The tick salivary protein Salp15 inhibits the killing of serum-sensitive Borrelia burgdorferi sensu lato isolates

Suppressive effects of neutrophil by Salp16-like salivary gland proteins from Ixodes persulcatus Schulze tick

Salp16, a 16-kDa tick salivary gland protein, is known to be the molecule involved in the transmission of Anaplasma phagocytophilum, an obligate intracellular pathogen causing zoonotic anaplasmosis, from its mammalian hosts to Ixodes scapularis. Recently, the presence of A. phagocytophilum was documented in Japan and Ixodes persulcatus was identified as one of its vectors. The purpose of this study was to identify Salp16 genes in I. persulcatus and characterize their function. Two cDNA clones encoding the Salp16-like sequences were obtained from the salivary glands of fed female I. persulcatus ticks and designated Salp16 Iper1 and Iper2. Gene expression analyses showed that the Salp16 Iper genes were expressed specifically in the salivary glands and were up-regulated by blood feeding. These proteins attenuated the oxidative burst of activated bovine neutrophils and inhibited their migration induced by the chemoattractant interleukin-8 (IL-8). These results demonstrate that Salp16 Iper proteins contribute to the establishment of blood feeding as an immunosuppressant of neutrophil, an essential factor in innate host immunity. Further examination of the role of Salp16 Iper in the transmission of pathogens, including A. phagocytophilum, will increase our understanding of the tick-host-pathogen interface.

Innate immunity networks during infection with Borrelia burgdorferi

The recognition of Borrelia species represents a complex process in which multiple components of the immune system are involved. In this review, we summarize the interplay between the host innate system and Borrelia spp., from the recognition by pattern recognition receptors (PRRs) to the induction of a complex network of proinflammatory mediators. Several PRR families are crucial for recognition of Borrelia spp., including Toll-like receptors (TLRs) and Nucleotide Oligomerization Domain (NOD)-like receptors (NLRs). TLR-2 is crucial for the recognition of outer surface protein (Osp)A from Borrelia spp. and together with TLR8 mediates phagocytosis of the microorganism and production of type I interferons. Intracellular receptors such as TLR7, TLR8 and TLR9 on the one hand and the NLR receptor NOD2 on the other hand, represent the second major recognition system of Borrelia. PRR-dependent signals induce the release of pro-inflammatory cytokines such as interleukin-1 and T-helper-derived cytokines, which are thought to mediate the inflammation during Lyme disease. Understanding the regulation of host defense mechanisms against Borrelia has the potential to lead to the discovery of novel immunotherapeutic targets to improve the therapy against Lyme disease.

Genetic diversity of Salp15 in the Ixodes ricinus complex (Acari: Ixodidae)

Salp15, a 15-kDa tick salivary gland protein, is both essential for ticks to successfully obtain host blood and also facilitates transmission of Lyme borreliosis. To determine whether the Salp15 gene is expressed in Ixodes persulcatus and Ixodes sinensis, principle vectors of Lyme borreliosis in China, we studied transcriptions of this gene in semi-engorged larvae, nymph and adults of these two species. A total of eight Salp15 homologues, five in I. persulcatus and three in I. sinensis, were identified by reverse transcriptase–polymerase chain reaction (RT-PCR). Interestingly, the intra-species similarity of Salp15 is approximately equal to its interspecies similarity and more than one Salp15 protein is expressed in a certain tick developmental stage. Comparison of DNA and proteins with other available tick Salp15 homologues suggests that the Salp15 superfamily is genetically conserved and diverse in the Ixodes ricinus complex. These findings indicate that Salp15 proteins in the I. ricinus complex may play an essential role in interacting with the host immune system and transmission of Borrelia genospecies.

Coinfection of tick cell lines has variable effects on replication of intracellular bacterial and viral pathogens

Ticks transmit various human and animal microbial pathogens and may harbour more than one pathogen simultaneously. Both viruses and bacteria can trigger, and may subsequently suppress, vertebrate host and arthropod vector anti-microbial responses. Microbial coinfection of ticks could lead to an advantage or disadvantage for one or more of the microorganisms. In this preliminary study, cell lines derived from the ticks Ixodes scapularis and Ixodes ricinus were infected sequentially with 2 arthropod-borne pathogens, Borrelia burgdorferi s.s., Ehrlichia ruminantium, or Semliki Forest virus (SFV), and the effect of coinfection on the replication of these pathogens was measured. Prior infection of tick cell cultures with the spirochaete B. burgdorferi enhanced subsequent replication of the rickettsial pathogen E. ruminantium whereas addition of spirochaetes to cells infected with E. ruminantium had no effect on growth of the latter. Both prior and subsequent presence of B. burgdorferi also had a positive effect on SFV replication. Presence of E. ruminantium or SFV had no measurable effect on B. burgdorferi growth. In tick cells infected first with E. ruminantium and then with SFV, virus replication was significantly higher across all time points measured (24, 48, 72h post infection), while presence of the virus had no detectable effect on bacterial growth. When cells were infected first with SFV and then with E. ruminantium, there was no effect on replication of either pathogen. The results of this preliminary study indicate that interplay does occur between different pathogens during infection of tick cells. Further study is needed to determine if this results from direct pathogen-pathogen interaction or from effects on host cell defences, and to determine if these observations also apply in vivo in ticks. If presence of one pathogen in the tick vector results in increased replication of another, this could have implications for disease transmission and incidence.

Pyruvate protects pathogenic spirochetes from H2O2 killing

Pathogenic spirochetes cause clinically relevant diseases in humans and animals, such as Lyme disease and leptospirosis. The causative agent of Lyme disease, Borrelia burgdorferi, and the causative agent of leptospirosis, Leptospria interrogans, encounter reactive oxygen species (ROS) during their enzootic cycles. This report demonstrated that physiologically relevant concentrations of pyruvate, a potent H2O2 scavenger, and provided passive protection to B. burgdorferi and L. interrogans against H2O2. When extracellular pyruvate was absent, both spirochetes were sensitive to a low dose of H2O2 (≈0.6 µM per h) generated by glucose oxidase (GOX). Despite encoding a functional catalase, L. interrogans was more sensitive than B. burgdorferi to H2O2 generated by GOX, which may be due to the inherent resistance of B. burgdorferi because of the virtual absence of intracellular iron. In B. burgdorferi, the nucleotide excision repair (NER) and the DNA mismatch repair (MMR) pathways were important for survival during H2O2 challenge since deletion of the uvrB or the mutS genes enhanced its sensitivity to H2O2 killing; however, the presence of pyruvate fully protected ΔuvrB and ΔmutS from H2O2 killing further demonstrating the importance of pyruvate in protection. These findings demonstrated that pyruvate, in addition to its classical role in central carbon metabolism, serves as an important H2O2 scavenger for pathogenic spirochetes. Furthermore, pyruvate reduced ROS generated by human neutrophils in response to the Toll-like receptor 2 (TLR2) agonist zymosan. In addition, pyruvate reduced neutrophil-derived ROS in response to B. burgdorferi, which also activates host expression through TLR2 signaling. Thus, pathogenic spirochetes may exploit the metabolite pyruvate, present in blood and tissues, to survive H2O2 generated by the host antibacterial response generated during infection.

A Nod to disease vectors: mitigation of pathogen sensing by arthropod saliva

Arthropod saliva possesses anti-hemostatic, anesthetic, and anti-inflammatory properties that facilitate feeding and, inadvertently, dissemination of pathogens. Vector-borne diseases caused by these pathogens affect millions of people each year. Many studies address the impact of arthropod salivary proteins on various immunological components. However, whether and how arthropod saliva counters Nod-like (NLR) sensing remains elusive. NLRs are innate immune pattern recognition molecules involved in detecting microbial molecules and danger signals. Nod1/2 signaling results in activation of the nuclear factor-κB and the mitogen-activated protein kinase pathways. Caspase-1 NLRs regulate the inflammasome~– a protein scaffold that governs the maturation of interleukin (IL)-1β and IL-18. Recently, several vector-borne pathogens have been shown to induce NLR activation in immune cells. Here, we provide a brief overview of NLR signaling and discuss clinically relevant vector-borne pathogens recognized by NLR pathways. We also elaborate on possible anti-inflammatory effects of arthropod saliva on NLR signaling and microbial pathogenesis for the purpose of exchanging research perspectives.

Tick vaccines and the control of tick-borne pathogens

Ticks are obligate hematophagous ectoparasites that transmit a wide variety of pathogens to humans and animals. The incidence of tick-borne diseases has increased worldwide in both humans and domestic animals over the past years resulting in greater interest in the study of tick-host-pathogen interactions. Advances in vector and pathogen genomics and proteomics have moved forward our knowledge of the vector-pathogen interactions that take place during the colonization and transmission of arthropod-borne microbes. Tick-borne pathogens adapt from the vector to the mammalian host by differential gene expression thus modulating host processes. In recent years, studies have shown that targeting tick proteins by vaccination can not only reduce tick feeding and reproduction, but also the infection and transmission of pathogens from the tick to the vertebrate host. In this article, we review the tick-protective antigens that have been identified for the formulation of tick vaccines and the effect of these vaccines on the control of tick-borne pathogens.

Novel immunomodulators from hard ticks selectively reprogramme human dendritic cell responses

Hard ticks subvert the immune responses of their vertebrate hosts in order to feed for much longer periods than other blood-feeding ectoparasites; this may be one reason why they transmit perhaps the greatest diversity of pathogens of any arthropod vector. Tick-induced immunomodulation is mediated by salivary components, some of which neutralise elements of innate immunity or inhibit the development of adaptive immunity. As dendritic cells (DC) trigger and help to regulate adaptive immunity, they are an ideal target for immunomodulation. However, previously described immunoactive components of tick saliva are either highly promiscuous in their cellular and molecular targets or have limited effects on DC. Here we address the question of whether the largest and globally most important group of ticks (the ixodid metastriates) produce salivary molecules that specifically modulate DC activity. We used chromatography to isolate a salivary gland protein (Japanin) from Rhipicephalus appendiculatus ticks. Japanin was cloned, and recombinant protein was produced in a baculoviral expression system. We found that Japanin specifically reprogrammes DC responses to a wide variety of stimuli in vitro, radically altering their expression of co-stimulatory and co-inhibitory transmembrane molecules (measured by flow cytometry) and their secretion of pro-inflammatory, anti-inflammatory and T cell polarising cytokines (assessed by Luminex multiplex assays); it also inhibits the differentiation of DC from monocytes. Sequence alignments and enzymatic deglycosylation revealed Japanin to be a 17.7 kDa, N-glycosylated lipocalin. Using molecular cloning and database searches, we have identified a group of homologous proteins in R. appendiculatus and related species, three of which we have expressed and shown to possess DC-modulatory activity. All data were obtained using DC generated from at least four human blood donors, with rigorous statistical analysis. Our results suggest a previously unknown mechanism for parasite-induced subversion of adaptive immunity, one which may also facilitate pathogen transmission.

Dendritic cells (DC) are specialised cells of the vertebrate immune system. DC can sense different types of infectious agents and parasites, and both trigger and help regulate the specific types of immunity needed to eliminate them. We have discovered that the largest and globally most important group of hard ticks produce a unique family of proteins in their saliva that selectively targets DC, radically altering functions that would otherwise induce robust immune responses; these proteins also prevent DC developing from precursor cells. The production of these salivary molecules may help to explain two highly unusual features of these hard ticks compared with other blood-feeding parasites: their ability to feed continuously on their vertebrate hosts for considerable lengths of time (7 days or more) without eliciting potentially damaging immune responses, and their capacity to transmit possibly the greatest variety of pathogens of any type of invertebrate.

Review of evidence for immune evasion and persistent infection in Lyme disease

Is chronic illness in patients with Lyme disease caused by persistent infection? Three decades of basic and clinical research have yet to produce a definitive answer to this question. This review describes known and suspected mechanisms by which spirochetes of the Borrelia genus evade host immune defenses and survive antibiotic challenge. Accumulating evidence indicates that Lyme disease spirochetes are adapted to persist in immune competent hosts, and that they are able to remain infective despite aggressive antibiotic challenge. Advancing understanding of the survival mechanisms of the Lyme disease spirochete carry noteworthy implications for ongoing research and clinical practice.

Vaccination against Lyme disease: past, present, and future

Lyme borreliosis is a zoonotic disease caused by Borrelia burgdorferi sensu lato bacteria transmitted to humans and domestic animals by the bite of an Ixodes spp. tick (deer tick). Despite improvements in diagnostic tests and public awareness of Lyme disease, the reported cases have increased over the past decade to approximately 30,000 per year. Limitations and failed public acceptance of a human vaccine, comprised of the outer surface A (OspA) lipoprotein of B. burgdorferi, led to its demise, yet current research has opened doors to new strategies for protection against Lyme disease. In this review we discuss the enzootic cycle of B. burgdorferi, and the unique opportunities it poses to block infection or transmission at different levels. We present the correlates of protection for this infectious disease, the pros and cons of past vaccination strategies, and new paradigms for future vaccine design that would include elements of both the vector and the pathogen.

Complement evasion by Borrelia burgdorferi: it takes three to tango

The complement system is one of the major innate defense mechanisms Borrelia burgdorferi sensu lato has to overcome to establish an infection of mammalian hosts and to cause Lyme borreliosis in humans. Borrelia prevents complement-mediated killing during host colonization through (i) recruitment of host complement regulators by Borrelia, (ii) evasion mechanisms by Borrelia itself, and (iii) exploitation of tick proteins by Borrelia. These interactions with complement can be host species-specific. This review provides an overview of interactions between Borrelia, tick, and host leading to evasion of complement-mediated killing.

A tick mannose-binding lectin inhibitor interferes with the vertebrate complement cascade to enhance transmission of the lyme disease agent

The Lyme disease agent Borrelia burgdorferi is primarily transmitted to vertebrates by Ixodes ticks. The classical and alternative complement pathways are important in Borrelia eradication by the vertebrate host. We recently identified a tick salivary protein, designated P8, which reduced complement-mediated killing of Borrelia. We now discover that P8 interferes with the human lectin complement cascade, resulting in impaired neutrophil phagocytosis and chemotaxis and diminished Borrelia lysis. Therefore, P8 was renamed the tick salivary lectin pathway inhibitor (TSLPI). TSLPI-silenced ticks, or ticks exposed to TSLPI-immune mice, were hampered in Borrelia transmission. Moreover, Borrelia acquisition and persistence in tick midguts was impaired in ticks feeding on TSLPI-immunized, B. burgdorferi-infected mice. Together, our findings suggest an essential role for the lectin complement cascade in Borrelia eradication and demonstrate how a vector-borne pathogen co-opts a vector protein to facilitate early mammalian infection and vector colonization.

Distinctive amino acid composition profiles in salivary proteins of the tick Ixodes scapularis

Bioinformatic analysis of the amino acid composition of proteins of the tick Ixodes scapularis showed that, in comparison to other secreted proteins, salivary proteins in general have higher frequencies of polar residues and lower frequencies of the non-polar residues leucine and valine. Computer prediction of linear B-cell epitopes showed that polar residues were associated with the presence of high-quality epitopes and that tick salivary proteins included significantly more proteins with predicted high-quality epitopes than did other secreted proteins. The results provided no evidence that salivary proteins as a whole have evolved characteristics minimizing their antigenicity to the vertebrate host. Certain salivary proteins may indeed have evolved low antigenicity, but the I. scapularis sialome include at least some apparently antigenic proteins that might be tested experimentally to determine whether they would be suitable candidates for anti-tick vaccines.

Lyme disease: Part I. Advances and perspectives

Lyme disease (LD) is an increasingly recognized multisystem, insect-borne zoonosis. Prevalent worldwide, it has a variety of presentations at different stages of infection. The characteristic rash with central clearing known as erythema chronicum migrans, or simply erythema migrans, appears in its first stage. Typical features may be absent, and important variations are evident among cases seen in different parts of the world. LD may be difficult to diagnose clinically; knowledge about its epidemiology and transmission may be of assistance when the diagnosis is unclear. Based upon our experience with LD and a comprehensive literature review, we provide an update of LD epidemiology, pathophysiology, and management. We also cover the three clinical stages of LD that parallel those of syphilis, another spirochetal disease.

Neuroborreliosis: pathogenesis, symptoms, diagnosis and treatment

Lyme disease is the most common human tick-borne disease in the northern hemisphere. This article describes the current knowledge of several aspects of Lyme neuroborreliosis. The epidemiology is reviewed first, with special respect to the difference between European and American disease. Then, the current knowledge about the pathogenesis of Lyme neuroborreliosis is presented, with emphasis on immune evasion strategies. Furthermore, the clinical picture of acute Lyme neuroborreliosis and the frequently discussed post-Lyme disease syndrome are critically discussed. The commonly used diagnostic strategies, as well as the relevance of the lymphocyte transformation test, CD57+/CD3- cell count and CXCL13, are presented. Finally, the therapeutic options are described to give a balanced overview of all aspects of this disease.

Lyme borreliosis in dogs and cats: background, diagnosis, treatment and prevention of infections with Borrelia burgdorferi sensu stricto

Lyme borreliosis (LB), synonymous with the often-used term Lyme disease, is an infectious disease caused by the spirochetal bacterium Borrelia burgdorferi. LB is the most frequent vector-borne disease in humans in the Northern Hemisphere. In animals, clinically apparent disease is found primarily in dogs. Severe polyarthritis, fever and lameness in dogs are reported from the main endemic areas of North America: the New England States, and eastern parts of the United States; several cases of LB are also seen in California and the Midwest. Because of the difficulties in finding sufficient indicative clinical signs, additional information (detailed case history, laboratory testing for antibodies) is especially important to make the clinical diagnosis of Lyme borreliosis. This article reviews the etiology, diagnosis, therapy, and prevention of LB.

Identification and characterization of Ixodes scapularis antigens that elicit tick immunity using yeast surface display

Repeated exposure of rabbits and other animals to ticks results in acquired resistance or immunity to subsequent tick bites and is partially elicited by antibodies directed against tick antigens. In this study we demonstrate the utility of a yeast surface display approach to identify tick salivary antigens that react with tick-immune serum. We constructed an Ixodes scapularis nymphal salivary gland yeast surface display library and screened the library with nymph-immune rabbit sera and identified five salivary antigens. Four of these proteins, designated P8, P19, P23 and P32, had a predicted signal sequence. We generated recombinant (r) P8, P19 and P23 in a Drosophila expression system for functional and immunization studies. rP8 showed anti-complement activity and rP23 demonstrated anti-coagulant activity. Ixodes scapularis feeding was significantly impaired when nymphs were fed on rabbits immunized with a cocktail of rP8, rP19 and rP23, a hall mark of tick-immunity. These studies also suggest that these antigens may serve as potential vaccine candidates to thwart tick feeding.

Infectivity of Borrelia burgdorferi sensu lato is unaltered in C3-deficient mice

B. burgdorferi, B. afzelii, and B. bavariensis show resistance to mouse and human complement. B. garinii and B. valaisiana are sensitive to mouse and human complement. We evaluated whether the absence of C3 in mice influenced infectivity and pathogenicity of different Borrelia species. C3 knockout mice (C3-/-) and syngeneic C57Bl/6 wild-type (WT) mice were challenged with 5 different Borrelia species. After 2 weeks, quantitative PCR (qPCR), culture, histopathology, and immunofluorescence were performed on heart, joint, brain, bladder, and skin. Spirochaetes were detected by qPCR after infection with B. burgdorferi, B. afzelii, or B. bavariensis strains. In joints of C3-/-, but not WT mice challenged with B. burgdorferi, spirochaetes were detected by qPCR. No other significant differences between C3-/- and WT mice were seen. Histopathology demonstrated concordance between borrelia load and inflammation score. Only after B. burgdorferi and B. afzelii infection, spirochaetes were detected by immunofluorescence microscopy. B. burgdorferi was cultured from heart, joint, bladder, and skin from all mice within 2 weeks. B. afzelii and B. bavariensis grew only from heart tissue from both C3-/- and WT mice after 2-6 weeks. The infectivity and pathogenicity of complement-resistant Borrelia strains is unchanged in complement-deficient mice. Complement-susceptible strains do not become infectious in the absence of C3.

Infectious arthritis and immune dysregulation: lessons from Lyme disease

PURPOSE OF REVIEW

Borrelia burgdorferi colonization of the joints induces an inflammatory response, which in some individuals progresses to chronic arthritis. In this review, we discuss novel pathways that are implicated in disease development by modulating host defenses to B. burgdorferi infection.

RECENT FINDINGS

The use of transgenic mice and gene expression analyses has revealed novel pathways involved in pathogenesis of Lyme disease. It is now clear that B. burgdorferi exploits an array of salivary gland proteins of the tick to evade immune responses in the mammalian host. The spirochete also modulates its surface protein profile upon infection and induces anti-inflammatory cytokines, favoring survival of the pathogen. The host defense involves toll-like receptors (TLRs), such as TLR2 and others, in B. burgdorferi recognition. To further dissect the genetic predisposition to treatment-refractory Lyme arthritis, HLA-DR transgenic mice have been used.

SUMMARY

The cause and pathogenesis of Lyme arthritis are complex. Elucidating the mechanisms that govern this chronic inflammatory response will provide direct insights into other infectious arthritides and the development of novel therapeutic approaches against B. burgdorferi infection.

Lyme borreliosis vaccination: the facts, the challenge, the future

Lyme disease, or Lyme borreliosis, the most prevalent arthropod-borne disease in the Western world, is caused by spirochetes belonging to the Borrelia burgdorferi sensu lato group and is predominantly transmitted through Ixodes ticks. There is currently no vaccine available to prevent Lyme borreliosis in humans. Borrelia outer membrane proteins are reviewed which have been investigated as vaccine candidates. In addition, several tick proteins are discussed, on which anti-tick vaccines have been based, or are interesting future candidates, to prevent transmission of the spirochete from the tick vector to the mammalian host. Finally, novel vaccination strategies to prevent Lyme borreliosis are proposed, based on multiple Borrelia antigens, tick antigens or a combination of both Borrelia as well as tick antigens.

Two novel Salp15-like immunosuppressant genes from salivary glands of Ixodes persulcatus Schulze tick

Salp15, a 15-kDa tick salivary gland protein, is known for several suppressive activities against host immunity and critical functions for the transmission of Lyme borrelia in Ixodes scapularis and Ixodes ricinus, the major vectors found in North America and Western Europe. Salp15 inhibits the activation of cluster of differentiation (CD)4(+)T-cells through the repression of T-cell receptor (TCR)-triggered calcium fluxes and interleukin (IL)-2 production. Furthermore, Salp15 adheres to the spirochaeta and specifically interacts with its outer surface protein C. The binding of Salp15 to Borrelia burgdorferi protects it from antibody-mediated killing in vitro. The aim of this study is to identify the Salp15 genes in Ixodes persulcatus Schulze, the specific vector for human Lyme borreliosis in Japan. Two cDNA clones encoding the Salp15-like sequence were obtained from salivary glands of fed female ticks. These genes encode 135- and 132-amino acid proteins, designated Salp15 Iper-1 and Salp15 Iper-2, respectively, both having signal peptide sequences and predicted to be secretory proteins. Salp15 Iper-1 and -2 showed 51.8 and 68.2% similarity to I. scapularis Salp15, respectively. Reverse transcriptase PCR analysis showed that Salp15 Iper genes were expressed specifically in the salivary glands throughout life cycle stages of the ticks and were up-regulated by blood feeding. In the I. persulcatus-derived sequences, the C-terminal part, which is the binding domain to the CD4 molecule of T-cells in I. scapularis Salp15, was well conserved. In the future, it will be necessary to analyse immunosuppressive functions of I. persulcatus Salp15 and their interaction with Borrelia spp. in Japan.

Identification and functional characterisation of Complement Regulator Acquiring Surface Protein-1 of serum resistant Borrelia garinii OspA serotype 4

Background

B. burgdorferi sensu lato (sl) is the etiological agent of Lyme borreliosis in humans. Spirochetes have adapted themselves to the human immune system in many distinct ways. One important immune escape mechanism for evading complement activation is the binding of complement regulators Factor H (CFH) or Factor H-like protein1 (FHL-1) to Complement Regulator-Acquiring Surface Proteins (CRASPs).

Results

We demonstrate that B. garinii OspA serotype 4 (ST4) PBi resist complement-mediated killing by binding of FHL-1. To identify the primary ligands of FHL-1 four CspA orthologs from B. garinii ST4 PBi were cloned and tested for binding to human CFH and FHL-1. Orthologs BGA66 and BGA71 were found to be able to bind both complement regulators but with different intensities. In addition, all CspA orthologs were tested for binding to mammalian and avian CFH. Distinct orthologs were able to bind to CFH of different animal origins.

Conclusions

B. garinii ST4 PBi is able to evade complement killing and it can bind FHL-1 to membrane expressed proteins. Recombinant proteins BGA66 can bind FHL-1 and human CFH, while BGA71 can bind only FHL-1. All recombinant CspA orthologs from B. garinii ST4 PBi can bind CFH from different animal origins. This partly explains the wide variety of animals that can be infected by B. garinii.

Molecular identification of Salp15, a key salivary gland protein in the transmission of lyme disease spirochetes, from Ixodes persulcatus and Ixodes pacificus (Acari: Ixodidae)

Salp15 is a multifunctional protein, vital to the tick in its need to obtain vertebrate host blood without stimulating a host inflammatory and immune response. The Salpl5 protein from both Ixodes scapularis Say and Ixodes ricinus (L.), the principal vectors of the Lyme disease spirochete in eastern North America and Europe, respectively, have been well characterized and found to bind the murine CD4 receptor, DC-SIGN, and the OspC protein of Borrelia burgdorferi. In the current study, we characterized the full salp15 gene in Ixodes pacificus Cooley & Kohls and Ixodes persulcatus Schulze, the principal vectors of Lyme disease spirochetes in western North America and Asia, respectively. In comparing the Salp15 protein of all four principal vector ticks of public health importance for the transmission of Lyme disease spirochetes, we find the 53 C-terminal amino acids to have a high degree of similarity. There are at least three clades in the tree of Salp15 and its homologues, probably representing a multigene family.

Inhibition of neutrophil function by two tick salivary proteins

The saliva of hematophagous arthropods contains potent anti-inflammatory and antihemostatic activities that promote acquisition of the blood meal and enhance infection with pathogens. We have shown that polymorphonuclear leukocytes (PMN) treated with the saliva of the tick Ixodes scapularis have reduced expression of beta(2) integrins, impaired PMN adherence, and reduced killing of Borrelia burgdorferi, the causative agent of Lyme disease. Here we describe two Ixodes proteins that are induced upon tick feeding and expressed predominantly in the salivary glands. Using saliva harvested from ticks with reduced levels of ISL 929 and ISL 1373 through targeted RNA interference knockdown, as well as purified recombinant proteins, we show the effects of these proteins on downregulation of PMN integrins and inhibition of the production of O(2)(-) by PMN in vitro. Mice immunized with ISL 929/1373 had increased numbers of PMN at the site of tick attachment and a lower spirochete burden in the skin and joints 21 days after infection compared to control-immunized animals. Our results suggest that ISL 929 and ISL 1373 contribute to the inhibition of PMN functions shown previously with tick saliva and support important roles for these inhibitory proteins in the modulation of PMN function in vivo.

Positive selection in tick saliva proteins of the Salp15 family

When taking their blood meal on the mammalian host, ticks transfer a multitude of different proteins from their saliva into the host. Some of these proteins are hijacked by pathogens for their own purposes. Borrelia burgdorferi, the Lyme disease agent, is critically dependent on the presence of the tick protein Salp15 when infecting the host. Similarly, Anaplasma phagocytophilum, which causes anaplasmosis, needs Salp16, a homologue of Salp15, to get transferred from the host into the tick. Here we analyzed whether adaptive evolution has shaped the Salp15 protein family. Using site-specific estimates of K(A)/K(S) ratios, we identified different positions within the Salp15 protein family which have undergone a phase of positive selection. Additionally, we analyzed the B. burgdorferi protein interacting with Salp15, OspC. Again, sites showing signs of positive selection were identified, although they are more likely a result of the antigenic features of OspC than of the influence of Salp15. The identification of probably functionally relevant sites in the Salp15 family might direct the detailed experimental analysis of their interaction with human and bacterial proteins.

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.