Tick saliva has been extensively studied in the context of tick-host interactions because it is involved in host homeostasis modulation and microbial pathogen transmission to the host. Accumulated knowledge about the tick saliva composition at the molecular level has revealed that serine protease inhibitors play a key role in the tick-host interaction. Serpins are one highly expressed group of protease inhibitors in tick salivary glands, their expression can be induced during tick blood-feeding, and they have many biological functions at the tick-host interface. Indeed, tick serpins have an important role in inhibiting host hemostatic processes and in the modulation of the innate and adaptive immune responses of their vertebrate hosts. Tick serpins have also been studied as potential candidates for therapeutic use and vaccine development. In this review, we critically summarize the current state of knowledge about the biological role of tick serpins in shaping tick-host interactions with emphasis on the mechanisms by which they modulate host immunity. Their potential use in drug and vaccine development is also discussed.

• Keywords
• anti-tick vaccine, immunomodulation, serpins, therapeutic effects, tick host interaction, tick saliva,
• MeSH
• Serine Proteinase Inhibitors physiology   MeSH
• Ticks * metabolism   MeSH
• Serpins * metabolism   MeSH
• Salivary Glands metabolism   MeSH
• Saliva metabolism   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Serine Proteinase Inhibitors MeSH
• Serpins * MeSH

Hemostatic disorders are caused either by platelet-related dysfunctions, defective blood coagulation, or by a combination of both, leading to an increased susceptibility to cardiovascular diseases (CVD) and other related illnesses. The unique specificity of anticoagulants from hematophagous arthropods, such as ticks, suggests that tick saliva holds great promise for discovering new treatments for these life-threatening diseases. In this study, we combined in silico and in vitro analyses to characterize the first recombinant serpin, herein called Dromaserpin, from the sialotranscriptome of the Hyalomma dromedarii tick. Our in silico data described Dromaserpin as a secreted protein of ~43 kDa with high similarities to previously characterized inhibitory serpins. The recombinant protein (rDromaserpin) was obtained as a well-structured monomer, which was tested using global blood coagulation and platelet aggregation assays. With this approach, we confirmed rDromaserpin anticoagulant activity as it significantly delayed plasma clotting in activated partial thromboplastin time and thrombin time assays. The profiling of proteolytic activity shows its capacity to inhibit thrombin in the micromolar range (0.2 to 1 μM) and in the presence of heparin this inhibition was clearly increased. It was also able to inhibit Kallikrein, FXIa and slightly FXIIa, with no significant effect on other factors. In addition, the rDromaserpin inhibited thrombin-induced platelet aggregation. Taken together, our data suggest that rDromaserpin deserves to be further investigated as a potential candidate for developing therapeutic compounds targeting disorders related to blood clotting and/or platelet aggregation.

• Keywords
• Hyalomma dromedarii, anticoagulants, salivary glands, serpin, thrombin inhibitor,
• MeSH
• Anticoagulants chemistry   metabolism   MeSH
• Phylogeny MeSH
• Blood Coagulation drug effects   MeSH
• Ixodidae metabolism   MeSH
• Protein Conformation MeSH
• Models, Molecular MeSH
• Computer Simulation MeSH
• Amino Acid Sequence MeSH
• Serpins chemistry   metabolism   pharmacology   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Anticoagulants MeSH
• Serpins MeSH

Iripin-5 is the main Ixodes ricinus salivary serpin, which acts as a modulator of host defence mechanisms by impairing neutrophil migration, suppressing nitric oxide production by macrophages and altering complement functions. Iripin-5 influences host immunity and shows high expression in the salivary glands. Here, the crystal structure of Iripin-5 in the most thermodynamically stable state of serpins is described. In the reactive-centre loop, the main substrate-recognition site of Iripin-5 is likely to be represented by Arg342, which implies the targeting of trypsin-like proteases. Furthermore, a computational structural analysis of selected Iripin-5-protease complexes together with interface analysis revealed the most probable residues of Iripin-5 involved in complex formation.

• Keywords
• Iripin-5, Ixodes ricinus, X-ray structure, serine protease inhibitors, serpins, tick saliva,
• MeSH
• Anti-Inflammatory Agents * chemistry   isolation & purification   MeSH
• Erythrocytes MeSH
• Enzyme Inhibitors * chemistry   isolation & purification   MeSH
• Ixodes metabolism   MeSH
• Rabbits MeSH
• Cells, Cultured MeSH
• Macrophages MeSH
• Mice, Inbred C57BL MeSH
• Mice MeSH
• Neutrophils MeSH
• Serpins * chemistry   isolation & purification   MeSH
• Animals MeSH
• Check Tag
• Rabbits MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Anti-Inflammatory Agents * MeSH
• Enzyme Inhibitors * MeSH
• Serpins * MeSH

Tick saliva is a rich source of pharmacologically and immunologically active molecules. These salivary components are indispensable for successful blood feeding on vertebrate hosts and are believed to facilitate the transmission of tick-borne pathogens. Here we present the functional and structural characterization of Iripin-3, a protein expressed in the salivary glands of the tick Ixodes ricinus, a European vector of tick-borne encephalitis and Lyme disease. Belonging to the serpin superfamily of protease inhibitors, Iripin-3 strongly inhibited the proteolytic activity of serine proteases kallikrein and matriptase. In an in vitro setup, Iripin-3 was capable of modulating the adaptive immune response as evidenced by reduced survival of mouse splenocytes, impaired proliferation of CD4+ T lymphocytes, suppression of the T helper type 1 immune response, and induction of regulatory T cell differentiation. Apart from altering acquired immunity, Iripin-3 also inhibited the extrinsic blood coagulation pathway and reduced the production of pro-inflammatory cytokine interleukin-6 by lipopolysaccharide-stimulated bone marrow-derived macrophages. In addition to its functional characterization, we present the crystal structure of cleaved Iripin-3 at 1.95 Å resolution. Iripin-3 proved to be a pluripotent salivary serpin with immunomodulatory and anti-hemostatic properties that could facilitate tick feeding via the suppression of host anti-tick defenses. Physiological relevance of Iripin-3 activities observed in vitro needs to be supported by appropriate in vivo experiments.

• Keywords
• Ixodes ricinus, X-ray crystallography, adaptive immunity, blood coagulation, inflammation, saliva, serpin, tick,
• MeSH
• Adaptive Immunity drug effects   MeSH
• Lymphocyte Activation drug effects   MeSH
• Anticoagulants isolation & purification   pharmacology   MeSH
• Cytokines metabolism   MeSH
• Blood Coagulation drug effects   MeSH
• Insect Proteins isolation & purification   pharmacology   MeSH
• Immunologic Factors isolation & purification   pharmacology   MeSH
• Protease Inhibitors isolation & purification   pharmacology   MeSH
• Ixodes metabolism   MeSH
• Rabbits MeSH
• Cells, Cultured MeSH
• Humans MeSH
• Lymphocytes drug effects   immunology   metabolism   MeSH
• Guinea Pigs MeSH
• Mice, Inbred C3H MeSH
• Mice, Inbred C57BL MeSH
• Mice, Transgenic MeSH
• Mice MeSH
• Cell Proliferation drug effects   MeSH
• Spleen drug effects   immunology   metabolism   MeSH
• Salivary Proteins and Peptides isolation & purification   pharmacology   MeSH
• Saliva metabolism   MeSH
• Animals MeSH
• Check Tag
• Rabbits MeSH
• Humans MeSH
• Guinea Pigs MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Anticoagulants MeSH
• Cytokines MeSH
• Insect Proteins MeSH
• Immunologic Factors MeSH
• Protease Inhibitors MeSH
• Salivary Proteins and Peptides MeSH

The publication of the first tick sialome (salivary gland transcriptome) heralded a new era of research of tick protease inhibitors, which represent important constituents of the proteins secreted via tick saliva into the host. Three major groups of protease inhibitors are secreted into saliva: Kunitz inhibitors, serpins, and cystatins. Kunitz inhibitors are anti-hemostatic agents and tens of proteins with one or more Kunitz domains are known to block host coagulation and/or platelet aggregation. Serpins and cystatins are also anti-hemostatic effectors, but intriguingly, from the translational perspective, also act as pluripotent modulators of the host immune system. Here we focus especially on this latter aspect of protease inhibition by ticks and describe the current knowledge and data on secreted salivary serpins and cystatins and their role in tick-host-pathogen interaction triad. We also discuss the potential therapeutic use of tick protease inhibitors.

• Keywords
• cystatins, immunomodulation, protease inhibitors, serpins, tick-host interaction,
• MeSH
• Cystatins physiology   therapeutic use   MeSH
• Immunomodulation MeSH
• Protease Inhibitors classification   metabolism   therapeutic use   MeSH
• Serine Proteinase Inhibitors physiology   therapeutic use   MeSH
• Host-Parasite Interactions MeSH
• Ticks metabolism   MeSH
• Humans MeSH
• Serpins physiology   therapeutic use   MeSH
• Saliva enzymology   metabolism   MeSH
• Transcriptome MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Cystatins MeSH
• Protease Inhibitors MeSH
• Serine Proteinase Inhibitors MeSH
• Serpins MeSH