Advertisement
  • Loading metrics

Salivating for Knowledge: Potential Pharmacological Agents in Tick Saliva

Salivating for Knowledge: Potential Pharmacological Agents in Tick Saliva

  • Joppe W. R Hovius, 
  • Marcel Levi, 
  • Erol Fikrig
PLOS
x

The incidence of tick-borne diseases has drastically increased over the past few years [1,2], resulting in a marked increase in research on tick–host–pathogen interactions. As a result, the knowledge on molecules present in tick saliva and their function has significantly expanded [3,4]. Ticks are obligate hematophagous ectoparasites, and hundreds of tick species are distributed worldwide. While taking a blood meal, ticks are attached to their host for several days and introduce saliva into the host skin. Like saliva from other hematophagous animals, such as mosquitoes, flies, leeches, and nematode species, tick saliva contains a wide range of physiologically active molecules that are crucial for attachment to the host or for the transmission of pathogens [5], and that interact with host processes, including coagulation and fibrinolysis, immunity and inflammation, and angiogenesis [3,6,7]. In this article, we discuss molecules in tick saliva that have been intensively studied in vitro or in animal models for human diseases, and that, due to their specificity, are potential future anticoagulant or immunosuppressive agents. We also discuss how immunologically targeting specific tick salivary proteins could prevent the transmission of tick-borne pathogens from the tick to the host.

Anticoagulants

The hemostatic response enables mammals to control blood loss during vascular injury. Platelets adhere to macromolecules in exposed subendothelial tissue and aggregate to form a hemostatic plug, while local activation of plasma coagulation factors leads to generation of a fibrin clot that reinforces the platelet aggregate. The coagulation cascade starts when exposed subendothelial tissue factor (TF) binds to activated factor VII (FVIIa). This complex activates factor X (forming FXa), which mediates the formation of minute amounts of thrombin that activate other coagulation proteases and additional platelets. Subsequently, by means of two amplification loops (Figure 1), more thrombin is generated, which leads to fibrinogen-to-fibrin conversion and fibrin deposition [8].

thumbnail
Figure 1. Schematic Overview of the Coagulation Cascade

The two major amplification loops in the coagulation cascade are depicted. The first amplification loop consists of TF-FVIIa-mediated factor IX (FIX) activation, which leads to the generation of more FXa. A second amplification loop is formed by the activation of factor XI (FXIa) by thrombin, which results in more activated FIX (FIXa), and, subsequently, additional FXa generation. The right panel indicates how selected tick proteins exert their anticoagulant effect.

FIIa, activated factor II; FVa, activated factor V; FVIIIa, activated factor VIII.

https://doi.org/10.1371/journal.pmed.0050043.g001

Tick feeding is hampered by the hemostatic response of the host. Therefore tick saliva contains an extensive selection of molecules that counteract coagulation, enhance fibrinolysis, and inhibit platelet aggregation [7]. Traditional anticoagulant agents such as unfractionated heparin and vitamin K antagonists (e.g., warfarin) have a narrow therapeutic index, requiring frequent monitoring and dose adjustments [7]. Tick saliva presents a possible source of novel, and ideally more easily used, anticoagulant agents (Figure 1) [7].

Five Key Papers in the Field

Hepburn et al., 2007 [40] After identification of a specific activated C5 inhibitor, OMCI, the authors showed how this protein can be used in an experimental animal model for myasthenia gravis.

Paveglio et al., 2007 [50] Showed that a T cell inhibitor from tick saliva, Salp15, is able to prevent the development of pathological features in an animal model for atopic asthma.

Labuda et al., 2006 [55] Showed that an anti-tick vaccine, directed against the 64TRP cement protein in tick saliva, prevented lethal infection of mice with the tick-borne encephalitis virus, indicating that anti-tick vaccines could be used to combat tick-borne pathogens.

Ramamoorthi et al., 2005 [5] Showed that B. burgdorferi, the causative agent of Lyme disease, uses a protein in tick saliva, Salp15, to establish an infection in the mammalian host, underscoring the complex tick–host–pathogen interactions that are involved in the development of Lyme disease.

Waxman et al., 1990 [9] Identified the first highly specific activated factor X inhibitor in tick saliva, TAP. This research has been the inspiration for numerous researchers working in the field of coagulation.

Factor Xa inhibitors.

Saliva from the soft tick Ornithodoros moubata contains a serine protease inhibitor of FXa—tick anticoagulant peptide (TAP). TAP is a tight-binding specific FXa inhibitor that inhibits clotting of human plasma ex vivo [9]. The inhibitory characteristics and the high selectivity of recombinant forms of TAP (rTAP) for FXa are due to the interaction of rTAP with the active site as well as with regions remote from the active site pocket of FXa [10]. rTAP has been tested in a variety of animal models for both venous and arterial thrombosis [11–13]. A recent study showed that rTAP, when fused to a single-chain antibody specifically targeting activated platelets (through binding to the platelet receptor GPIIb/IIIa), had highly effective antithrombotic properties in comparison to enoxaparin in a murine carotid artery thrombosis model. In addition, in contrast to conventional anticoagulants tested, the TAP–antibody fusion protein did not prolong bleeding time [14]. Future research should reveal whether this or similar approaches are equally effective and safe in humans. Other FXa inhibitors characterized in tick saliva are shown in Table 1 [15,16].

Tissue factor pathway inhibitors.

In view of the central role of TF in the initiation of coagulation in both physiological and pathological states, targeting TF may be an effective antithrombotic strategy. Tick saliva contains several TF pathway inhibitors (TFPIs) (Table 1) [7,17]. Recently, Ixolaris was identified in saliva from the deer tick Ixodes scapularis [17]. Ixolaris has two kunitz-like domains, a type of domain conserved in a wide family of serine protease inhibitors, and sequence homology to human TFPI [18]. In a rat model for venous thrombosis, administration of recombinant Ixolaris resulted in effective antithrombotic activity, without hemorrhage or bleeding [19]. Because of its fast and tight binding to FXa, giving rapid-acting, selective, and long-lasting effects, and the encouraging results in vivo, Ixolaris could serve as a template for potential new anticoagulant agents targeting the TF pathway.

Direct thrombin inhibitors.

In comparison with heparin (derivatives), which act via antithrombin, direct thrombin inhibitors more effectively inhibit clot-bound thrombin, which is likely to result in a stronger antithrombotic effect [20]. Several specific direct thrombin inhibitors have been characterized in tick saliva (Table 1) [7,21–24], but most have not yet been tested in vivo. Recently a new direct thrombin inhibitor, variegin [25], was characterized from the tropical bont tick, Amblyomma variegatum, and shown to be structurally similar to, but much more potent than, hirulog, a 20-amino-acid synthetic thrombin inhibitor based on the natural leech peptide hirudin. Hirulog belongs to a class of drugs that have been approved for treatment of patients with acute coronary syndromes who are undergoing percutaneous coronary intervention [26].

Immunosuppressors

Cellular innate immune responses, depending on invariant receptors such as the Toll-like receptors, are one of the first lines of defence against invading microbes. Another important innate defence system is the complement cascade. Activation of the complement system leads to opsonization of an invading pathogen as well as formation of the membrane attack complex that can lyse invading bacteria. The more specific adaptive immune response, which responds against pathogens that bypass the innate immune response, is triggered when activated antigen-presenting cells migrate to lymphoid tissue. In lymph nodes, antigen-presenting cells present processed antigen to T cells, which, upon activation, play a central role in cellular immune responses at the site of infection, or assist in the activation of B cells for the generation of an antigen-specific humoral response.

Ticks acquire a blood meal over a period of days, allowing the host sufficient time to generate anti-tick immune responses. The tick, in turn, has developed mechanisms to protect itself against host inflammation and immune responses [4]. In light of the central role of the complement cascade and T and B cells in many human diseases, we focus on specific tick salivary molecules that target these responses.

Complement inhibitors.

The complement system is involved in the pathogenesis of many autoimmune diseases, including rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis, and also in ischemia-reperfusion injury as observed in acute myocardial infarction or ischemic stroke [27–29]. Inhibitors of the complement cascade are therefore of potential clinical interest. Many agents inhibit complement factor 3 (C3) convertase early in the complement cascade, but this inhibition can result in immunosuppression, impairment of opsonization, or immune complex deposition. Novel complement inhibitors should therefore preferably inhibit the complement cascade downstream of complement factor 5 (C5), allowing the upstream cascade to proceed physiologically. Early randomized controlled clinical trials studying the effect of an antibody targeting C5 in acute myocardial infarction showed promising results [30,31], although a more recent randomized controlled trial showed no beneficial effect on all-cause mortality of a C5-antibody compared to placebo [32]. A similar antibody was shown to be effective in the treatment of autoimmune diseases [33].

Tick saliva contains many molecules that specifically inhibit complement activation (Table 1) [34–38]. A promising tick complement inhibitor is the C5 activation inhibitor from the soft tick O. moubata, OMCI [34,39]. OMCI inhibits C5 activation by interfering with C5 convertase [39], and has been shown to inhibit human complement hemolytic activity and the development of pathological features in a rodent model for autoimmune myasthenia gravis [40].

B cell inhibitors.

The I. ricinus B cell inhibitory protein (BIP) is one of the tick salivary proteins that suppress proliferation of murine B cells (Table 1) [41,42]. Suppression of B cell responses benefits the tick by inhibiting specific anti-tick antibody responses that could lead to rejection by the host. In addition, B cells are unable to respond adequately to Borrelia burgdorferi antigens in the presence of BIP, suggesting that B. burgdorferi might also benefit from BIP-mediated B cell suppression. Specific inhibition of B cells has been shown to be effective in clinical studies of lymphoproliferative disorders and autoimmune diseases, such as rheumatoid arthritis and multiple sclerosis [43,44]. In order to serve as a template for novel drugs specifically targeting B cells, tick B cell inhibitors need further characterization.

T cell inhibitors.

The I. scapularis 15 kDa salivary protein, Salp15, is an example of a feeding-induced protein that inhibits the activation of T cells (Table 1) [45–49]. Salp15 specifically binds to the CD4 molecule on CD4+ T (helper) cells, which results in inhibition of T cell receptor–mediated signaling, leading to reduced interleukin-2 production and impaired T cell proliferation [46]. In an experimental mouse model of allergic airway disease, Salp15 prevented the development of atopic asthma [50], suggesting that Salp15 might be used to modulate atopic disease as well as T cell–driven autoimmune diseases. We have shown that Salp15 also inhibits inflammatory cytokine production by human monocyte-derived dendritic cells by interacting with the C-type lectin receptor DC-SIGN [51], indicating that Salp15 has the potential to modulate human adaptive immune responses. Iris, an immunosuppressive protein from I. ricinus, has been shown to modulate T cell responses through inhibition of interferon- and to inhibit interleukin-6 and tumor necrosis factor-a production by human macrophages [49]. In addition, Iris also has been shown to have anti-hemostatic effects by inhibiting several serine proteases involved in the coagulation cascade and fibrinolysis [52].

New Strategies to Prevent Tick-Borne Diseases

Understanding the importance of specific tick salivary proteins for attachment to the host and for transmission of pathogens may permit us to develop new strategies (e.g., anti-tick vaccines) for preventing tick-borne diseases. The idea of a tick-antigen-based vaccine is supported by the observation that repeated exposure of certain animals to tick bites results in an inability of ticks to successfully take a blood meal [45]. These animals, as well as humans who develop hypersensitivity after repeated tick bites [49], are less likely to be infected by tick-borne pathogens [53]. Ideally, an anti-tick vaccine would protect against infestation by a wide range of tick species and prevent transmission of multiple tick-borne pathogens. Discussing all tick antigens that have been assessed in vaccination trials is beyond the scope of this article. For an overview of the current stage of development of anti-tick vaccines, there is an excellent review available [54]. An interesting example of an anti-tick vaccine that also protects against the transmission of a tick-borne pathogen is a vaccine targeting the salivary cement protein, 64P, from the tick Rhipicephalus appendiculatus [55,56]. Tick feeding on animals immunized with truncated recombinant forms of 64P (64TRP) resulted in local inflammatory responses and protection against infestation by a wide range of tick species [56]. Importantly, 64TRP-vaccinated mice challenged with tick-borne encephalitis virus (the most important human vector-borne viral infection in Europe [57]) through tick bite were protected from lethal encephalitis [55].

Proteins that enhance tick feeding may also modulate host immune responses to pathogens, thus playing a double role in transmission. For example, an I. scapularis tick can introduce both Salp15 and B. burgdorferi into the host skin. As described earlier, Salp15 may enhance tick feeding by inhibiting host immune responses to tick antigens. In addition, the B. burgdorferi outer surface protein C (OspC) has been shown to bind to Salp15 in tick saliva [5]. This binding acts as a shield that protects the spirochete against the host immune response (Figure 2). Salp15 would therefore be a candidate to consider for immunization studies. Also, the pleiotropic protein Iris, that not only modulates T cell responses, but also specifically disrupts coagulation [52], could be an interesting candidate. Recently, it was shown that vaccinating rabbits with Iris partially protected these rabbits from tick infestations [58].

thumbnail
Figure 2. Diagram Showing How an Anti-Salp15 Vaccine Could Prevent Transmission of B. burgdorferi

During tick feeding and early mammalian infection, B. burgdorferi expresses OspC, which binds to Salp15 in tick saliva. This binding acts as a shield and protects the spirochete from killing by the host. In addition, Salp15 has been shown to directly inhibit dendritic cell and T cell activation, which could facilitate tick feeding. Salp15 antibodies are likely to bind to Salp15 that has previously bound to OspC on the surface of B. burgdorferi in the tick salivary gland and could thereby enhance clearance by host phagocytic immune cells. Obviously, the Salp15 antibodies would need to recognize a Salp15 epitope other than the epitope that is required for binding of Salp15 to OspC. Similarly, if anti-Salp15 antibodies were to bind to free Salp15, they could neutralize the immunosuppressive effects of Salp15, which could hamper tick feeding and thereby transmission of B. burgdorferi from the tick to the host. Lastly, if anti-Salp15 antibodies were to inhibit binding of Salp15 to Borrelia OspC, this would render the spirochete susceptible to pre-existing or newly generated immunoglobulins. Importantly, Salp15 was originally identified by screening of a tick salivary gland cDNA expression library with tick immune rabbit sera, suggesting that antibodies against Salp15 may participate in tick rejection.

DC, dendritic cell; MHC, major histocompatibility complex; MF, macrophage; TCR, T cell receptor.

https://doi.org/10.1371/journal.pmed.0050043.g002

Conclusion

Tick saliva is a potential source for novel pharmacological agents that could be useful for clinical practice. Future research must confirm whether these specific and potent molecules, with promising results in animal models and in human ex vivo experiments, are effective in humans in vivo. The molecules discussed are only a selection of the many physiologically active molecules that have been identified and characterized. However, this selection illustrates the impressive resourcefulness that ticks display to modulate host processes, and demonstrates how we could use these molecules to our benefit. Undoubtedly, future research on tick–host and tick–host–pathogen interactions will reveal even more potential molecules that could be used in clinical practice.

Acknowledgments

We thank Rick Henderik for his help with the extensive literature search for publications relevant for the discussed topics and Christian Stutzer for the generation of Figure 2.

References

  1. 1. Steere AC, Coburn J, Glickstein L (2004) The emergence of Lyme disease. J Clin Invest 113: 1093–1101.AC SteereJ. CoburnL. Glickstein2004The emergence of Lyme disease.J Clin Invest11310931101
  2. 2. Dumler JS, Choi KS, Garcia-Garcia JC, Barat NS, Scorpio DG, et al. (2005) Human granulocytic anaplasmosis and Anaplasma phagocytophilum. Emerg Infect Dis 11: 1828–1834.JS DumlerKS ChoiJC Garcia-GarciaNS BaratDG Scorpio2005Human granulocytic anaplasmosis and Anaplasma phagocytophilum.Emerg Infect Dis1118281834
  3. 3. Brossard M, Wikel SK (2004) Tick immunobiology. Parasitology 129(Suppl): S161–S176.M. BrossardSK Wikel2004Tick immunobiology.Parasitology129SupplS161S176
  4. 4. Valenzuela JG (2004) Exploring tick saliva: from biochemistry to ‘sialomes’ and functional genomics. Parasitology 129(Suppl): S83–S94.JG Valenzuela2004Exploring tick saliva: from biochemistry to ‘sialomes’ and functional genomics.Parasitology129SupplS83S94
  5. 5. Ramamoorthi N, Narasimhan S, Pal U, Bao F, Yang XF, et al. (2005) The Lyme disease agent exploits a tick protein to infect the mammalian host. Nature 436: 573–577.N. RamamoorthiS. NarasimhanU. PalF. BaoXF Yang2005The Lyme disease agent exploits a tick protein to infect the mammalian host.Nature436573577
  6. 6. Fukumoto S, Sakaguchi T, You M, Xuan X, Fujisaki K (2006) Tick troponin I-like molecule is a potent inhibitor for angiogenesis. Microvasc Res 71: 218–221.S. FukumotoT. SakaguchiM. YouX. XuanK. Fujisaki2006Tick troponin I-like molecule is a potent inhibitor for angiogenesis.Microvasc Res71218221
  7. 7. Maritz-Olivier C, Stutzer C, Jongejan F, Neitz AW, Gaspar AR (2007) Tick anti-hemostatics: targets for future vaccines and therapeutics. Trends Parasitol 23: 397–407.C. Maritz-OlivierC. StutzerF. JongejanAW NeitzAR Gaspar2007Tick anti-hemostatics: targets for future vaccines and therapeutics.Trends Parasitol23397407
  8. 8. Levi M (2005) New antithrombotics in the treatment of thromboembolic disease. Eur J Intern Med 16: 230–237.M. Levi2005New antithrombotics in the treatment of thromboembolic disease.Eur J Intern Med16230237
  9. 9. Waxman L, Smith DE, Arcuri KE, Vlasuk GP (1990) Tick anticoagulant peptide (TAP) is a novel inhibitor of blood coagulation factor Xa. Science 248: 593–596.L. WaxmanDE SmithKE ArcuriGP Vlasuk1990Tick anticoagulant peptide (TAP) is a novel inhibitor of blood coagulation factor Xa.Science248593596
  10. 10. Rezaie AR (2004) Kinetics of factor Xa inhibition by recombinant tick anticoagulant peptide: both active site and exosite interactions are required for a slow- and tight-binding inhibition mechanism. Biochemistry 43: 3368–3375.AR Rezaie2004Kinetics of factor Xa inhibition by recombinant tick anticoagulant peptide: both active site and exosite interactions are required for a slow- and tight-binding inhibition mechanism.Biochemistry4333683375
  11. 11. Schaffer LW, Davidson JT, Vlasuk GP, Siegl PK (1991) Antithrombotic efficacy of recombinant tick anticoagulant peptide. A potent inhibitor of coagulation factor Xa in a primate model of arterial thrombosis. Circulation 84: 1741–1748.LW SchafferJT DavidsonGP VlasukPK Siegl1991Antithrombotic efficacy of recombinant tick anticoagulant peptide. A potent inhibitor of coagulation factor Xa in a primate model of arterial thrombosis.Circulation8417411748
  12. 12. Sitko GR, Ramjit DR, Stabilito II, Lehman D, Lynch JJ, et al. (1992) Conjunctive enhancement of enzymatic thrombolysis and prevention of thrombotic reocclusion with the selective factor Xa inhibitor, tick anticoagulant peptide. Comparison to hirudin and heparin in a canine model of acute coronary artery thrombosis. Circulation 85: 805–815.GR SitkoDR RamjitII StabilitoD. LehmanJJ Lynch1992Conjunctive enhancement of enzymatic thrombolysis and prevention of thrombotic reocclusion with the selective factor Xa inhibitor, tick anticoagulant peptide. Comparison to hirudin and heparin in a canine model of acute coronary artery thrombosis.Circulation85805815
  13. 13. Vlasuk GP, Ramjit D, Fujita T, Dunwiddie CT, Nutt EM, et al. (1991) Comparison of the in vivo anticoagulant properties of standard heparin and the highly selective factor Xa inhibitors antistasin and tick anticoagulant peptide (TAP) in a rabbit model of venous thrombosis. Thromb Haemost 65: 257–262.GP VlasukD. RamjitT. FujitaCT DunwiddieEM Nutt1991Comparison of the in vivo anticoagulant properties of standard heparin and the highly selective factor Xa inhibitors antistasin and tick anticoagulant peptide (TAP) in a rabbit model of venous thrombosis.Thromb Haemost65257262
  14. 14. Stoll P, Bassler N, Hagemeyer CE, Eisenhardt SU, Chen YC, et al. (2007) Targeting ligand-induced binding sites on GPIIb/IIIa via single-chain antibody allows effective anticoagulation without bleeding time prolongation. Arterioscler Thromb Vasc Biol 27: 1206–1212.P. StollN. BasslerCE HagemeyerSU EisenhardtYC Chen2007Targeting ligand-induced binding sites on GPIIb/IIIa via single-chain antibody allows effective anticoagulation without bleeding time prolongation.Arterioscler Thromb Vasc Biol2712061212
  15. 15. Joubert AM, Louw AI, Joubert F, Neitz AW (1998) Cloning, nucleotide sequence and expression of the gene encoding factor Xa inhibitor from the salivary glands of the tick, Ornithodoros savignyi. Exp Appl Acarol 22: 603–619.AM JoubertAI LouwF. JoubertAW Neitz1998Cloning, nucleotide sequence and expression of the gene encoding factor Xa inhibitor from the salivary glands of the tick, Ornithodoros savignyi.Exp Appl Acarol22603619
  16. 16. Narasimhan S, Montgomery RR, Deponte K, Tschudi C, Marcantonio N, et al. (2004) Disruption of Ixodes scapularis anticoagulation by using RNA interference. Proc Natl Acad Sci U S A 101: 1141–1146.S. NarasimhanRR MontgomeryK. DeponteC. TschudiN. Marcantonio2004Disruption of Ixodes scapularis anticoagulation by using RNA interference.Proc Natl Acad Sci U S A10111411146
  17. 17. Francischetti IM, Mather TN, Ribeiro JM (2004) Penthalaris, a novel recombinant five-Kunitz tissue factor pathway inhibitor (TFPI) from the salivary gland of the tick vector of Lyme disease, Ixodes scapularis. Thromb Haemost 91: 886–898.IM FrancischettiTN MatherJM Ribeiro2004Penthalaris, a novel recombinant five-Kunitz tissue factor pathway inhibitor (TFPI) from the salivary gland of the tick vector of Lyme disease, Ixodes scapularis.Thromb Haemost91886898
  18. 18. Francischetti IM, Valenzuela JG, Andersen JF, Mather TN, Ribeiro JM (2002) Ixolaris, a novel recombinant tissue factor pathway inhibitor (TFPI) from the salivary gland of the tick, Ixodes scapularis: identification of factor X and factor Xa as scaffolds for the inhibition of factor VIIa/tissue factor complex. Blood 99: 3602–3612.IM FrancischettiJG ValenzuelaJF AndersenTN MatherJM Ribeiro2002Ixolaris, a novel recombinant tissue factor pathway inhibitor (TFPI) from the salivary gland of the tick, Ixodes scapularis: identification of factor X and factor Xa as scaffolds for the inhibition of factor VIIa/tissue factor complex.Blood9936023612
  19. 19. Nazareth RA, Tomaz LS, Ortiz-Costa S, Atella GC, Ribeiro JM, et al. (2006) Antithrombotic properties of Ixolaris, a potent inhibitor of the extrinsic pathway of the coagulation cascade. Thromb Haemost 96: 7–13.RA NazarethLS TomazS. Ortiz-CostaGC AtellaJM Ribeiro2006Antithrombotic properties of Ixolaris, a potent inhibitor of the extrinsic pathway of the coagulation cascade.Thromb Haemost96713
  20. 20. Weitz JI, Hudoba M, Massel D, Maraganore J, Hirsh J (1990) Clot-bound thrombin is protected from inhibition by heparin-antithrombin III but is susceptible to inactivation by antithrombin III-independent inhibitors. J Clin Invest 86: 385–391.JI WeitzM. HudobaD. MasselJ. MaraganoreJ. Hirsh1990Clot-bound thrombin is protected from inhibition by heparin-antithrombin III but is susceptible to inactivation by antithrombin III-independent inhibitors.J Clin Invest86385391
  21. 21. Ciprandi A, de Oliveira SK, Masuda A, Horn F, Termignoni C (2006) Boophilus microplus: its saliva contains microphilin, a small thrombin inhibitor. Exp Parasitol 114: 40–46.A. CiprandiSK de OliveiraA. MasudaF. HornC. Termignoni2006Boophilus microplus: its saliva contains microphilin, a small thrombin inhibitor.Exp Parasitol1144046
  22. 22. Iwanaga S, Okada M, Isawa H, Morita A, Yuda M, et al. (2003) Identification and characterization of novel salivary thrombin inhibitors from the ixodidae tick, Haemaphysalis longicornis. Eur J Biochem 270: 1926–1934.S. IwanagaM. OkadaH. IsawaA. MoritaM. Yuda2003Identification and characterization of novel salivary thrombin inhibitors from the ixodidae tick, Haemaphysalis longicornis.Eur J Biochem27019261934
  23. 23. Mans BJ, Louw AI, Neitz AW (2002) Amino acid sequence and structure modeling of savignin, a thrombin inhibitor from the tick, Ornithodoros savignyi. Insect Biochem Mol Biol 32: 821–828.BJ MansAI LouwAW Neitz2002Amino acid sequence and structure modeling of savignin, a thrombin inhibitor from the tick, Ornithodoros savignyi.Insect Biochem Mol Biol32821828
  24. 24. van de Locht A, Stubbs MT, Bode W, Friedrich T, Bollschweiler C, et al. (1996) The ornithodorin-thrombin crystal structure, a key to the TAP enigma. EMBO J 15: 6011–6017.A. van de LochtMT StubbsW. BodeT. FriedrichC. Bollschweiler1996The ornithodorin-thrombin crystal structure, a key to the TAP enigma.EMBO J1560116017
  25. 25. Koh CY, Kazimirova M, Trimnell A, Takac P, Labuda M, et al. (2007) Variegin, a novel fast and tight binding thrombin inhibitor from the tropical bont tick. J Biol Chem 282: 29101–29113.CY KohM. KazimirovaA. TrimnellP. TakacM. Labuda2007Variegin, a novel fast and tight binding thrombin inhibitor from the tropical bont tick.J Biol Chem2822910129113
  26. 26. Lincoff AM, Kleiman NS, Kereiakes DJ, Feit F, Bittl JA, et al. (2004) Long-term efficacy of bivalirudin and provisional glycoprotein IIb/IIIa blockade vs heparin and planned glycoprotein IIb/IIIa blockade during percutaneous coronary revascularization: REPLACE-2 randomized trial. JAMA 292: 696–703.AM LincoffNS KleimanDJ KereiakesF. FeitJA Bittl2004Long-term efficacy of bivalirudin and provisional glycoprotein IIb/IIIa blockade vs heparin and planned glycoprotein IIb/IIIa blockade during percutaneous coronary revascularization: REPLACE-2 randomized trial.JAMA292696703
  27. 27. Walport MJ (2001) Complement. Second of two parts. N Engl J Med 344: 1140–1144.MJ Walport2001Complement. Second of two parts.N Engl J Med34411401144
  28. 28. Walport MJ (2001) Complement. First of two parts. N Engl J Med 344: 1058–1066.MJ Walport2001Complement. First of two parts.N Engl J Med34410581066
  29. 29. Mollnes TE, Song WC, Lambris JD (2002) Complement in inflammatory tissue damage and disease. Trends Immunol 23: 61–64.TE MollnesWC SongJD Lambris2002Complement in inflammatory tissue damage and disease.Trends Immunol236164
  30. 30. Granger CB, Mahaffey KW, Weaver WD, Theroux P, Hochman JS, et al. (2003) Pexelizumab, an anti-C5 complement antibody, as adjunctive therapy to primary percutaneous coronary intervention in acute myocardial infarction: the COMplement inhibition in Myocardial infarction treated with Angioplasty (COMMA) trial. Circulation 108: 1184–1190.CB GrangerKW MahaffeyWD WeaverP. TherouxJS Hochman2003Pexelizumab, an anti-C5 complement antibody, as adjunctive therapy to primary percutaneous coronary intervention in acute myocardial infarction: the COMplement inhibition in Myocardial infarction treated with Angioplasty (COMMA) trial.Circulation10811841190
  31. 31. Mahaffey KW, Van de WF, Shernan SK, Granger CB, Verrier ED, et al. (2006) Effect of pexelizumab on mortality in patients with acute myocardial infarction or undergoing coronary artery bypass surgery: a systematic overview. Am Heart J 152: 291–296.KW MahaffeyWF Van deSK ShernanCB GrangerED Verrier2006Effect of pexelizumab on mortality in patients with acute myocardial infarction or undergoing coronary artery bypass surgery: a systematic overview.Am Heart J152291296
  32. 32. Armstrong PW, Granger CB, Adams PX, Hamm C, Holmes D Jr, et al. (2007) Pexelizumab for acute ST-elevation myocardial infarction in patients undergoing primary percutaneous coronary intervention: a randomized controlled trial. JAMA 297: 43–51.PW ArmstrongCB GrangerPX AdamsC. HammD. Holmes Jr2007Pexelizumab for acute ST-elevation myocardial infarction in patients undergoing primary percutaneous coronary intervention: a randomized controlled trial.JAMA2974351
  33. 33. Hillmen P, Young NS, Schubert J, Brodsky RA, Socie G, et al. (2006) The complement inhibitor eculizumab in paroxysmal nocturnal hemoglobinuria. N Engl J Med 355: 1233–1243.P. HillmenNS YoungJ. SchubertRA BrodskyG. Socie2006The complement inhibitor eculizumab in paroxysmal nocturnal hemoglobinuria.N Engl J Med35512331243
  34. 34. Nunn MA, Sharma A, Paesen GC, Adamson S, Lissina O, et al. (2005) Complement inhibitor of C5 activation from the soft tick Ornithodoros moubata. J Immunol 174: 2084–2091.MA NunnA. SharmaGC PaesenS. AdamsonO. Lissina2005Complement inhibitor of C5 activation from the soft tick Ornithodoros moubata.J Immunol17420842091
  35. 35. Schroeder H, Daix V, Gillet L, Renauld JC, Vanderplasschen A (2007) The paralogous salivary anti-complement proteins IRAC I and IRAC II encoded by Ixodes ricinus ticks have broad and complementary inhibitory activities against the complement of different host species. Microbes Infect 9: 247–250.H. SchroederV. DaixL. GilletJC RenauldA. Vanderplasschen2007The paralogous salivary anti-complement proteins IRAC I and IRAC II encoded by Ixodes ricinus ticks have broad and complementary inhibitory activities against the complement of different host species.Microbes Infect9247250
  36. 36. Tyson K, Elkins C, Patterson H, Fikrig E, de Silva A (2007) Biochemical and functional characterization of Salp20, an Ixodes scapularis tick salivary protein that inhibits the complement pathway. Insect Mol Biol 16: 469–479.K. TysonC. ElkinsH. PattersonE. FikrigA. de Silva2007Biochemical and functional characterization of Salp20, an Ixodes scapularis tick salivary protein that inhibits the complement pathway.Insect Mol Biol16469479
  37. 37. Valenzuela JG, Charlab R, Mather TN, Ribeiro JM (2000) Purification, cloning, and expression of a novel salivary anticomplement protein from the tick, Ixodes scapularis. J Biol Chem 275: 18717–18723.JG ValenzuelaR. CharlabTN MatherJM Ribeiro2000Purification, cloning, and expression of a novel salivary anticomplement protein from the tick, Ixodes scapularis.J Biol Chem2751871718723
  38. 38. Ribeiro JM (1987) Ixodes dammini: salivary anti-complement activity. Exp Parasitol 64: 347–353.JM Ribeiro1987Ixodes dammini: salivary anti-complement activity.Exp Parasitol64347353
  39. 39. Roversi P, Lissina O, Johnson S, Ahmat N, Paesen GC, et al. (2007) The structure of OMCI, a novel lipocalin inhibitor of the complement system. J Mol Biol 369: 784–793.P. RoversiO. LissinaS. JohnsonN. AhmatGC Paesen2007The structure of OMCI, a novel lipocalin inhibitor of the complement system.J Mol Biol369784793
  40. 40. Hepburn NJ, Williams AS, Nunn MA, Chamberlain-Banoub JC, Hamer J, et al. (2007) In vivo characterization and therapeutic efficacy of a C5-specific inhibitor from the soft tick Ornithodoros moubata. J Biol Chem 282: 8292–8299.NJ HepburnAS WilliamsMA NunnJC Chamberlain-BanoubJ. Hamer2007In vivo characterization and therapeutic efficacy of a C5-specific inhibitor from the soft tick Ornithodoros moubata.J Biol Chem28282928299
  41. 41. Hannier S, Liversidge J, Sternberg JM, Bowman AS (2004) Characterization of the B-cell inhibitory protein factor in Ixodes ricinus tick saliva: a potential role in enhanced Borrelia burgdoferi transmission. Immunology 113: 401–408.S. HannierJ. LiversidgeJM SternbergAS Bowman2004Characterization of the B-cell inhibitory protein factor in Ixodes ricinus tick saliva: a potential role in enhanced Borrelia burgdoferi transmission.Immunology113401408
  42. 42. Yu D, Liang J, Yu H, Wu H, Xu C, et al. (2006) A tick B-cell inhibitory protein from salivary glands of the hard tick, Hyalomma asiaticum asiaticum. Biochem Biophys Res Commun 343: 585–590.D. YuJ. LiangH. YuH. WuC. Xu2006A tick B-cell inhibitory protein from salivary glands of the hard tick, Hyalomma asiaticum asiaticum.Biochem Biophys Res Commun343585590
  43. 43. Bugatti S, Codullo V, Caporali R, Montecucco C (2007) B cells in rheumatoid arthritis. Autoimmun Rev 6: 482–487.S. BugattiV. CodulloR. CaporaliC. Montecucco2007B cells in rheumatoid arthritis.Autoimmun Rev6482487
  44. 44. Klawiter EC, Cross AH (2007) B cells: no longer the nondominant arm of multiple sclerosis. Curr Neurol Neurosci Rep 7: 231–238.EC KlawiterAH Cross2007B cells: no longer the nondominant arm of multiple sclerosis.Curr Neurol Neurosci Rep7231238
  45. 45. Anguita J, Ramamoorthi N, Hovius JW, Das S, Thomas V, et al. (2002) Salp15, an ixodes scapularis salivary protein, inhibits CD4(+) T cell activation. Immunity 16: 849–859.J. AnguitaN. RamamoorthiJW HoviusS. DasV. Thomas2002Salp15, an ixodes scapularis salivary protein, inhibits CD4(+) T cell activation.Immunity16849859
  46. 46. Garg R, Juncadella IJ, Ramamoorthi N, Ashish , Ananthanarayanan SK, et al. (2006) Cutting edge: CD4 is the receptor for the tick saliva immunosuppressor, Salp15. J Immunol 177: 6579–6583.R. GargIJ JuncadellaN. RamamoorthiAshishSK Ananthanarayanan2006Cutting edge: CD4 is the receptor for the tick saliva immunosuppressor, Salp15.J Immunol17765796583
  47. 47. Gillespie RD, Dolan MC, Piesman J, Titus RG (2001) Identification of an IL-2 binding protein in the saliva of the Lyme disease vector tick, Ixodes scapularis. J Immunol 166: 4319–4326.RD GillespieMC DolanJ. PiesmanRG Titus2001Identification of an IL-2 binding protein in the saliva of the Lyme disease vector tick, Ixodes scapularis.J Immunol16643194326
  48. 48. Kotsyfakis M, Sa-Nunes A, Francischetti IM, Mather TN, Andersen JF, et al. (2006) Antiinflammatory and immunosuppressive activity of sialostatin L, a salivary cystatin from the tick Ixodes scapularis. J Biol Chem 281: 26298–26307.M. KotsyfakisA. Sa-NunesIM FrancischettiTN MatherJF Andersen2006Antiinflammatory and immunosuppressive activity of sialostatin L, a salivary cystatin from the tick Ixodes scapularis.J Biol Chem2812629826307
  49. 49. Leboulle G, Crippa M, Decrem Y, Mejri N, Brossard M, et al. (2002) Characterization of a novel salivary immunosuppressive protein from Ixodes ricinus ticks. J Biol Chem 277: 10083–10089.G. LeboulleM. CrippaY. DecremN. MejriM. Brossard2002Characterization of a novel salivary immunosuppressive protein from Ixodes ricinus ticks.J Biol Chem2771008310089
  50. 50. Paveglio SA, Allard J, Mayette J, Whittaker LA, Juncadella I, et al. (2007) The tick salivary protein, salp15, inhibits the development of experimental asthma. J Immunol 178: 7064–7071.SA PaveglioJ. AllardJ. MayetteLA WhittakerI. Juncadella2007The tick salivary protein, salp15, inhibits the development of experimental asthma.J Immunol17870647071
  51. 51. Hovius JWR, de Jong MAWP, den Dunnen J, Litjens M, Fikrig E, et al. (2008) Salp15 binding to DC-SIGN inhibits dendritic cell function by impairing nucleosome remodeling and decreasing mRNA stability of pro-inflammatory cytokines. PLoS Pathog 4: e31.JWR HoviusMAWP de JongJ. den DunnenM. LitjensE. Fikrig2008Salp15 binding to DC-SIGN inhibits dendritic cell function by impairing nucleosome remodeling and decreasing mRNA stability of pro-inflammatory cytokines.PLoS Pathog4e31
  52. 52. Prevot PP, Adam B, Boudjeltia KZ, Brossard M, Lins L, et al. (2006) Anti-hemostatic effects of a serpin from the saliva of the tick Ixodes ricinus. J Biol Chem 281: 26361–26369.PP PrevotB. AdamKZ BoudjeltiaM. BrossardL. Lins2006Anti-hemostatic effects of a serpin from the saliva of the tick Ixodes ricinus.J Biol Chem2812636126369
  53. 53. Burke G, Wikel SK, Spielman A, Telford SR, McKay K, et al. (2005) Hypersensitivity to ticks and Lyme disease risk. Emerg Infect Dis 11: 36–41.G. BurkeSK WikelA. SpielmanSR TelfordK. McKay2005Hypersensitivity to ticks and Lyme disease risk.Emerg Infect Dis113641
  54. 54. de la Fuente J, Kocan KM (2006) Strategies for development of vaccines for control of ixodid tick species. Parasite Immunol 28: 275–283.J. de la FuenteKM Kocan2006Strategies for development of vaccines for control of ixodid tick species.Parasite Immunol28275283
  55. 55. Labuda M, Trimnell AR, Ličková M, Kazimírová M, Davies GM, et al. (2006) An antivector vaccine protects against a lethal vector-borne pathogen. PLoS Pathog 2: e27.M. LabudaAR TrimnellM. LičkováM. KazimírováGM Davies2006An antivector vaccine protects against a lethal vector-borne pathogen.PLoS Pathog2e27
  56. 56. Trimnell AR, Davies GM, Lissina O, Hails RS, Nuttall PA (2005) A cross-reactive tick cement antigen is a candidate broad-spectrum tick vaccine. Vaccine 23: 4329–4341.AR TrimnellGM DaviesO. LissinaRS HailsPA Nuttall2005A cross-reactive tick cement antigen is a candidate broad-spectrum tick vaccine.Vaccine2343294341
  57. 57. Kunze U, Baumhackl U, Bretschneider R, Chmelik V, Grubeck-Loebenstein B, et al. (2005) The Golden Agers and Tick-borne encephalitis. Conference report and position paper of the International Scientific Working Group on Tick-borne encephalitis. Wien Med Wochenschr 155: 289–294.U. KunzeU. BaumhacklR. BretschneiderV. ChmelikB. Grubeck-Loebenstein2005The Golden Agers and Tick-borne encephalitis. Conference report and position paper of the International Scientific Working Group on Tick-borne encephalitis.Wien Med Wochenschr155289294
  58. 58. Prevot PP, Couvreur B, Denis V, Brossard M, Vanhamme L, et al. (2007) Protective immunity against Ixodes ricinus induced by a salivary serpin. Vaccine 25: 3284–3292.PP PrevotB. CouvreurV. DenisM. BrossardL. Vanhamme2007Protective immunity against Ixodes ricinus induced by a salivary serpin.Vaccine2532843292