimes in the same tick bite. Accordingly, a broad-spectrum vaccine that targets vector ticks and pathogen transmission at the tick/host interface, rather than multiple vaccines against every possible tickborne pathogen, could become an important tool for resolving an emerging public health crisis. The concept for such a tick protective vaccine comes from observations of an acquired tick resistance (ATR) that can develop in non-natural hosts of ticks following sensitization to tick salivary components. Mice are commonly used as models to study immune responses to human pathogens but normal mice are natural hosts for many species of ticks and fail to develop ATR. We evaluated HLA DR3 transgenic (tg) "humanized" mice as a potential model of ATR and assessed the possibility of using this animal model for tick protective vaccine discovery studies. Serial tick infestations with pathogen-free Ixodes scapularis ticks were used to tick-bite sensitize HLA DR3 tg mice. Sensitization resulted in a cytokine skew favoring a Th2 bias as well as partial (57%) protection to infection with Lyme disease spirochetes (Borrelia burgdorferi) following infected tick challenge when compared to tick naïve counterparts. I. scapularis salivary gland homogenate (SGH) and a group of immunoinformatic-predicted T cell epitopes identified from the I. scapularis salivary transcriptome were used separately to vaccinate HLA DR3 tg mice, and these mice also were assessed for both pathogen protection and epitope recognition. Reduced pathogen transmission along with a Th2 skew resulted from SGH vaccination, while no significant protection and a possible T regulatory bias was seen in epitope-vaccinated mice. This study provides the first proof-of-concept for using HLA DR tg "humanized" mice for studying the potential tick protective effects of immunoinformatic- or otherwise-derived tick salivary components as tickborne disease vaccines.

A Tick Vector Transmission Model of Monocytotropic Ehrlichiosis

BACKGROUND

Ehrlichioses are emerging, tick-borne diseases distributed worldwide. Previously established animal models use needle inoculation as a mode of infection; however, there is limited representation of natural transmission in artificially inoculated models compared with transmission by the tick vector. The objective of this study was to develop a tick vector transmission animal model of ehrlichial infection using a human pathogen, Ehrlichia muris-like agent (EMLA).

METHODS

Ixodes scapularis larvae were fed on EMLA-infected mice, and after molting, infected nymphs were used to infest naive animals.

RESULTS

Ehrlichiae were acquired by 90%-100% of feeding larvae. The majority of animals fed upon by infected nymphs developed sublethal infection with 27% lethality. Bacteria disseminated to all tissues tested with greatest bacterial loads in lungs, but also spleen, lymph nodes, liver, kidneys, brain, and bone marrow. Numerous foci of cellular infiltration, mitoses, and hepatocellular death were observed in liver. Mice infected by tick transmission developed higher antiehrlichial antibody levels than needle-inoculated animals. Tick-feeding-site reactions were observed, but there was no observed difference between animals infested with infected or uninfected ticks.

CONCLUSIONS

For the first time we were able to develop a tick transmission model with an Ehrlichia that is pathogenic for humans.

Signatures of resistance to Lepeophtheirus salmonis include a TH2-type response at the louse-salmon interface

Disease outbreaks with the salmon louse Lepeophtheirus salmonis cause significant economic losses in mariculture operations worldwide. Variable innate immune responses at the louse-attachment site contribute to differences in susceptibility among species such that members of Salmo spp. are more susceptible to infection than those of some Oncorhynchus spp. Relatively little is known about the mechanisms that contribute to disease resistance or susceptibility to L. salmonis in salmon. Here, we utilize histochemistry and transcriptomics in a comparative infection model with susceptible (Atlantic, sockeye) and resistant (coho) salmon. At least three cell populations (MHIIβ+, IL1β+, TNFα+) were activated in coho salmon skin during L. salmonis infection. Locally elevated expression of several pro-inflammatory mediators (e.g. IL1β, IL8, TNFα, COX2, C/EBPβ), and tissue repair enzymes (MMP9, MMP13) were detected in susceptible and resistant species. However, responses specific to coho salmon (e.g. IL4, IL6, TGFβ) or responses shared among susceptible salmon (e.g. SAP, TRF, Cath in Atlantic and sockeye salmon) provide evidence for species-specific pathways contributing to resistance or susceptibility, respectively. Our results confirm the importance of an early pro-inflammatory TH1-type pathway as an initial host response during infection with Pacific sea lice, and demonstrate subsequent regulatory TH2-type processes as candidate defense mechanisms in the skin of resistant coho salmon.

Meta-analysis of the effects of insect vector saliva on host immune responses and infection of vector-transmitted pathogens: a focus on leishmaniasis

A meta-analysis of the effects of vector saliva on the immune response and progression of vector-transmitted disease, specifically with regard to pathology, infection level, and host cytokine levels was conducted. Infection in the absence or presence of saliva in naïve mice was compared. In addition, infection in mice pre-exposed to uninfected vector saliva was compared to infection in unexposed mice. To control for differences in vector and pathogen species, mouse strain, and experimental design, a random effects model was used to compare the ratio of the natural log of the experimental to the control means of the studies. Saliva was demonstrated to enhance pathology, infection level, and the production of Th2 cytokines (IL-4 and IL-10) in naïve mice. This effect was observed across vector/pathogen pairings, whether natural or unnatural, and with single salivary proteins used as a proxy for whole saliva. Saliva pre-exposure was determined to result in less severe leishmaniasis pathology when compared with unexposed mice infected either in the presence or absence of sand fly saliva. The results of further analyses were not significant, but demonstrated trends toward protection and IFN-γ elevation for pre-exposed mice.

Arthropod vectors transmit a wide variety of diseases resulting in substantial human morbidity and economic costs worldwide. When hematophagous arthropods blood feed, they release saliva into the host. This saliva elicits a strong immune response and has recently been a focus for vaccine research. There is evidence that the saliva enhances infection in naïve hosts, but that prior exposure to saliva results in less severe infection. This analysis endeavored to determine whether there was a statistically significant enhancement or protective effect with regard to saliva exposure and the progression of disease, and to determine the underlying immune mechanism driving these effects. We found that saliva does indeed enhance infection levels of vector-transmitted pathogens and leishmaniasis pathology in naïve mice and elevates Th2 cytokine levels (IL-4 and IL-10). We also determined that pre-exposure to saliva results in less severe pathology of experimental leishmaniasis in mice. These results are important for vaccine trials and vector control programs, though more studies are needed with regard to pre-exposure.

Proteome of Rhipicephalus sanguineus tick saliva induced by the secretagogues pilocarpine and dopamine

One dimensional gel electrophoresis was used to separate proteins from the saliva of Rhipicephalus sanguineus female ticks fed on rabbits. Gel slices were subjected to tryptic digestion and analyzed by reversed-phase HPLC followed by MS/MS analysis. The data were compared to a database of salivary proteins of the same tick and to the predicted proteins of the host. Saliva was obtained by either pilocarpine or dopamine stimulation of partially fed ticks. Electrophoretic separations of both yielded products that were identified by mass spectrometry, although the pilocarpine-derived sample was of much better quality. The majority of identified proteins were of rabbit origin, indicating the recycling of the host proteins in the tick saliva, including hemoglobin, albumin, haptoglobin, transferring, and a plasma serpin. The few proteins found that were previously associated with parasitism and blood feeding include 2 glycine-rich, cement-like proteins, 2 lipocalins, and a thyropin protease inhibitor. Among other of the 19 tick proteins identified, albeit with undefined roles, were SPARC and cyclophilin A. This catalog provides a resource that can be mined for secreted molecules that play a role in tick-host interactions.

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.

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.

Rhipicephalus microplus salivary gland molecules induce differential CD86 expression in murine macrophages

Background

Tick parasitism is a major impediment for cattle production in many parts of the world. The southern cattle tick, Rhipicephalus (Boophilus) microplus, is an obligate hematophagous parasite of domestic and wild animals that serves as vector of infectious agents lethal to cattle. Tick saliva contains molecules evolved to modulate host innate and adaptive immune responses which facilitates blood feeding and pathogen transmission. Tick feeding promotes CD4 T cell polarization to a Th2 profile usually accompanied by down-regulation of Th1 cytokines through as yet undefined mechanisms. Co-stimulatory molecules on antigen presenting cells are central to development of T cell responses including Th1 and Th2 responses. Tick induced changes to antigen presenting cell signal transduction pathways are largely unknown. Here we document the ability of R. microplus salivary gland extracts (SGE) to effect differential CD86 expression.

Results

We examined changes in co-stimulatory molecule expression in murine RAW 264.7 cells in response to R. microplus SGE exposure in the presence of the toll-like receptor 4 (TLR4) ligand, LPS. After 24 hrs, CD86, but not CD80, was preferentially up-regulated on mouse macrophage RAW 264.7 cells when treated with SGE and then LPS, but not SGE alone. CD80 and CD40 expression was increased with LPS, but the addition of SGE did not alter expression. Higher concentrations of SGE were less effective at increasing CD86 RNA expression. The addition of mitogen or extracellular kinase (MEK) inhibitor, PD98059, significantly reduced the ability for SGE to induce CD86 expression, indicating activation of MEK is necessary for SGE induced up-regulation.

Conclusions

Molecules in SGE of R. microplus have a concentration-dependent effect on differential up-regulation of CD86 in a macrophage cell line activated by the TLR4 ligand, LPS. This CD86 up-regulation is at least partially dependent on the ERK1/2 pathway and may serve to promote Th2 polarization of the immune response.

An insight into the sialotranscriptome of the brown dog tick, Rhipicephalus sanguineus

BACKGROUND

Rhipicephalus sanguineus, known as the brown dog tick, is a common ectoparasite of domestic dogs and can be found worldwide. R.sanguineus is recognized as the primary vector of the etiological agent of canine monocytic ehrlichiosis and canine babesiosis. Here we present the first description of a R. sanguineus salivary gland transcriptome by the production and analysis of 2,034 expressed sequence tags (EST) from two cDNA libraries, one consctructed using mRNA from dissected salivary glands from female ticks fed for 3-5 days (early to mid library, RsSGL1) and the another from ticks fed for 5 days (mid library, RsSGL2), identifying 1,024 clusters of related sequences.

RESULTS

Based on sequence similarities to nine different databases, we identified transcripts of genes that were further categorized according to function. The category of putative housekeeping genes contained approximately 56% of the sequences and had on average 2.49 ESTs per cluster, the secreted protein category contained 26.6% of the ESTs and had 2.47 EST's/clusters, while 15.3% of the ESTs, mostly singletons, were not classifiable, and were annotated as "unknown function". The secreted category included genes that coded for lipocalins, proteases inhibitors, disintegrins, metalloproteases, immunomodulatory and antiinflammatory proteins, as Evasins and Da-p36, as well as basic-tail and 18.3 kDa proteins, cement proteins, mucins, defensins and antimicrobial peptides. Comparison of the abundance of ESTs from similar contigs of the two salivary gland cDNA libraries allowed the identification of differentially expressed genes, such as genes coding for Evasins and a thrombin inhibitor, which were over expressed in the RsSGL1 (early to mid library) versus RsSGL2 (mid library), indicating their role in inhibition of inflammation at the tick feeding site from the very beginning of the blood meal. Conversely, sequences related to cement (64P), which function has been correlated with tick attachment, was largely expressed in the mid library.

CONCLUSIONS

Our survey provided an insight into the R. sanguineus sialotranscriptome, which can assist the discovery of new targets for anti-tick vaccines, as well as help to identify pharmacologically active proteins.

Histopathology of Rhipicephalus sanguineus (Acari: Ixodidae) ticks fed on resistant hosts

Histological features of Rhipicephalus sanguineus ticks fed on dog, a non resistant host, and on guinea pig, a resistant host, were compared. Unfed ticks and ticks from each host species were collected during first and third infestation and processed for histology. Many ticks from guinea pigs, especially during third infestation, were unattached, dehydrated and small. Only the midgut of ticks fed on guinea pigs had host leukocytes. Vacuolization of midgut cells was observed in all ticks, with exception of those fed on dogs for more than 96 h. Ticks of guinea pigs, particularly from third infestation, had vacuolated tracheae and swelling of malpighian tubules. Solely ticks from third infestation of guinea pigs displayed vacuolization of oocytes. Ticks fed on guinea pigs also had an increased number of guanine spherules. Observed alterations in ticks from guinea pigs are discussed.

The CCL3/macrophage inflammatory protein-1alpha-binding protein evasin-1 protects from graft-versus-host disease but does not modify graft-versus-leukemia in mice

CCL3 is a protein of the CC chemokine family known to be important for T cell recruitment in inflammatory diseases. The aim of the current study was to evaluate the effects and putative mechanism of action of evasin-1, a novel CCL3-binding protein, in the pathogenesis of acute graft-versus-host disease (GVHD). GVHD was induced by the transplantation of splenocytes from C57BL/6J to B6D2F1 mice. Treatment of recipient mice with evasin-1 prevented mortality associated with GVHD. This was correlated with reduced weight loss and clinical disease severity. Analysis of the small intestine showed that evasin-1 treatment reduced the histopathological score and decreased levels of IFN-gamma and CCL5. Mechanistically, evasin-1 treatment reduced the number of CD4(+) and CD8(+) T cells infiltrating the small intestine, as assessed by immunohistochemistry, and the adhesion of leukocytes to intestinal venules of recipient mice, as assessed by intravital microscopy. Evasin-1 was also able to decrease liver damage, as seen by reduction of inflammatory infiltrate and IFN-gamma levels. Treatment with evasin-1 did not interfere with graft-versus-leukemia. Altogether, our studies demonstrate that CCL3 plays a major role in mediating GVHD, but not graft-versus-leukemia in mice and suggest that blockade of CCL3 with evasin-1 has potential therapeutic application in patients undergoing bone marrow transplantation.

Biological parameters of larvae, nymphs, and engorged females of Amblyomma cajennense (Fabricius, 1787) (Acari: Ixodidae) obtained from artificial and successive infestations on Oryctolagus cuniculus (Linnaeus, 1758) (Lagomorpha: Ochotonidae)

The development of acquired resistance to Amblyomma cajennense ticks was evaluated. A total of 18 rabbits were uniformly distributed into three groups named GL, GN, and GA that were submitted to three consecutive infestations with, respectively, larvae, nymphs, and adults of A. cajennense. After the infestations, the parasitic and reproductive parameters of recovered instars were evaluated. A significant reduction of recovery rates of inoculated ticks was observed only after the third infestation of animals in groups GL and GN (P<0.01). The modal day for drop-off of engorged larvae and nymphs increased along the infestations. The recovered engorged nymphs presented a significant reduction of the mean body weight between the first and the third infestations (P<0.01). A significant reduction in the mean recovery rate of engorged females was only observed during the third infestation. However, significant reductions (P<0.05) in body weight, egg mass weight, and larva eclosions were observed for recovered engorged females after the second infestation onwards. The results suggest the occurrence of resistance of rabbits to A. cajennense infestations, being more evident against the adult stage.

Tick saliva induces regulatory dendritic cells: MAP-kinases and Toll-like receptor-2 expression as potential targets

Ticks (Acari: Ixodidae) are bloodsucking ectoparasitic arthropods of human and veterinary medical importance. Tick saliva has been shown to contain a wide range of bioactive molecules with vasodilatory, antihemostatic, and immunomodulatory activities. We have previously demonstrated that saliva from Rhipicephalus sanguineus ticks inhibits the maturation of dendritic cells (DCs) stimulated with LPS. Here we examined the mechanism of this immune subversion, evaluating the effect of tick saliva on Toll-like receptor (TLR)-4 signalling pathway in bone marrow-derived DCs. We demonstrated that R. sanguineus tick saliva impairs maturation of DCs stimulated with LPS, a TLR-4 ligand, leading to increased production of interleukin (IL)-10 and reduced synthesis of IL-12p70 and TNF-alpha. The immunomodulatory effect of the tick saliva on the production of pro-inflammatory cytokines by DCs stimulated with LPS was associated with the observation that tick saliva inhibits the activation of the ERK 1/2 and p38 MAP kinases. These effects were independent of the expression of TLR-4 on the surface of DCs. Additionally, saliva-treated DCs also presented a similar pattern of cytokine modulation in response to other TLR ligands. Since the recent literature reports that several parasites evade immune responses through TLR-2-mediated production of IL-10, we evaluated the effect of tick saliva on the percentage of TLR-2(+) DCs stimulated with the TLR-2 ligand lipoteicoic acid (LTA). The data showed that the population of DCs expressing TLR-2 was significantly increased in DCs treated with LTA plus saliva. In addition, tick saliva alone increased the expression of TLR-2 in a dose- and time-dependent manner. Our data suggest that tick saliva induces regulatory DCs, which secrete IL-10 and low levels of IL-12 and TNF-alpha when stimulated by TLR ligands. Such regulatory DCs are associated with expression of TLR-2 and inhibition of ERK and p38, which promotes the production of IL-10 and thus down-modulates the host's immune response, possibly favouring susceptibility to tick infestations.

Natural history of Ehrlichia ruminantium

Ehrlichia ruminantium is an obligately intracellular proteobacterium which causes a disease known as heartwater or cowdriosis in some wild, and all domestic, ruminants. The organism is transmitted by ticks of the genus Amblyomma, and it is of serious economic importance wherever the natural vectors occur, an area which includes all of sub-Saharan Africa, and several islands in the Caribbean. The disease was first recognized in South Africa in the 19th century, where its tick-borne nature was determined in 1900, but the organism itself was not demonstrated until 1925, when it was recognized to be a rickettsia, initially named Rickettsia ruminantium. It was thus the first species of what are now known as Ehrlichia to be discovered, and most of the early work to elucidate the nature of the organisms, and its reservoirs and vectors, was performed in South Africa. The next milestone was the development, in 1945, of an infection and treatment regimen to immunize livestock, and this is still the only commercially available "vaccine" against the disease. Then in 1985, after fruitless attempts over many years, the organism was propagated reliably in tissue culture, opening the way for the first application of the newly developed techniques of molecular genetics. From 1990 onwards the pace of heartwater research accelerated rapidly, with notable advances in phylogeny, diagnosis, epidemiology, immunology, and vaccine development. The complete genome sequence was published in 2005, and during the last two years a new understanding has arisen of the remarkable genetic variability of the organism and new experimental vaccines have been developed. Despite all this the goal of producing an effective vaccine against the disease in the field still remains frustratingly just beyond reach. This article summarises our current understanding of the nature of E. ruminantium, at a time when the prospects for the development of an effective vaccine against the organism seem better than at any time since its discovery 83 years ago.

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.

Langerhans cell deficiency impairs Ixodes scapularis suppression of Th1 responses in mice

Ixodes scapularis ticks transmit a number of human pathogens, including the Lyme disease spirochete Borrelia burgdorferi. I. scapularis suppresses host immunity in the skin to promote feeding and systemically skew T-helper (Th)-cell differentiation toward Th2 cells in secondary lymphoid organs. Although components of tick saliva are known to influence Th-cell polarization, the mechanism whereby tick feeding in the skin modulates regional and systemic Th-cell responses is unknown. In this study, the role of the epidermal Langerhans cell (LC) subset of skin dendritic cells in tick-mediated Th1/Th2-cell immunomodulation was assessed. Mice deficient in LCs (Langerin-DTA mice) exhibited enhanced lymph node (LN) concanavalin A (ConA)-induced Th1 responses after tick infestation in comparison to results for uninfested Langerin-DTA or wild-type (WT) mice, whereas effects on Th2-cell production of interleukin 4 were more variable. Nonetheless, the altered T-cell response did not impact tick feeding or refeeding. Gamma interferon production by ConA-stimulated LN cells of both WT and LC-deficient mice was enhanced by as much as fourfold after B. burgdorferi-infected-tick feeding, indicating that immunomodulatory effects of tick saliva were not able to attenuate the Th1 immune responses induced by this pathogen. Taken together, these findings show a requirement for LCs in the tick-mediated attenuation of Th1 responses in regional lymph nodes but not in the spleens of mice and show that the presence of a pathogen can overcome the Th1-inhibitory effects of tick feeding on the host.

Effect of Amblyomma cajennense ticks on the immune response of BALB/c mice and horses

This work evaluated the effect of the Amblyomma cajennense tick on the immune response of BALB/c mice and on horse lymph node cell proliferation. We observed that mice do not develop resistance to nymphs of this tick species and that lymphocyte proliferation of this host is inhibited by tick saliva, nymphal extract, or infestations. Horse lymph node cell proliferation is inhibited by tick saliva as well. Mice lymphocytes under the effect of tick saliva, nymphal extract, or infestations display a predominantly Th-2 cytokine production pattern. Observed results partially explain this tick's disease vectoring capacity and broad host range.

Tick saliva affects both proliferation and distribution of Borrelia burgdorferi spirochetes in mouse organs and increases transmission of spirochetes to ticks

Ixodes ricinus tick saliva-activated transmission of Borrelia burgdorferi sensu stricto spirochetes was studied on the C3H/HeN mouse model. The influence of the feeding of uninfected nymphs on the proliferation and distribution of intradermally inoculated spirochetes was compared with the effect of co-inoculated saliva or salivary gland extract (SGE), respectively. Spirochete loads in murine tissues were evaluated using real-time q-PCR. SGE induced significantly increased spirochete numbers in the skin on the days 4 and 6 post-infection (p.i.). On the other hand, decreased bacterial load in the heart of SGE-treated mice was demonstrated in comparison with control animals. The inoculation of tick saliva increased spirochete load in the urinary bladder on day 6 p.i., while the number of spirochetes in the heart declined on day 6 p.i. The feeding of I. ricinus nymphs raised the spirochete load in the bladder on the days 4 and 6 p.i. On day 6, the number of spirochetes found in the heart was significantly lower than in controls. The prevalence of spirochetes in ticks infected by feeding on mice was more than 10 times higher when the mice were infected with the mixture of spirochetes and saliva or SGE, in comparison with spirochetes alone. The presence of SGE in the infectious inoculum increased the spirochete burden per tick from 0 to almost 28,000. Taken together, these results show a very early effect of tick saliva on the proliferation and distribution of Borrelia spirochetes in the host, probably due to the effect of saliva on the host innate immunity mechanisms.

The immunosuppresive tick salivary protein, Salp15

The interaction between Ixodid ticks and their mammalian hosts is a complex relationship. While the mammalian host tries to avoid the completion of the feeding process, the tick has devised strategies to counteract these attempts. Tick saliva contains a vast array of pharmacological activities that presumably aid the tick to evade host responses, including anticomplement, oxidative and innate and adaptive immune responses. The characterization of these activities has gained momentum in the last several years. One of the best studied activities present in tick saliva corresponds to the antigen known as Salp15, which binds specifically to the T-cell coreceptor CD4 resulting in the specific repression of CD4+ T-cell activation. We discuss here the current state of our knowledge of the mode of action of this salivary protein.

Tick saliva inhibits dendritic cell migration, maturation, and function while promoting development of Th2 responses

Similarly to other blood-feeding arthropods, ticks have evolved immunosuppressive mechanisms enabling them to overcome the host immune system. Although the immunomodulatory effect of tick saliva on several cell populations of the immune system has been extensively studied, little is known about its impact on dendritic cells (DCs). We have examined the effect of Ixodes ricinus tick saliva on DC function in vitro and in vivo. Exposure of DCs to tick saliva in vitro resulted in impaired maturation, upon CD40 or TLR9, TLR3 and TLR7 ligation, as well as reduced Ag presentation capacity. Administration of tick saliva in vivo significantly inhibited maturation and early migration of DCs from inflamed skin to draining lymph nodes, and decreased the capacity of lymph node DCs to present soluble Ag to specific T cells. Moreover, saliva-exposed DCs failed to induce efficient Th1 and Th17 polarization and promoted development of Th2 responses. Our data reveal a complex inhibitory effect exerted by tick saliva on DC function. Given the role of DCs as the key instigators of adaptive immune responses, alteration of their function might represent a major mechanism of tick-mediated immune evasion.

The brown dog tick, Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae): from taxonomy to control

Rhipicephalus sanguineus, commonly known as the brown dog tick, is a three-host tick that feeds primarily on dogs and occasionally on other hosts, including humans. R. sanguineus ticks are widely distributed around the world and they are known vectors of pathogens, such as Babesia canis, Ehrlichia canis, and Rickettsia conorii. The increasing number of cases of human parasitism by R. sanguineus ticks reported in the literature indicates that the interaction between humans and R. sanguineus ticks may be more common than it is actually recognized. The indiscriminate use of acaricides is an emerging problem worldwide and has led to the selection of acaricide resistant tick strains. In this article, the medical and veterinary importance, taxonomy, biology, and ecology of R. sanguineus ticks around the world are reviewed. It also discusses the current strategies for the control of R. sanguineus, highlighting the potential risks associated to the improper use of acaricides, such as environmental pollution and toxicity to humans and other non-target organisms (e.g., tick predators).

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.

Lepeophtheirus salmonis secretory/excretory products and their effects on Atlantic salmon immune gene regulation

We have previously shown that Lepeophtheirus salmonis produces trypsin and prostaglandin E(2) (PGE(2)) that are most likely responsible for the limited inflammatory response of Atlantic salmon to infection. After removal of the dopamine and PGE(2), the immunomodulatory activity of unfractionated and pools of the fractionated secretions was determined by examining the effects of the secretions on Atlantic salmon immune gene expression. Incubation of macrophage-enriched isolates of Atlantic salmon head kidney cells with the unfractionated secretion + PGE(2) revealed a significant inhibition of interleukin-1beta (IL-1beta) and major histocompatibility class I gene expression. Inhibition of lipopolysaccharide-induced IL-1beta expression in the Atlantic salmon head kidney cell line (SHK-1) was observed when three pools of the secretory/excretory products were tested. Further purification of products within these pools revealed that fraction 1-2 could account fully for the inhibition of IL-1beta expression in SHK-1 cells observed in pooled fraction 1. This study demonstrates that there are other immunomodulatory compounds produced by L. salmonis, in addition to PGE(2) and trypsin, that can inhibit the expression of Atlantic salmon immune-related genes in vitro.

Cutting edge: CD4 is the receptor for the tick saliva immunosuppressor, Salp15

Salp15 is an Ixodes scapularis salivary protein that inhibits CD4+ T cell activation through the repression of TCR ligation-triggered calcium fluxes and IL-2 production. We show in this study that Salp15 binds specifically to the CD4 coreceptor on mammalian host T cells. Salp15 specifically associates through its C-terminal residues with the outermost two extracellular domains of CD4. Upon binding to CD4, Salp15 inhibits the subsequent TCR ligation-induced T cell signaling at the earliest steps including tyrosine phosphorylation of the Src kinase Lck, downstream effector proteins, and lipid raft reorganization. These results provide a molecular basis to understanding the immunosuppressive activity of Salp15 and its specificity for CD4+ T cells.

Transcriptome analysis of the salivary glands of Dermacentor andersoni Stiles (Acari: Ixodidae)

Amongst blood-feeding arthropods, ticks of the family Ixodidae (hard ticks) are vectors and reservoirs of a greater variety of infectious agents than any other ectoparasite. Salivary glands of ixodid ticks secrete a large number of pharmacologically active molecules that not only facilitate feeding but also promote establishment of infectious agents. Genomic, proteomic and immunologic characterization of bioactive salivary gland molecules are, therefore, important as they offer new insights into molecular events occurring at the tick-host interface and they have implications for development of novel control strategies. The present work uses complementary DNA (cDNA) sequence analysis to identify salivary gland transcripts expressed by the Rocky Mountain wood tick, Dermacentor andersoni, a vector of the human pathogens causing Rocky Mountain spotted fever, Colorado tick fever, tularemia, and Powassan encephalitis as well as the veterinary pathogen Anaplasma marginale. Dermacentor andersoni is also capable of inducing tick paralysis. Automated single-pass DNA sequencing was conducted on 1440 randomly selected cDNA clones from the salivary glands of adult female D. andersoni collected during the early stages of feeding (18-24h). Analysis of the expressed sequence tags (ESTs) resulted in 544 singletons and 218 clusters with more than one quality read and attempts were made to assign putative functions to tick genes based on amino acid identity to published protein databases. Approximately 25.6% (195) of the sequences showed limited or no homology to previously identified gene products. A number of novel sequences were identified which presented significant sequence similarity to mammalian genes normally associated with extracellular matrix (ECM), regulation of immune responses, tumor suppression, and wound healing. Several coding sequences possessed various degrees of homology to previously described proteins from other tick species. Preliminary nucleotide variation analysis of these and other tick sequences suggests extensive nucleotide diversity, which has implications for evolution of tick feeding. Intra-species diversity studies can be a promising tool for identifying sequence variations potentially associated with phenotypic traits affecting vector-host-pathogen interactions.

Differential clearance and immune responses to tick cell-derived versus macrophage culture-derived Ehrlichia chaffeensis in mice

Human monocytic ehrlichiosis is caused by a tick-transmitted rickettsia, Ehrlichia chaffeensis. We recently reported that E. chaffeensis grown in tick cells expresses different proteins than bacteria grown in macrophages. Therefore, we tested the hypothesis that immune responses against E. chaffeensis would be different if the mice are challenged with bacteria grown in macrophages or tick cells. We assessed the E. chaffeensis clearance from the peritoneum, spleen, and liver by C57BL/6J mice using a TaqMan-based real-time reverse transcription-PCR assay. Macrophage-grown E. chaffeensis was cleared in 2 weeks from the peritoneum, whereas the pathogen from tick cells persisted for nine additional days and included three relapses of increasing bacterial load separated by three-day intervals. Tick cell-grown bacteria also persisted in the livers and spleens with higher bacterial loads compared to macrophage-grown bacteria and fluctuated over a period of 35 days. Three-day periodic cycles were detected in T-cell CD62L/CD44 ratios in the spleen and bone marrow in response to infections with both tick cell- and macrophage-grown bacteria and were accompanied by similar periodic cycles of spleen cell cytokine secretions and nitric oxide and interleukin-6 by peritoneal macrophages. The E. chaffeensis-specific immunoglobulin G response was considerably higher and steadily increased in mice infected with the tick cell-derived E. chaffeensis compared to DH82-grown bacteria. In addition, antigens detected by the immunoglobulins were significantly different between mice infected with the E. chaffeensis originating from tick cells or macrophages. The differences in the immune response to tick cell-grown bacteria compared to macrophage-grown bacteria reflected a delay in the shift of gene expression from the tick cell-specific Omp 14 gene to the macrophage-specific Omp 19 gene. These data suggest that the host response to E. chaffeensis depends on the source of the bacteria and that this experimental model requires the most natural inoculum possible to allow for a realistic understanding of host resistance.

Anti-tick vaccines

There is now abundant evidence that vaccination with defined protein antigens is able to induce significant immunity to tick infestation. In a limited number of cases, this immunity has been duplicated by vaccination with recombinant antigens, a critical step on the pathway to commercial vaccine production. The existence of two commercial vaccines has allowed a number of field studies showing that the existing products can make an important contribution to an integrated approach to the control of ticks in the field. Under most circumstances however, the use of a tick vaccine as the single, stand alone control technology is likely to require more efficacious vaccines than those currently available. Increases in efficacy are most likely to come through the discovery of additional, effective vaccine antigens. The number of antigens with demonstrated effect is increasing, though only slowly, while the number of potential antigens that remain to be evaluated is increasing more quickly. There is limited, though convincing, evidence that some of these antigens will show effective cross-species protection, though in a poorly understood and unpredictable way. The groundwork has been laid; the potential of the field is still to be effectively exploited.

The immunomodulatory factors of arthropod saliva and the potential for these factors to serve as vaccine targets to prevent pathogen transmission

In general, attempts to develop vaccines for pathogens transmitted by arthropods have met with little or no success. It has been widely observed that the saliva of arthropods that transmit disease enhances the infectivity of pathogens the arthropod transmits to the vertebrate host. Indeed, it has been observed that vaccinating against components of the saliva of arthropods or against antigens expressed in the gut of arthropods can protect the host from infection and decrease the viability of the arthropod. These results suggest that multi-subunit vaccines that target the pathogen itself as well as arthropod salivary gland components and arthropod gut antigens may be the most effective at controlling arthropod-borne pathogens as these vaccines would target several facets of the lifecycle of the pathogen. This review covers known immunomodulators in arthropod salivary glands, instances when arthropod saliva has been shown to enhance infection and a limited number of examples of antiarthropod vaccines, with emphasis on three arthropods: sandflies, mosquitoes and hard ticks.

The productivity effects of cattle tick (Boophilus microplus) infestation on cattle, with particular reference to Bos indicus cattle and their crosses

In response to uncertainty among cattle producers in Australia regarding the need to treat Bos indicus and B. indicus crossbreeds, the scientific literature relating to the productivity effects of Boophilus microplus on cattle of all breeds was reviewed. Estimates of the mean effect of each engorging tick (damage coefficient, d) were made from a simple analysis of the reported data. On average, each engorging female tick is responsible for the loss of 1.37 +/- 0.25 g bodyweight in B. taurus cattle. The comparable value for B. taurusxB. indicus cattle is 1.18 +/- 0.21 g/engorging tick. These values were not statistically significantly different, indicating that if a threshold approach to tick control were taken, then the threshold number of standard ticks would be the same regardless of cattle genotype. No studies provided useable estimates of the effect of tick infestation on pure B. indicus cattle. An economic threshold for treatment, below which acaricide application is not beneficial, can be predicted, using known values for the cost of acaricide application and the price of beef. However, the application of a threshold approach to control has not been embraced by government advisers and runs contrary to the accepted principals of strategic control programs.

Haematophagous arthropod saliva and host defense system: a tale of tear and blood

The saliva from blood-feeding arthropod vectors is enriched with molecules that display diverse functions that mediate a successful blood meal. They function not only as weapons against host's haemostatic, inflammatory and immune responses but also as important tools to pathogen establishment. Parasites, virus and bacteria taking advantage of vectors' armament have adapted to facilitate their entry in the host. Today, many salivary molecules have been identified and characterized as new targets to the development of future vaccines. Here we focus on current information on vector's saliva and the molecules responsible to modify host's hemostasis and immune response, also regarding their role in disease transmission.

Tick saliva inhibits differentiation, maturation and function of murine bone-marrow-derived dendritic cells

Haematophagous arthropod vectors such as mosquitoes, tsetse flies, sandflies and ticks have evolved salivary immunomodulatory factors that prevent the vertebrate host from rejecting them meanwhile enhancing pathogen transmission. As dendritic cells (DC) play a major role in host immune responses, we studied the effects of Rhipicephalus sanguineus tick saliva on DC differentiation and maturation. Flow cytometry analysis revealed that the addition of saliva to bone marrow cells inhibits the differentiation of DC and decreased the population of differentiated immature DC, increasing the levels of major histocompatibility complex (MHC) class II while not altering the expression of costimulatory (CD40, CD80 and CD86) and adhesion (CD54) molecules. Furthermore, maturation of DC stimulated by lipopolysaccharide (LPS) in the presence of saliva resulted in a lower expression of costimulatory molecules, but did not alter the up-regulation of MHC class II and CD54. The lipopolysaccharide (LPS)-matured DC cultured with saliva also presented reduced production of interleukin-12, whereas interleukin-10 production was unaltered. Assessment of the function of DC cultured with tick saliva revealed them to be poor stimulators of cytokine production by antigen-specific T cells. Our data indicate a novel modulatory role for the saliva of arthropod vectors at an initial step of the immune response through the inhibition of differentiation and maturation of DC into functional antigen-presenting cells.

Susceptibility of mice (Mus musculus) to repeated infestation with Amblyomma americanum (Acari: Ixodidae) ticks

Laboratory mice, Mus musculus (L.), BALB/c strain, were assessed for their ability to develop resistance to repeated infestation by Amblyomma americanum (L.) ticks. Mice were infested five consecutive times with A. americanum nymphs. No decrease in tick viability was seen after five infestations, suggesting that BALB/c mice do not develop immune-mediated resistance to A. americanum. In contrast, tick viability was significantly reduced in the second infestation of a New Zealand White rabbit, a laboratory animal known to develop resistance to A. americanum.