The Ixodes scapularis salivary protein, salp15, prevents the association of HIV-1 gp120 and CD4

Tick Salivary Compounds for Targeted Immunomodulatory Therapy

Immunodeficiency disorders and autoimmune diseases are common, but a lack of effective targeted drugs and the side-effects of existing drugs have stimulated interest in finding therapeutic alternatives. Naturally derived substances are a recognized source of novel drugs, and tick saliva is increasingly recognized as a rich source of bioactive molecules with specific functions. Ticks use their saliva to overcome the innate and adaptive host immune systems. Their saliva is a rich cocktail of molecules including proteins, peptides, lipid derivatives, and recently discovered non-coding RNAs that inhibit or modulate vertebrate immune reactions. A number of tick saliva and/or salivary gland molecules have been characterized and shown to be promising candidates for drug development for vertebrate immune diseases. However, further validation of these molecules at the molecular, cellular, and organism levels is now required to progress lead candidates to clinical testing. In this paper, we review the data on the immuno-pharmacological aspects of tick salivary compounds characterized in vitro and/or in vivo and present recent findings on non-coding RNAs that might be exploitable as immunomodulatory therapies.

Salp15, a Multifunctional Protein From Tick Saliva With Potential Pharmaceutical Effects

Ixodes ticks are the main vectors for a number of zoonotic diseases, including Lyme disease. Ticks secrete saliva directly into a mammalian host while feeding on the host's blood. This action serves to modulate host immunity and coagulation, thus allowing ticks to attach and feed upon their host. One of the most extensively studied components of tick saliva is Salp15. Research has shown that this protein binds specifically to CD4 molecules on the surface of T lymphocytes, interferes with TCR-mediated signaling transduction, inhibits CD4+ T cell activation and proliferation, and impedes the secretion of interleukin 2 (IL-2). Salp15 also binds specifically to dendritic cell dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) to up-regulate the expression of CD73 in regulatory T cells. Collectively, these findings render this salivary protein a potential candidate for a range of therapeutic applications. Here, we discuss our current understanding of Salp15 and the mechanisms that might be used to treat disease.

The Use of Tick Salivary Proteins as Novel Therapeutics

The last three decades of research into tick salivary components have revealed several proteins with important pharmacological and immunological activities. Two primary interests have driven research into tick salivary secretions: the search for suitable pathogen transmission blocking or “anti-tick” vaccine candidates and the search for novel therapeutics derived from tick salivary components. Intensive basic research in the field of tick salivary gland transcriptomics and proteomics has identified several major protein families that play important roles in tick feeding and overcoming vertebrate anti-tick responses. Moreover, these families contain members with unrealized therapeutic potential. Here we review the major tick salivary protein families exploitable in medical applications such as immunomodulation, inhibition of hemostasis and inflammation. Moreover, we discuss the potential, opportunities, and challenges in searching for novel tick-derived drugs.

An Immunosuppressant Peptide from the Hard Tick Amblyomma variegatum

Ixodid ticks are well known for spreading transmitted tick-borne pathogens while being attached to their hosts for almost 1-2 weeks to obtain blood meals. Thus, they must secrete many immunosuppressant factors to combat the hosts' immune system. In the present work, we investigated an immunosuppressant peptide of the hard tick Amblyomma variegatum. This peptide, named amregulin, is composed of 40 residues with an amino acid sequence of HLHMHGNGATQVFKPRLVLKCPNAAQLIQPGKLQRQLLLQ. A cDNA of the precursor peptide was obtained from the National Center for Biotechnology Information (NCBI, Bethesda, MD, USA). In rat splenocytes, amregulin exerts significant anti-inflammatory effects by inhibiting the secretion of inflammatory factors in vitro, such as tumor necrosis factor-alpha (TNF-α), interleukin-1 (IL-1), interleukin-8 (IL-8) and interferon-gamma (IFN-γ). In rat splenocytes, treated with amregulin, compared to lipopolysaccharide (LPS) alone, the inhibition of the above inflammatory factors was significant at all tested concentrations (2, 4 and 8 µg/mL). Amregulin shows strong free radical scavenging and antioxidant activities (5, 10 and 20 µg/mL) in vitro. Amregulin also significantly inhibits adjuvant-induced paw inflammation in mouse models in vivo. This peptide may facilitate the ticks' successful blood feeding and may lead to host immunotolerance of the tick. These findings have important implications for the understanding of tick-host interactions and the co-evolution between ticks and the viruses that they bear.

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

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

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.

Phages and HIV-1: from display to interplay

The complex hide-and-seek game between HIV-1 and the host immune system has impaired the development of an efficient vaccine. In addition, the high variability of the virus impedes the long-term control of viral replication by small antiviral drugs. For more than 20 years, phage display technology has been intensively used in the field of HIV-1 to explore the epitope landscape recognized by monoclonal and polyclonal HIV-1-specific antibodies, thereby providing precious data about immunodominant and neutralizing epitopes. In parallel, biopanning experiments with various combinatorial or antibody fragment libraries were conducted on viral targets as well as host receptors to identify HIV-1 inhibitors. Besides these applications, phage display technology has been applied to characterize the enzymatic specificity of the HIV-1 protease. Phage particles also represent valuable alternative carriers displaying various HIV-1 antigens to the immune system and eliciting antiviral responses. This review presents and summarizes the different studies conducted with regard to the nature of phage libraries, target display mode and biopanning procedures.

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.