Babesial vector tick defensin against Babesia sp. parasites

Transfusion-transmitted Babesia spp.: a changing landscape of epidemiology, regulation, and risk mitigation

Babesia spp. are tick-borne parasites with a global distribution and diversity of vertebrate hosts. Over the next several decades, climate change is expected to impact humans, vectors, and vertebrate hosts and change the epidemiology of Babesia. Although humans are dead-end hosts for tick-transmitted Babesia, human-to-human transmission of Babesia spp. from transfusion of red blood cells and whole blood-derived platelet concentrates has been reported. In most patients, transfusion-transmitted Babesia (TTB) results in a moderate-to-severe illness. Currently, in North America, most cases of TTB have been described in the United States. TTB cases outside North America are rare, but case numbers may change over time with increased recognition of babesiosis and as the epidemiology of Babesia is impacted by climate change. Therefore, TTB is a concern of microbiologists working in blood operator settings, as well as in clinical settings where transfusion occurs. Microbiologists play an important role in deploying blood donor screening assays in Babesia endemic regions, identifying changing risks for Babesia in non-endemic areas, investigating recipients of blood products for TTB, and drafting TTB policies and guidelines. In this review, we provide an overview of the clinical presentation and epidemiology of TTB. We identify approaches and technologies to reduce the risk of collecting blood products from Babesia-infected donors and describe how investigations of TTB are undertaken. We also describe how microbiologists in Babesia non-endemic regions can assess for changing risks of TTB and decide when to focus on laboratory-test-based approaches or pathogen reduction to reduce TTB risk.

The tick saliva peptide HIDfsin2 promotes the tick-borne virus SFTSV replication in vitro by enhancing p38 signal pathway

Pathogens co-evolved with ticks to facilitate blood collection and pathogen transmission. Although tick saliva was recently found to be rich in bioactive peptides, it is still elusive which saliva peptide promotes virus transmission and which pathways are invovled. Here, we used a saliva peptide HIDfsin2 and a severe fever with thrombocytopenia syndrome virus (SFTSV) both carried by the tick Haemaphysalis longicornis to elucidate the relationship between tick saliva components and tick-borne viruses. HIDfsin2 was found to promote the replication of SFTSV in a dose-dependent manner in vitro. HIDfsin2 was further revealed to MKK3/6-dependently magnify the activation of p38 MAPK. The overexpression, knockdown and phosphorylation site mutation of p38α indicated that p38 MAPK activation facilitated SFTSV infection in A549 cells. Moreover, the blockade of p38 MAPK activation significantly suppressed SFTSV replication. Differently, HIDfsin2 or pharmacological inhibition of p38 MAPK activation had no effect on a mosquito-borne Zika virus (ZIKV). All these results showed that HIDfsin2 specifically promoted SFTSV replication through the MKK3/6-dependent enhancement of p38 MAPK activation. Our study provides a new perspective on the transmission of tick-borne viruses under natural conditions, and supports that the blockade of p38 MAPK activation can be a promising strategy against the mortal tick-borne virus SFTSV.

Animal venoms: a novel source of anti-Toxoplasma gondii drug candidates

Toxoplasma gondii (T. gondii) is a nucleated intracellular parasitic protozoan with a broad host selectivity. It causes toxoplasmosis in immunocompromised or immunodeficient patients. The currently available treatments for toxoplasmosis have significant side effects as well as certain limitations, and the development of vaccines remains to be explored. Animal venoms are considered to be an important source of novel antimicrobial agents. Some peptides from animal venoms have amphipathic alpha-helix structures. They inhibit the growth of pathogens by targeting membranes to produce lethal pores and cause membrane rupture. Venom molecules generally possess immunomodulatory properties and play key roles in the suppression of pathogenic organisms. Here, we summarized literatures of the last 15 years on the interaction of animal venom peptides with T. gondii and attempt to explore the mechanisms of their interaction with parasites that involve membrane and organelle damage, immune response regulation and ion homeostasis. Finally, we analyzed some limitations of venom peptides for drug therapy and some insights into their development in future studies. It is hoped that more research will be stimulated to turn attention to the medical value of animal venoms in toxoplasmosis.

Defensins as a promising class of tick antimicrobial peptides: a scoping review

Background

Ticks are hematophagous parasites that transmit an extensive range of pathogens to their vertebrate hosts. Ticks can destroy invading microorganisms or alleviate infection via their rudimentary but orchestrated innate immune system. Antimicrobial peptides (AMPs) are important components of tick innate immunity. Among these humoral effector molecules, defensins are well-studied and widely identified in various species of Ixodidae (hard ticks) and Argasidae (soft ticks). This review was aimed at presenting the characterization of tick defensins from structure-based taxonomic status to antimicrobial function.

Main text

All published papers written in English from 2001 to May 2022 were searched through PubMed and Web of Science databases with the combination of relevant terms on tick defensins. Reports on identification and characterization of tick defensins were included. Of the 329 entries retrieved, 57 articles were finally eligible for our scoping review.

Tick defensins mainly belong to the antibacterial ancient invertebrate-type defensins of the cis-defensins superfamily. They are generally small, cationic, and amphipathic, with six cysteine residues forming three intra-molecular disulfide bonds. Tick defensins primarily target membranes of a variety of pathogens, including Gram-positive and Gram-negative bacteria, fungi, viruses, and protozoa. Since tick defensins have a high degree of variability, we summarize their common biological properties and enumerate representative peptides. Along with the various and potent antimicrobial activities, the role of tick defensins in determining vector competence is discussed.

Conclusions

Due to their broad-spectrum antimicrobial activities, tick defensins are considered novel candidates or targets for controlling infectious diseases.

Graphical Abstract

Dynamics of Theileria equi Infection in Rhipicephalus (Boophilus) microplus during the Parasitic Phase in a Chronically Infected Horse

Experimental studies have demonstrated that Rhipicephalus (Boophilus) microplus transmits Theileria equi to horses. However, the degree and dynamics of this protozoan infection in the vector’s organism have not been fully elucidated. Therefore, this study aimed to evaluate the infection rate and parasitic load of T. equi in R. (B.) microplus, the infection dynamics in this arthropod during experimental infestation in a horse chronically infected with T. equi, and to evaluate the trans-stadial and intrastadial transmission competence of T. equi by R. (B.) microplus. The experimental infestation period of R. (B.) microplus on the horse was 33 days, but males were found on the animal up to 60 days post-infestation. After the fifth day post-infestation, ticks and equine blood were collected every two days. Whole ticks from the same developmental stage collected in the same day were pooled. Adult ticks were dissected to extract salivary glands and gut. DNA extraction was performed for all the samples, and they were then submitted to qPCRs for T. equi diagnosis. Freshly molted nymphs collected as larvae in the horse and freshly molted males and females collected as nymphs in the horse showed equal to or greater than 75% positivity for T. equi, indicating a strong possibility of trans-stadial transmission. The longest permanence of the male ticks on the horse associated with the high positivity rate of this type of sample for T. equi indicate that the male may play a role in the intrastadial transmission of T. equi to infection-free horses. The salivary glands displayed 77.78% positivity for T. equi and presented a higher infection rate at the end of the experimental period (100% from 29 to 33 days post-infection). This study shows that R. (B.) microplus has high T. equi infection rates and that the infection rate and parasitic load increased over the experimental period. These findings confirm the importance of chronically infected horses with T. equi as a source of infection for R. (B.) microplus.

Identification and Functional Analysis of a Defensin CcDef2 from Coridius chinensis

Coridius chinensis belongs to Dinidoridae, Hemiptera. Previous studies have indicated that C. chinensis contains abundant polypeptides with antibacterial and anticancer activities. Antimicrobial peptides (AMPs), as endogenous peptides with immune function, play an indispensable role in the process of biological development and immunity. AMPs have become one of the most potential substitutes for antibiotics due to their small molecular weight and broad-spectrum antimicrobial activity. In this study, a defensin CcDef2 from C. chinensis was characterized based on bioinformatics and functional analyses. The mature peptide of CcDef2 is a typical cationic peptide composed of 43 amino acid residues with five cations, and contains three intramolecular disulfide bonds and a typical cysteine-stabilized αβ motif in defensins. Phylogenetic analysis showed that CcDef2 belongs to the insect defensin family. Analysis of gene expression patterns showed that CcDef2 was expressed throughout developmental stages of C. chinensis with high levels at the nymphal stage and in adult tissues tested with the highest level in the fat body. In addition, the CcDef2 expression was significantly upregulated in adults infected by bacteria. After expressed in Escherichia coli BL21(DE3) and renatured, the recombinant CcDef2 showed a significant antibacterial effect on three kinds of Gram-positive bacteria. These results indicate that CcDef2 is an excellent antibacterial peptide and a highly effective immune effector in the innate immunity of C. chinensis. This study provides a foundation for further understanding the function of CcDef2 and developing new antimicrobial drugs.

Antifungal activity and mode of action of synthetic peptides derived from the tick OsDef2 defensin

Candida albicans is the principal opportunistic fungal pathogen in nosocomial settings and resistance to antifungal drugs is on the rise. Antimicrobial peptides from natural sources are promising novel therapeutics against C. albicans. OsDef2 defensin was previously found to be active against only Gram-positive bacteria, whereas derived fragments Os and its cysteine-free analogue, Os-C, are active against Gram-positive and Gram-negative bacteria at low micromolar concentrations. In this study, OsDef2-derived analogues and fragments were screened for anticandidal activity with the aim to identify peptides with antifungal activity and in so doing obtain a better understanding of the structural requirements for activity and modes of action. Os, Os-C and Os(11-22)NH₂ , a Os-truncated carboxy-terminal-amidated fragment, had the most significant antifungal activities, with minimum fungicidal concentrations (MFCs) in the micromolar range (6-28 μM). C. albicans killing was rapid and occurred within 30-60 min. Further investigations showed all three peptides interacted with cell wall derived polysaccharides while both Os and Os(11-22)NH₂ permeabilized fungal liposomes. Confocal laser scanning microscopy confirmed that Os-C and Os(11-22)NH₂ could enter the cytosol of live cells and subsequent findings suggest that the uptake of Os and Os-C, in contrast to Os(11-22)NH₂ , is energy dependent. Although Os, Os-C and Os(11-22)NH₂ induced the production of reactive oxygen species (ROS), co-incubation with ascorbic acid revealed that only ROS generated by Os-C and to a lesser extent Os(11-22)NH₂ resulted in cell death. Overall, Os, Os-C and Os(11-22)NH₂ are promising candidacidal agents.

Response of Leucine-Rich Repeat Domain-Containing Protein in Haemaphysalis longicornis to Babesia microti Infection and Its Ligand Identification

Haemaphysalis longicornis is a blood-feeding hard tick known for transmitting a variety of pathogens, including Babesia How the parasites in the imbibed blood become anchored in the midgut of ticks is still unknown. Leucine-rich repeat domain (LRR)-containing protein, which is associated with the innate immune reaction and conserved in many species, has been detected in H. longicornis and has previously been indicated in inhibiting the growth of Babesia gibsoni However, the detailed mechanism is unknown. In this study, one of the ligands for LRR from H. longicornis (HlLRR) was identified in Babesia microti, designated BmActin, using glutathione transferase (GST) pulldown experiments and immunofluorescence assays. Moreover, RNA interference of HlLRR led to a decrease in the BmActin mRNA expression in the midgut of fully engorged ticks which fed on B. microti-infected mice. We also found that the expression level of the innate immune molecules in H. longicornis, defensin, antimicrobial peptides (AMPs), and lysozyme, were downregulated after the knockdown of HlLRR. However, subolesin expression was upregulated. These results indicate that HlLRR not only recognizes BmActin but may also modulate innate immunity in ticks to influence Babesia growth, which will further benefit the development of anti-Babesia vaccines or drugs.

Induced Transient Immune Tolerance in Ticks and Vertebrate Host: A Keystone of Tick-Borne Diseases?

Ticks and tick transmitted infectious agents are increasing global public health threats due to increasing abundance, expanding geographic ranges of vectors and pathogens, and emerging tick-borne infectious agents. Greater understanding of tick, host, and pathogen interactions will contribute to development of novel tick control and disease prevention strategies. Tick-borne pathogens adapt in multiple ways to very different tick and vertebrate host environments and defenses. Ticks effectively pharmacomodulate by its saliva host innate and adaptive immune defenses. In this review, we examine the idea that successful synergy between tick and tick-borne pathogen results in host immune tolerance that facilitates successful tick infection and feeding, creates a favorable site for pathogen introduction, modulates cutaneous and systemic immune defenses to establish infection, and contributes to successful long-term infection. Tick, host, and pathogen elements examined here include interaction of tick innate immunity and microbiome with tick-borne pathogens; tick modulation of host cutaneous defenses prior to pathogen transmission; how tick and pathogen target vertebrate host defenses that lead to different modes of interaction and host infection status (reservoir, incompetent, resistant, clinically ill); tick saliva bioactive molecules as important factors in determining those pathogens for which the tick is a competent vector; and, the need for translational studies to advance this field of study. Gaps in our understanding of these relationships are identified, that if successfully addressed, can advance the development of strategies to successfully disrupt both tick feeding and pathogen transmission.

Natural Occurrence in Venomous Arthropods of Antimicrobial Peptides Active against Protozoan Parasites

Arthropoda is a phylum of invertebrates that has undergone remarkable evolutionary radiation, with a wide range of venomous animals. Arthropod venom is a complex mixture of molecules and a source of new compounds, including antimicrobial peptides (AMPs). Most AMPs affect membrane integrity and produce lethal pores in microorganisms, including protozoan pathogens, whereas others act on internal targets or by modulation of the host immune system. Protozoan parasites cause some serious life-threatening diseases among millions of people worldwide, mostly affecting the poorest in developing tropical regions. Humans can be infected with protozoan parasites belonging to the genera Trypanosoma, Leishmania, Plasmodium, and Toxoplasma, responsible for Chagas disease, human African trypanosomiasis, leishmaniasis, malaria, and toxoplasmosis. There is not yet any cure or vaccine for these illnesses, and the current antiprotozoal chemotherapeutic compounds are inefficient and toxic and have been in clinical use for decades, which increases drug resistance. In this review, we will present an overview of AMPs, the diverse modes of action of AMPs on protozoan targets, and the prospection of novel AMPs isolated from venomous arthropods with the potential to become novel clinical agents to treat protozoan-borne diseases.

Antibacterial and antifungal activity of defensins from the Australian paralysis tick, Ixodes holocyclus

Tick innate immunity involves humoral and cellular responses. Among the humoral effector molecules in ticks are the defensins which are a family of small peptides with a conserved γ-core motif that is crucial for their antimicrobial activity. Defensin families have been identified in several hard and soft tick species. However, little is known about the presence and antimicrobial activity of defensins from the Australian paralysis tick Ixodes holocyclus. In this study the I. holocyclus transcriptome was searched for the presence of defensins. Unique and non-redundant defensin sequences were identified and designated as holosins 1 - 5. The antimicrobial activity of holosins 2 and 3 and of the predicted γ-cores of holosins 1-4 (HoloTickCores 1-4), was assessed using Gram-negative and Gram-positive bacteria as well as the fungus Fusarium graminearum and the yeast Candida albicans. All holosins had molecular features that are conserved in other tick defensins. Furthermore holosins 2 and 3 were very active against the Gram-positive bacteria Staphylococcus aureus and Listeria grayi. Holosins 2 and 3 were also active against F. graminearum and C. albicans and 5 μM of peptide abrogate the growth of these microorganisms. The activity of the synthetic γ-cores was lower than that of the mature defensins apart from HoloTickCore 2 which had activity comparable to mature holosin 2 against the Gram-negative bacterium Escherichia coli. This study reveals the presence of a multigene defensin family in I. holocyclus with wide antimicrobial activity.

Counterattacking the tick bite: towards a rational design of anti-tick vaccines targeting pathogen transmission

Hematophagous arthropods are responsible for the transmission of a variety of pathogens that cause disease in humans and animals. Ticks of the Ixodes ricinus complex are vectors for some of the most frequently occurring human tick-borne diseases, particularly Lyme borreliosis and tick-borne encephalitis virus (TBEV). The search for vaccines against these diseases is ongoing. Efforts during the last few decades have primarily focused on understanding the biology of the transmitted viruses, bacteria and protozoans, with the goal of identifying targets for intervention. Successful vaccines have been developed against TBEV and Lyme borreliosis, although the latter is no longer available for humans. More recently, the focus of intervention has shifted back to where it was initially being studied which is the vector. State of the art technologies are being used for the identification of potential vaccine candidates for anti-tick vaccines that could be used either in humans or animals. The study of the interrelationship between ticks and the pathogens they transmit, including mechanisms of acquisition, persistence and transmission have come to the fore, as this knowledge may lead to the identification of critical elements of the pathogens' life-cycle that could be targeted by vaccines. Here, we review the status of our current knowledge on the triangular relationships between ticks, the pathogens they carry and the mammalian hosts, as well as methods that are being used to identify anti-tick vaccine candidates that can prevent the transmission of tick-borne pathogens.

Vectors of Babesiosis

Babesiosis, caused by piroplasmid protozoans in the genus Babesia, is arguably the most important vector-borne disease of livestock and companion animals and is growing in importance as a zoonosis. Ixodid ticks were identified as vectors more than a hundred years ago, but the particular tick species transmitting some significant pathogens are still unknown. Moreover, it is only recently that the complexity of the pathogen-tick relationship has been revealed as a result of studies enabled by gene expression and RNA interference methodology. In this article, we provide details of demonstrated and incriminated vectors, maps of the current knowledge of vector distribution, a summary of established features of the pathogen life cycle in the vector, and an outline of molecular research on pathogen-tick relationships. The article concludes with a discussion of vector ecology and disease epidemiology in a global-change context and with suggestions for future research.

Insect Antimicrobial Peptides, a Mini Review

Antimicrobial peptides (AMPs) are crucial effectors of the innate immune system. They provide the first line of defense against a variety of pathogens. AMPs display synergistic effects with conventional antibiotics, and thus present the potential for combined therapies. Insects are extremely resistant to bacterial infections. Insect AMPs are cationic and comprise less than 100 amino acids. These insect peptides exhibit an antimicrobial effect by disrupting the microbial membrane and do not easily allow microbes to develop drug resistance. Currently, membrane mechanisms underlying the antimicrobial effects of AMPs are proposed by different modes: the barrel-stave mode, toroidal-pore, carpet, and disordered toroidal-pore are the typical modes. Positive charge quantity, hydrophobic property and the secondary structure of the peptide are important for the antibacterial activity of AMPs. At present, several structural families of AMPs from insects are known (defensins, cecropins, drosocins, attacins, diptericins, ponericins, metchnikowins, and melittin), but new AMPs are frequently discovered. We reviewed the biological effects of the major insect AMPs. This review will provide further information that facilitates the study of insect AMPs and shed some light on novel microbicides.

A comprehensive review on past, present and future aspects of canine theileriosis

Canine theileriosis is a notorious tick borne piroplasmid infection of wild and domestic canines. The causative agent has not yet been accurately classified. PCR studies revealed that causative agent resembles to Theileria genus and thus provisionally named as Theileria annae. The other Theileria species reported in canines is Theileria annulata, Theileria equi and unnamed Theileria specie. This emergent canine infection is considered to be endemic in most of the European countries. However in Asia this disease has not been reported till date. The vectors responsible for transmission of this disease have not been determined. It has been suggested that DNA of Theileria annae has been detected in hard tick Ixodes hexagonus in Northwestern Spain and several other tick species. Clinically canine theileriosis is characterized by severe weakness, fever, hemoglobinuria and anemia. Recently atovaquone or buparvaquone plus azithromycin therapy showed better clinical efficacy. This comprehensive review is intended to summarize the current knowledge on prevalence and epidemiology of canine theileriosis in different countries of the world and associated tick vectors.

Hemolymph defensin from the hard tick Haemaphysalis longicornis attacks Gram-positive bacteria

Ticks are key vectors of some important diseases of humans and animals. Although they are carriers of disease agents, the viability and development of ticks are not harmed by the infectious agents due to their innate immunity. Antimicrobial peptides directly protect hosts against pathogenic agents such as viruses, bacteria, and parasites. Among the identified and characterized antimicrobial peptides, defensins have been considerably well studied. Defensins are commonly found among fungi, plants, invertebrates, and vertebrates. The sequence of the tick hemolymph defensin (HEdefensin) gene from the hard tick Haemaphysalis longicornis was analyzed after identification and cloning from a cDNA library. HEdefensin has a predicted molecular mass of 8.15 kDa including signal peptides and a theoretical isoelectric point of 9.48. Six cysteine residues were also identified in the amino acids. The synthetic HEdefensin peptide only showed antibacterial activity against Gram-positive bacteria such as Micrococcus luteus. A fluorescence propidium iodide exclusion assay also showed that HEdefensin increased the membrane permeability of M. luteus. Additionally, an indirect fluorescent antibody test showed that HEdefensin binds to M. luteus. These results suggested that HEdefensin strongly affects the innate immunity of ticks against Gram-positive bacteria.

Deciphering Babesia-Vector Interactions

Understanding host-pathogen-tick interactions remains a vitally important issue that might be better understood by basic research focused on each of the dyad interplays. Pathogens gain access to either the vector or host during tick feeding when ticks are confronted with strong hemostatic, inflammatory and immune responses. A prominent example of this is the Babesia spp.—tick—vertebrate host relationship. Babesia spp. are intraerythrocytic apicomplexan organisms spread worldwide, with a complex life cycle. The presence of transovarial transmission in almost all the Babesia species is the main difference between their life cycle and that of other piroplasmida. With more than 100 species described so far, Babesia are the second most commonly found blood parasite of mammals after trypanosomes. The prevalence of Babesia spp. infection is increasing worldwide and is currently classified as an emerging zoonosis. Babesia microti and Babesia divergens are the most frequent etiological agents associated with human babesiosis in North America and Europe, respectively. Although the Babesia-tick system has been extensively researched, the currently available prophylactic and control methods are not efficient, and chemotherapeutic treatment is limited. Studying the molecular changes induced by the presence of Babesia in the vector will not only elucidate the strategies used by the protozoa to overcome mechanical and immune barriers, but will also contribute toward the discovery of important tick molecules that have a role in vector capacity. This review provides an overview of the identified molecules involved in Babesia-tick interactions, with an emphasis on the fundamentally important ones for pathogen acquisition and transmission.

Complete Molecular and Immunoprotective Characterization of Babesia microti Enolase

The apicomplexan Babesia microti is the primary causative agent of human babesiosis, one of the most broadly distributed tick-borne diseases worldwide. B. microti undergoes a complex lifecycle within both the mammalian host and the tick vector, and employs several different specific molecular mechanisms to enter host cells. Enolase, the key glycolytic enzyme in intracellular glucose metabolism, can also be expressed on the parasite’s outer surface, binds to human plasminogen, and coordinates apicomplexan parasite invasion of host cells, however, it lacks sorting sequences or lipoprotein anchor sites. In the present study, we isolated the coding gene of B. microti enolase (BmEno), expressed it within E. coli and purified the recombinant BmEno protein (rBmEno). Consequently, we confirmed cytoplasmic and surface localization of BmEno via immunofluorescence, and demonstrated that rBmEno catalyzes the dehydration of 2-phospho-D-glycerate to phosphoenolpyruvate. Moreover, our results showed that rBmEno binds to human plasminogen, and that the lysine analog ε-aminocaproic acid significantly inhibited this binding. Furthermore plasminogen bound to rBmEno converts to active plasmin. Additionally, actively immunizing mice with rBmEno could evoke a partial protective immunity against B. microti infection following challenge. In conclusion, B. microti enolase is a multifunctional cytoplasmic protein which is also expressed at the parasitic outer surface, facilitates binding to host plasminogen, and could partially protect hosts against parasite infection.

Characterization and antiviral activity of a newly identified defensin-like peptide, HEdefensin, in the hard tick Haemaphysalis longicornis

Tick defensins are antimicrobial peptides that play a major role in the innate immunity of ticks by providing a direct antimicrobial defense. In this study, we identified and characterized a defensin-like encoding gene, HEdefensin, from the expressed sequence tags (EST) database of hemolymph from the hard tick Haemaphysalis longicornis. Expression of the gene in whole adult ticks and in different organs was upregulated during blood feeding, though not after Langat virus (LGTV) challenge. A synthetic HEdefensin peptide demonstrated significant virucidal activity against LGTV but not against an adenovirus in co-incubation virucidal assays. Moreover, the RNAi-mediated gene silencing of HEdefensin did not significantly affect the virus titer as compared to the control group. The data reported here have established the in vitro virucidal activity of the peptide against LGTV. However, its role in the innate antiviral immunity of H. longicornis remains to be explored, and further studies are needed to fully evaluate the potential biological activities of the peptide against bacteria, fungi or parasites.

Establishing a reference array for the CS-αβ superfamily of defensive peptides

BACKGROUND

"Invertebrate defensins" belong to the cysteine-stabilized alpha-beta (CS-αβ), also known as the scorpion toxin-like, superfamily. Some other peptides belonging to this superfamily of defensive peptides are indistinguishable from "defensins," but have been assigned other names, making it unclear what, if any, criteria must be met to qualify as an "invertebrate defensin." In addition, there are other groups of defensins in invertebrates and vertebrates that are considered to be evolutionarily unrelated to those in the CS-αβ superfamily. This complicates analyses and discussions of this peptide group. This paper investigates the criteria for classifying a peptide as an invertebrate defensin, suggests a reference cysteine array that may be helpful in discussing peptides in this superfamily, and proposes that the superfamily (rather than the name "defensin") is the appropriate context for studying the evolution of invertebrate defensins with the CS-αβ fold.

METHODS

CS-αβ superfamily sequences were identified from previous literature and BLAST searches of public databases. Sequences were retrieved from databases, and the relevant motifs were identified and used to create a conceptual alignment to a ten-cysteine reference array. Amino acid sequences were aligned in MEGA6 with manual adjustments to ensure accurate alignment of cysteines. Phylogenetic analyses were performed in MEGA6 (maximum likelihood) and MrBayes (Bayesian).

RESULTS

Across invertebrate taxa, the term "defensin" is not consistently applied based on number of cysteines, cysteine spacing pattern, spectrum of antimicrobial activity, or phylogenetic relationship. The analyses failed to reveal any criteria that unify "invertebrate defensins" and differentiate them from other defensive peptides in the CS-αβ superfamily. Sequences from various groups within the CS-αβ superfamily of defensive peptides can be described by a ten-cysteine reference array that aligns their defining structural motifs.

CONCLUSIONS

The proposed ten-cysteine reference array can be used in addition to current nomenclature to compare sequences in the CS-αβ superfamily and clarify their features relative to one another. This will facilitate analysis and discussion of "invertebrate defensins" in an appropriate evolutionary context, rather than relying on nomenclature.

Activity of tick antimicrobial peptide from Ixodes persulcatus (persulcatusin) against cell membranes of drug-resistant Staphylococcus aureus

Persulcatusin (IP), which is an antimicrobial peptide found in Ixodes persulcatus midgut, is active against Gram-positive bacteria such as Staphylococcus aureus. Multidrug-resistant bacteria in particular methicillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) are a worldwide clinical concern. In the present study, to explore the potential of IP as a new agent against multidrug-resistant S. aureus infections, we evaluated the antimicrobial activity of IP against multidrug-resistant S. aureus strains by MIC₉₀, morphological observation with scanning electron microscope (SEM), and the calcein leakage assay of membrane integrity. Among the six antimicrobial peptides used in this study, IP exhibited the lowest MIC₉₀ values for both vancomycin-susceptible and -resistant S. aureus strains. The IP MIC₉₀ against a VISA strain was equivalent to vancomycin, while the MIC₉₀ against VRSA was relatively low. SEM observations indicated that bacterial cells exposed to IP were crumpled and showed prominent structural changes. Moreover, IP influenced the cell membranes of both MRSA and VRSA in a mere 5 min, leading to leakage of the preloaded calcein. Although a VISA strain was resistant to the action of IP on cell membrane, the MIC₉₀ of IP was lower than that of Nisin, suggesting that IP had another bactericidal mechanism in addition to cell membrane attack. Our results indicate that the synthetic tick antimicrobial peptide, IP exhibits strong antibacterial activity against multidrug-resistant S. aureus strains, including VRSA, via both cell membrane attack and another unknown mechanism. IP represents a promising candidate for a new anti-VRSA therapy.

A review of canine babesiosis: the European perspective

Canine babesiosis is a significant tick-borne disease caused by various species of the protozoan genus Babesia. Although it occurs worldwide, data relating to European infections have now been collected for many years. These data have boosted the publication record and increased our working knowledge of these protozoan parasites. Both the large and small forms of Babesia species (B. canis, B. vogeli, B. gibsoni, and B. microti-like isolates also referred to as "B. vulpes" and "Theileria annae") infect dogs in Europe, and their geographical distribution, transmission, clinical signs, treatment, and prognosis vary widely for each species. The goal of this review is to provide veterinary practitioners with practical guidelines for the diagnosis, treatment and prevention of babesiosis in European dogs. Our hope is that these guidelines will answer the most frequently asked questions posed by veterinary practitioners.

Identification, structural characterisation and expression analysis of a defensin gene from the tiger beetle Calomera littoralis (Coleoptera: Cicindelidae)

In this study, a defensin gene (Clit-Def) has been characterised in the tiger beetle Calomera littoralis for the first time. Bioinformatic analysis showed that the gene has an open reading frame of 246bp that contains a 46 amino acid mature peptide. The phylogenetic analysis showed a high variability in the coleopteran defensins analysed. The Clit-Def mature peptide has the features to be involved in the antimicrobial function: a predicted cationic isoelectric point of 8.94, six cysteine residues that form three disulfide bonds, and the typical cysteine-stabilized α-helix β-sheet (CSαβ) structural fold. Real time quantitative PCR analysis showed that Clit-Def was upregulated in the different body parts analysed after infection with lipopolysaccharides of Escherichia coli, and also indicated that has an expression peak at 12h post infection. The expression patterns of Clit-Def suggest that this gene plays important roles in the humoral system in the adephagan beetle Calomera littoralis.

Antiparasitic peptides

: The most important parasitic diseases, malaria, leishmaniasis, trypanosomiasis, and schistosomiasis, are a great burden to mankind, threatening the life of millions of people worldwide and mostly affecting the poorest. Because drug resistance is increasing and vaccines are rarely available, novel chemotherapeutic compounds are necessary in order to treat these devastating diseases. Insects serve as vectors of many human parasitic diseases and have been shown to express a huge variety of antimicrobial peptides (AMPs). Therefore, research activity on insect-derived AMPs has been increasing in the last 40 years. This chapter summarizes the current state of research on the possible role of AMPs as potential chemotherapeutic compounds against human parasitic diseases. As a representative antimicrobial peptide with antiparasitic activity, the structure of insect defensin A is shown [PDB accession code: 1ICA]. The molecule is surrounded by schematic representations of the human pathogenic parasites Plasmodium, Leishmania and Trypanosoma.

Functional structure and antimicrobial activity of persulcatusin, an antimicrobial peptide from the hard tick Ixodes persulcatus

Background

Antimicrobial peptides (AMPs) are considered promising candidates for the development of novel anti-infective agents. In arthropods such as ticks, AMPs form the first line of defense against pathogens in the innate immune response. Persulcatusin (IP) was found in the Ixodes persulcatus midgut, and its amino acid sequence was reported. However, the complete structure of IP has not been identified. We evaluated the relation between structural features and antimicrobial activity of IP, and its potential as a new anti-methicillin-resistant Staphylococcus aureus (MRSA) agent.

Methods

The structure of IP was predicted using homology modeling and molecular dynamics. IP and other tick AMPs were synthesized using a solid-phase method and purified by high-performance liquid chromatography. Methicillin-susceptible S. aureus (MSSA) and MRSA were used for the minimum inhibitory concentration (MIC) test and short-time killing assay of IP and other tick peptides. The influence of IP on mammalian fibroblasts and colon epithelial cells and each cell DNA and its hemolytic activity towards human erythrocytes were also examined.

Results

In the predicted IP structure, the structure with an S-S bond was more stable than that without an S-S bond. The MIC after 24 h of incubation with IP was 0.156–1.25 μg/mL for MSSA and 0.625–2.5 μg/mL for MRSA. Compared with the mammalian antimicrobial peptide and other tick peptides, IP was highly effective against MRSA. Moreover, IP showed a dose-dependent bactericidal effect on both MSSA and MRSA after 1 h of incubation. IP had no observable effect on mammalian cell growth or morphology, on each cell DNA and on human erythrocytes.

Conclusions

We predicted the three-dimensional structure of IP and found that the structural integrity was maintained by three S-S bonds, which were energetically important for the stability and for forming α helix and β sheet. IP has cationic and amphipathic properties, which might be related to its antimicrobial activity. Furthermore, the antimicrobial activity of IP against MRSA was stronger than that of other antimicrobial peptides without apparent damage to mammalian and human cells, demonstrating its possible application as a new anti-MRSA medicine.

Virucidal activity of Haemaphysalis longicornis longicin P4 peptide against tick-borne encephalitis virus surrogate Langat virus

Background

Longicin is a defensin-like peptide, identified from the midgut epithelium of hard tick Haemaphysalis longicornis. Several studies have already shown the antimicrobial and parasiticidal activities of longicin peptide and one of its synthetic partial analogs, longicin P4. In this study, longicin peptides were tested for potential antiviral activity against Langat virus (LGTV), a tick-borne flavivirus.

Methods

Longicin P1 and P4 peptides were chemically synthesized. Antiviral activity of the longicin peptides against LGTV was evaluated through in vitro virucidal assays, wherein the antiviral efficacy was determined by reduction in number of viral foci and virus yield. Additionally, longicin P4 was also tested for its activity against human adenovirus, a non-enveloped virus. Lastly, to assess the importance of longicin on the innate antiviral immunity of H. longicornis ticks, gene silencing through RNAi was performed.

Results

Longicin P4 produced significant viral foci reduction and lower virus yield against LGTV, while longicin P1 failed to demonstrate the same results. Conversely, both longicin partial analogs (P1 and P4) did not show significant antiviral activity when tested on adenovirus. In addition, longicin-silenced ticks showed significantly higher virus titer after 7 days post-infection but a significantly lower titer was detected after an additional 14 days of observation as compared to the Luc dsRNA-injected ticks. Mortality in both groups did not show any significant difference.

Conclusion

Our results suggest that longicin P4 has in vitro antiviral activity against LGTV but not against a non-enveloped virus such as adenovirus. Likewise, though most cationic antimicrobial peptides like longicin act directly on target membranes, the exact mechanism of membrane targeting of longicin P4 in enveloped viruses, such as LGTV, requires further investigation. Lastly, while the in vitro virucidal capacity of longicin P4 was confirmed in this study, the role of the endogenous tick longicin in the antiviral defense of H. longicornis against LGTV still remains to be demonstrated.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1344-5) contains supplementary material, which is available to authorized users.

Impaired cellular immune response to injected bacteria after knockdown of ferritin genes in the hard tick Haemaphysalis longicornis

Iron is an indispensable element for most microorganisms, including many pathogenic bacteria. Iron-withholding is a known component of the innate immunity, particularly of vertebrate hosts. Ticks are vectors of multiple pathogens and reports have shown that they naturally harbor several bacterial species. Thus, tick innate immunity must be crucial in limiting bacterial population to tolerable level that will not cause adverse effects. We have previously characterized two types of the iron-binding protein ferritin (HlFER) in the hard tick Haemaphysalis longicornis, known to be a vector of some protozoan parasites and rickettsiae, and showed their antioxidant function and importance in blood feeding and reproduction. Here we examined the possible role of HlFERs in tick immunity against bacterial infection. After silencing Hlfer genes, adult ticks were injected with live enhanced green fluorescence protein-expressing Escherichia coli, and then monitored for survival rate. Hemolymph that included hemocytes was collected for microscopic examination to observe cellular immune response, and for E. coli culture to determine bacterial viability after injection in the ticks. The expression of some antimicrobial peptides in whole ticks was also analyzed by RT-PCR. Hlfer-silenced ticks had a significantly lower survival rate than control ticks after E. coli injection. Greater number of bacteria inside and outside the hemocytes and higher bacterial colony counts after culture with hemolymph were also observed in Hlfer-silenced ticks. However, no difference on the expression of antimicrobial peptides was observed. These results suggest that ferritin molecules might be important in the cellular immune response of ticks to some bacteria.

Antiplasmodial Activity Is an Ancient and Conserved Feature of Tick Defensins

Ancestral sequence reconstruction has been widely used to test evolution-based hypotheses. The genome of the European tick vector, Ixodes ricinus, encodes for defensin peptides with diverse antimicrobial activities against distantly related pathogens. These pathogens include fungi, Gram-negative, and Gram-positive bacteria, i.e., a wide antimicrobial spectrum. Ticks do not transmit these pathogens, suggesting that these defensins may act against a wide range of microbes encountered by ticks during blood feeding or off-host periods. As demonstrated here, these I. ricinus defensins are also effective against the apicomplexan parasite Plasmodium falciparum. To study the general evolution of antimicrobial activity in tick defensins, the ancestral amino acid sequence of chelicerate defensins, which existed approximately 444 million years ago, was reconstructed using publicly available scorpion and tick defensin sequences (named Scorpions-Ticks Defensins Ancestor, STiDA). The activity of STiDA was tested against P. falciparum and the same Gram-negative and Gram-positive bacteria that were used for the I. ricinus defensins. While some extant tick defensins exhibit a wide antimicrobial spectrum, the ancestral defensin showed moderate activity against one of the tested microbes, P. falciparum. This study suggests that amino acid variability and defensin family expansion increased the antimicrobial spectrum of ancestral tick defensins.

Tribolium castaneum defensins are primarily active against Gram-positive bacteria

The red flour beetle Tribolium castaneum is a destructive insect pest of stored food and feed products, and a model organism for development, evolutionary biology and immunity. The insect innate immune system includes antimicrobial peptides (AMPs) with a wide spectrum of targets including viruses, bacteria, fungi and parasites. Defensins are an evolutionarily-conserved class of AMPs and a potential new source of antimicrobial agents. In this context, we report the antimicrobial activity, phylogenetic and structural properties of three T. castaneum defensins (Def1, Def2 and Def3) and their relevance in the immunity of T. castaneum against bacterial pathogens. All three recombinant defensins showed bactericidal activity against Micrococcus luteus and Bacillus thuringiensis serovar tolworthi, but only Def1 and Def2 showed a bacteriostatic effect against Staphylococcus epidermidis. None of the defensins showed activity against the Gram-negative bacteria Escherichia coli and Pseudomonas entomophila or against the yeast Saccharomyces cerevisiae. All three defensins were transcriptionally upregulated following a bacterial challenge, suggesting a key role in the immunity of T. castaneum against bacterial pathogens. Phylogenetic analysis showed that defensins from T. castaneum, mealworms, Udo longhorn beetle and houseflies cluster within a well-defined clade of insect defensins. We conclude that T. castaneum defensins are primarily active against Gram-positive bacteria and that other AMPs may play a more prominent role against Gram-negative species.

Role of the tumor necrosis factor receptor-associated factor-type zinc finger domain containing protein 1 (TRAFD1) from the hard tick Haemaphysalis longicornis in immunity against bacterial infection

A tumor necrosis factor receptor-associated factor-type zinc finger domain containing protein 1 (TRAFD1) is a negative feedback regulator that controls excessive immune responses in vertebrates. The sequence of tick hemolymph TRAFD1 from the hard tick Haemaphysalis longicornis (HlTRAFD1) was analyzed after identification and cloning from the expressed sequence tag database. RT-PCR and Western blot analyses showed that HlTRAFD1 transcript and protein levels after blood feeding were present in all developmental stages, and the transcript level was consistently high in all organs examined from adult female ticks upon engorgement. Knockdown of HlTRAFD1 gene by RNA interference did not affect blood feeding or oviposition. However, HlTRAFD1 silencing affected the expression of the longicin gene, a defensin-like molecule, but not the lysozyme gene. Moreover, the survival rate of HlTRAFD1-silenced ticks was lower, and the number of E. coli was higher in the hemolymph and plasmatocytes after E. coli injection compared to the control group. These results suggested that HlTRAFD1 strongly affected both the humoral and cellular immunity of ticks.

Functional analysis of a novel cysteine-rich antimicrobial peptide from the salivary glands of the tick Rhipicephalus haemaphysaloides

Ticks encounter various microbes while sucking blood from an infected host and carrying these pathogens in themselves. Ticks can then transmit these pathogens to vertebrate hosts. The immune system of ticks can be stimulated to produce many bioactive molecules during feeding and pathogen invasion. Antimicrobial peptides (AMPs) are key effector molecules of a tick's immune response, as they can kill invading pathogenic microorganisms. In this study, we identified a novel cysteine-rich AMP, designated Rhamp1, in the salivary glands of unfed and fed female ticks (Rhipicephalus haemaphysaloides). Rhamp1 is encoded by a gene with an open reading frame of 333 bp, which in turn encodes a peptide of 12 kDa with a 22 amino acid residue signal peptide. The Rhamp1 protein had a pI of 8.6 and contained six conserved cysteine residues at the C-terminus. Rhamp1 shared 43% amino acid identity with a secreted cysteine-rich protein of another tick species, Ixodes scapularis. We cloned the Rhamp1 gene and attempted to express a recombinant protein using prokaryotic and eukaryotic systems, to determine its biological significance. Recombinant Rhamp1 was successfully expressed in both systems, yielding a glutathione S-transferase (GST)-tagged protein (36 kDa) from the prokaryotic system, and a polyhistidine-tagged Rhamp1 protein (14 kDa) from the eukaryotic system. Rhamp1 inhibited the activities of chymotrypsin (16%) and elastase (22%) and exerted low hemolytic activity. It also inhibited the growth of Gram-negative bacteria, including Pseudomonas aeruginosa (49%), Salmonella typhimurium (50%), and Escherichia coli (52%). Our findings suggest that Rhamp1 is a novel AMP in R. haemaphysaloides with the ability to inhibit proteinase activity.

Molecular characterization of a defensin gene from a hard tick, Dermacentor silvarum

Background

Ticks are distributed worldwide and considered as vectors of many human diseases. Tick defensins, a family of antimicrobial peptides, form the first line of defense against pathogens.

Findings

A defensin-like gene, named Ds-defensin, was identified from a cDNA library of the hard tick Dermacentor silvarum collected from northeast China. The full-length cDNA of Ds-defensin was 225 bp, encoding a 74 amino acid peptide. The nucleotide sequence of Ds-defensin shared 98.2% similarity to putative defensin from Dermacentor marginatus. RT-PCR results suggested that Ds-defensin was extensively expressed in tick salivary gland and midgut, with a higher expression level in midgut. Ds-defensin showed broad antimicrobial activity against various Gram-positive and Gram-negative bacteria, as well as the fungus Candida albicans.

Conclusions

We characterized a functional defensin from D. silvarum of China. Ds-defensin showed bactericidal activity against various Gram-positive and Gram-negative bacteria. Ds-defensin can be expected to be introduced to the medical field as a new molecule with antibacterial activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-014-0625-0) contains supplementary material, which is available to authorized users.

Tick-borne pathogens and the vector potential of ticks in China

Ticks, as obligate blood-sucking ectoparasites, attack a broad range of vertebrates and transmit a great diversity of pathogenic microorganisms. They are considered second only to mosquitoes as vectors of human disease, and the most important vector of pathogens of domestic and wild animals. Of the 117 described species in the Chinese tick fauna, 60 are known to transmit one or more diseases: 36 species isolated within China and 24 species isolated outside China. Moreover, 38 of these species carry multiple pathogens, indicating the potentially vast role of these vectors in transmitting pathogens. Spotted fever is the most common tick-borne disease, and is carried by at least 27 tick species, with Lyme disease and human granulocytic anaplasmosis ranked as the second and third most widespread tick-borne diseases, carried by 13 and 10 species, respectively. Such knowledge provides us with clues for the identification of tick-associated pathogens and suggests ideas for the control of tick-borne diseases in China. However, the numbers of tick-associated pathogens and tick-borne diseases in China are probably underestimated because of the complex distribution and great diversity of tick species in this country.

Defensins from the tick Ixodes scapularis are effective against phytopathogenic fungi and the human bacterial pathogen Listeria grayi

BACKGROUND

Ixodes scapularis is the most common tick species in North America and a vector of important pathogens that cause diseases in humans and animals including Lyme disease, anaplasmosis and babesiosis. Tick defensins have been identified as a new source of antimicrobial agents with putative medical applications due to their wide-ranging antimicrobial activities. Two multigene families of defensins were previously reported in I. scapularis. The objective of the present study was to characterise the potential antimicrobial activity of two defensins from I. scapularis with emphasis on human pathogenic bacterial strains and important phytopathogenic fungi.

METHODS

Scapularisin-3 and Scapularisin-6 mature peptides were chemically synthesised. In vitro antimicrobial assays were performed to test the activity of these two defensins against species of different bacterial genera including Gram-positive bacteria Staphylococcus aureus, Staphylococcus epidermidis, and Listeria spp. as well as Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa along with two plant-pathogenic fungi from the genus Fusarium. In addition, the tissue-specific expression patterns of Scapularisin-3 and Scapularisin-6 in I. scapularis midgut, salivary glands and embryo-derived cell lines were determined using PCR. Finally, tertiary structures of the two defensins were predicted and structural analyses were conducted.

RESULTS

Scapularisin-6 efficiently killed L. grayi, and both Scapularisin-3 and Scapularisin-6 caused strong inhibition (IC50 value: ~1 μM) of the germination of plant-pathogenic fungi Fusarium culmorum and Fusarium graminearum. Scapularisin-6 gene expression was observed in I. scapularis salivary glands and midgut. However, Scapularisin-3 gene expression was only detected in the salivary glands. Transcripts from the two defensins were not found in the I. scapularis tick cell lines ISE6 and ISE18.

CONCLUSION

Our results have two main implications. Firstly, the anti-Listeria and antifungal activities of Scapularisin-3 and Scapularisin-6 suggest that these peptides may be useful for (i) treatment of antibiotic-resistant L. grayi in humans and (ii) plant protection. Secondly, the antimicrobial properties of the two defensins described in this study may pave the way for further studies regarding pathogen invasion and innate immunity in I. scapularis.

Defensin from the ornate sheep tick Dermacentor marginatus and its effect on Lyme borreliosis spirochetes

Expression of the previously reported defensin of the tick Dermacentor marginatus (defDM) was analysed in different organs by RT-PCR. mRNA of the defDM gene was detected in the hemolymph, midgut and salivary glands. Moreover defDM was isolated from the tick hemolymph using RP-HPLC and its sequence was determined by mass spectrometry and Edman degradation. Synthetic peptide was used for determining biological activities. The results showed an anti-Gram-positive bacterial role for the defensin. As D. marginatus ticks appear not to be vectors of the Lyme disease agent of the complex Borrelia burgdorferi sensu lato, we tested the influence of defDM on Borrelia afzelii. There is a very clear borrelicidal activity of the defensin, which is concentration dependent and suggests a possible role in the clearing of Borrelia ingested by D. marginatus ticks.

Defending the fort: a role for defensin-2 in limiting Rickettsia montanensis infection of Dermacentor variabilis

The importance of tick defensins is evidenced by their expression in a wide variety of tick tissues and prevalence across many tick genera. To date, the functional and biological significance of defensin-2 as a rickettsiastatic or rickettsiacidal antimicrobial peptide has not been addressed. In a previous study, defensin-2 transcription was shown to increase in Dermacentor variabilis ticks challenged with Rickettsia montanensis. In the present study, the hypothesis that defensin-2 is functional as a rickettsiastatic and/or rickettsiacidal antimicrobial peptide is tested. We show that defensin-2 plays a role in reducing burden after acquisition of Rickettsia montanensis through capillary feeding. Moreover, defensin-2 is shown to associate with R. montanensis in vitro and in vivo, causing cytoplasmic leakiness.

Identification and partial characterisation of new members of the Ixodes ricinus defensin family

The hard-bodied tick Ixodes ricinus (castor bean tick) is the most common tick species in Europe. I. ricinus is a vector of the causative agents of diseases that affect humans and animals including tick-borne encephalitis, borreliosis, tick-borne fever and babesiosis. The innate immune system provides ticks with quite an efficient defence against some pathogenic microorganisms in the event of their penetration into the tick body or through the blood meal. Antimicrobial peptides (AMPs) constitute an important feature of the tick immune system. Defensins are a well-known class of AMPs. Members of the defensin family of proteins have been reported in several tick species. So far, only two defensins had been identified from I. ricinus. In this study, we report the identification of six novel putative defensins from I. ricinus at the genomic and transcriptional levels. At the genomic level they show differences with one being intronless, while others contain two introns. The expression pattern of these molecules in the salivary glands, midgut, ovary, Malpighian tubules, haemolymph and the tick cell line IRE/CTVM19 was determined. Some of them are tissue specific while others seem to be ubiquitous. Molecular and phylogenetic analyses show that these novel members of the I. ricinus defensin family differ phylogenetically and structurally; nevertheless, the cysteine pattern is highly conserved among the family members. Finally, antimicrobial-peptide prediction tools were used to predict putative antimicrobial activity of our defensins. They show putative antimicrobial activity mainly against Gram-positive bacteria. This study displays the diversity of the defensin family in the tick I. ricinus.

Helminth Allergens, Parasite-Specific IgE, and Its Protective Role in Human Immunity

The Th2 immune response, culminating in eosinophilia and IgE production, is not only characteristic of allergy but also of infection by parasitic worms (helminths). Anti-parasite IgE has been associated with immunity against a range of helminth infections and many believe that IgE and its receptors evolved to help counter metazoan parasites. Allergens (IgE-antigens) are present in only a small minority of protein families and known IgE targets in helminths belong to these same families (e.g., EF-hand proteins, tropomyosin, and PR-1 proteins). During some helminth infection, especially with the well adapted hookworm, the Th2 response is moderated by parasite-expressed molecules. This has been associated with reduced allergy in helminth endemic areas and worm infection or products have been proposed as treatments for allergic conditions. However, some infections (especially Ascaris) are associated with increased allergy and this has been linked to cross-reactivity between worm proteins (e.g., tropomyosins) and highly similar molecules in dust-mites and insects. The overlap between allergy and helminth infection is best illustrated in Anisakis simplex, a nematode that when consumed in under-cooked fish can be both an infective helminth and a food allergen. Nearly 20 molecular allergens have been isolated from this species, including tropomyosin (Ani s 3) and the EF-hand protein, Ani s troponin. In this review, we highlight aspects of the biology and biochemistry of helminths that may have influenced the evolution of the IgE response. We compare dominant IgE-antigens in worms with clinically important environmental allergens and suggest that arrays of such molecules will provide important information on anti-worm immunity as well as allergy.

Interaction of the tick immune system with transmitted pathogens

Ticks are hematophagous arachnids transmitting a wide variety of pathogens including viruses, bacteria, and protozoans to their vertebrate hosts. The tick vector competence has to be intimately linked to the ability of transmitted pathogens to evade tick defense mechanisms encountered on their route through the tick body comprising midgut, hemolymph, salivary glands or ovaries. Tick innate immunity is, like in other invertebrates, based on an orchestrated action of humoral and cellular immune responses. The direct antimicrobial defense in ticks is accomplished by a variety of small molecules such as defensins, lysozymes or by tick-specific antimicrobial compounds such as microplusin/hebraein or 5.3-kDa family proteins. Phagocytosis of the invading microbes by tick hemocytes is likely mediated by the primordial complement-like system composed of thioester-containing proteins, fibrinogen-related lectins and convertase-like factors. Moreover, an important role in survival of the ingested microbes seems to be played by host proteins and redox balance maintenance in the tick midgut. Here, we summarize recent knowledge about the major components of tick immune system and focus on their interaction with the relevant tick-transmitted pathogens, represented by spirochetes (Borrelia), rickettsiae (Anaplasma), and protozoans (Babesia). Availability of the tick genomic database and feasibility of functional genomics based on RNA interference greatly contribute to the understanding of molecular and cellular interplay at the tick-pathogen interface and may provide new targets for blocking the transmission of tick pathogens.

Structural and functional characterization of peptides derived from the carboxy-terminal region of a defensin from the tick Ornithodoros savignyi

Tick defensins may serve as templates for the development of multifunctional peptides. The purpose of this study was to evaluate shorter peptides derived from tick defensin isoform 2 (OsDef2) in terms of their antibacterial, antioxidant, and cytotoxic activities. We compared the structural and functional properties of a synthetic peptide derived from the carboxy-terminal of the parent peptide (Os) to that of an analogue in which the three cysteine residues were omitted (Os-C). Here, we report that both peptides were bactericidal (MBC values ranging from 0.94-15 µg/ml) to both Gram-positive and Gram-negative bacteria, whereas the parent peptide only exhibited Gram-positive antibacterial activity. The Os peptide was found to be two-fold more active than Os-C against three of the four tested bacteria but equally active against Staphylococcus aureus. Os showed rapid killing kinetics against both Escherichia coli and Bacillus subtilis, whereas Os-C took longer, suggesting different modes of action. Scanning electron microscopy showed that in contrast to melittin for which blebbing of bacterial surfaces was observed, cells exposed to either peptide appeared flattened and empty. Circular dichroism data indicated that in a membrane-mimicking environment, the cysteine-containing peptide has a higher α-helical content. Both peptides were found to be non-toxic to mammalian cells. Moreover, the peptides displayed potent antioxidant activity and were 12 times more active than melittin. Multifunctional peptides hold potential for a wide range of clinical applications and further investigation into their mode of antibacterial and antioxidant properties is therefore warranted.

Inhibitory effect of cyclophilin A from the hard tick Haemaphysalis longicornis on the growth of Babesia bovis and Babesia bigemina

Haemaphysalis longicornis is known as one of the most important ticks transmitting Babesia parasites in East Asian countries, including Babesia ovata and Babesia gibsoni, as well as Theileria parasites. H. longicornis is not the natural vector of Babesia bovis and Babesia bigemina. Vector ticks and transmitted parasites are thought to have established unique host-parasite interaction for their survival, meaning that vector ticks may have defensive molecules for the growth control of parasites in their bodies. However, the precise adaptation mechanism of tick-Babesia parasites is still unknown. Recently, cyclophilin A (CyPA) was reported to be important for the development of Babesia parasites in ticks. To reveal a part of their adaptation mechanism, the current study was conducted. An injection of B. bovis-infected RBCs into adult female H. longicornis ticks was found to upregulate the expression profiles of the gene and protein of CyPA in H. longicornis (HlCyPA). In addition, recombinant HlCyPA (rHlCyPA) purified from Escherichia coli exhibited significant inhibitory growth effects on B. bovis and B. bigemina cultivated in vitro, without any hemolytic effect on bovine RBCs at all concentrations used. In conclusion, our results suggest that HlCyPA might play an important role in the growth regulation of Babesia parasites in H. longicornis ticks, during natural acquisition from an infected host. Furthermore, rHlCyPA may be a potential alternative chemotherapeutic agent against babesiosis.

Cloning and characterization of a male-specific defensin-like antimicrobial peptide from the tick Haemaphysalis longicornis

A novel gene was identified from a cDNA library of the male accessory glands of Haemaphysalis longicornis. The full-length cDNA of the gene was 349bp, encoding a 79-amino acid defensin-like protein and therefore the protein was named HlMS-defensin. Reverse transcriptase-PCR results suggested that this gene was expressed exclusively in male ticks. The tissue expression pattern and the mRNA levels of HlMS-defensin during blood feeding were determined using real-time PCR. HlMS-defensin was expressed predominately in the male accessory gland and was up-regulated during blood feeding. The antimicrobial activity of a synthetic peptide based on the predicted mature portion of HlMS-defensin was examined against a variety of Gram-positive and Gram-negative bacteria and fungi. It appears that ticks use the antimicrobial peptide to protect their reproductive tracts from microbial infections. The protective role of HlMS-defensin during mating was also discussed.

Impact of climate trends on tick-borne pathogen transmission

Recent advances in climate research together with a better understanding of tick-pathogen interactions, the distribution of ticks and the diagnosis of tick-borne pathogens raise questions about the impact of environmental factors on tick abundance and spread and the prevalence and transmission of tick-borne pathogens. While undoubtedly climate plays a role in the changes in distribution and seasonal abundance of ticks, it is always difficult to disentangle factors impacting on the abundance of tick hosts from those exerted by human habits. All together, climate, host abundance, and social factors may explain the upsurge of epidemics transmitted by ticks to humans. Herein we focused on tick-borne pathogens that affect humans with epidemic potential. Borrelia burgdorferi s.l. (Lyme disease), Anaplasma phagocytophilum (human granulocytic anaplasmosis), and tick-borne encephalitis virus (tick-borne encephalitis) are transmitted by Ixodes spp. Crimean-Congo hemorrhagic fever virus (Crimean-Congo hemorrhagic fever) is transmitted by Hyalomma spp. In this review, we discussed how vector tick species occupy the habitat as a function of different climatic factors, and how these factors impact on tick survival and seasonality. How molecular events at the tick-pathogen interface impact on pathogen transmission is also discussed. Results from statistically and biologically derived models are compared to show that while statistical models are able to outline basic information about tick distributions, biologically derived models are necessary to evaluate pathogen transmission rates and understand the effect of climatic variables and host abundance patterns on pathogen transmission. The results of these studies could be used to build early alert systems able to identify the main factors driving the subtle changes in tick distribution and seasonality and the prevalence of tick-borne pathogens.

Parasiticidal activity of Haemaphysalis longicornis longicin P4 peptide against Toxoplasma gondii

The Haemaphysalis longicornis longicin P4 peptide is an active part peptide produced by longicin which displays bactericidal activity against both Gram-negative and Gram-positive bacteria and other microorganisms. In the present study, the effect of the longicin P4 peptide on the infectivity of Toxoplasma gondii parasites was examined in vitro. Tachyzoites of T. gondii incubated with longicin P4 had induced aggregation and lost the trypan blue dye exclusion activity and the invasion ability into the mouse embryonal cell line (NIH/3T3). Longicin P4 bound to T. gondii tachyzoites, as demonstrated by fluoresce microscopic analysis. An electron microscopic analysis and a fluorescence propidium iodide exclusion assay of tachyzoites exposed to longicin P4 revealed pore formation in the cellular membrane, membrane disorganization, and hollowing as well as cytoplasmic vacuolization. The number of tachyzoites proliferated in mouse macrophage cell line (J774A.1) was significantly decreased by incubation with longicin P4. These findings suggested that longicin P4 conceivably impaired parasite membranes, leading to the destruction of Toxoplasma parasites in J774A.1 cells. Thus, longicin P4 is an interesting candidate for antitoxoplasmosis drug design that causes severe toxicity to T. gondii and plays an important role in reducing cellular infection. This is the first report showing that longicin P4 causes aggregation and membrane injury of parasites, leading to Toxoplasma tachyzoite destruction.

Functional genomics studies of Rhipicephalus (Boophilus) annulatus ticks in response to infection with the cattle protozoan parasite, Babesia bigemina

Ticks are obligate haematophagous ectoparasites of wild and domestic animals as well as humans, considered to be second worldwide to mosquitoes as vectors of human diseases, but the most important vectors of disease-causing pathogens in domestic and wild animals. Babesia spp. are tick-borne pathogens that cause a disease called babesiosis in a wide range of animals and in humans. In particular, Babesia bovis and Babesia bigemina are transmitted by cattle ticks, Rhipicephalus (Boophilus) annulatus and Rhipicephalus microplus, which are considered the most important cattle ectoparasites with major economic impacts on cattle production. The objectives of this study were to identify R. annulatus genes differentially expressed in response to infection with B. bigemina. Functional analyses were conducted on selected genes by RNA interference in both R. annulatus and R. microplus ticks. Eight hundred randomly selected suppression-subtractive hybridisation library clones were sequenced and analysed. Molecular function Gene Ontology assignments showed that the obtained tick sequences encoded for proteins with different cellular functions. Differentially expressed genes with putative functions in tick-pathogen interactions were selected for validation of SSH results by real-time reverse transcription-PCR. Genes encoding for TROSPA, calreticulin, ricinusin and serum amyloid A were over-expressed in B. bigemina-infected ticks while Kunitz-type protease inhibitor 5 mRNA levels were down-regulated in infected ticks. Functional analysis of differentially expressed genes by double stranded RNA-mediated RNAi showed that under the conditions of the present study knockdown of TROSPA and serum amyloid A significantly reduced B. bigemina infection levels in R. annulatus while in R. microplus, knockdown of TROSPA, serum amyloid A and calreticulin also reduced pathogen infection levels when compared with controls. Several studies have characterised the tick-pathogen interface at the molecular level. However, to our knowledge this is the first report of functional genomics studies in R. annulatus infected with B. bigemina. The results reported here increase our understanding of the role of tick genes in Babesia infection/multiplication.

Functional characterization of two defensin isoforms of the hard tick Ixodes ricinus

BACKGROUND

The immune system of ticks is stimulated to produce many pharmacologically active molecules during feeding and especially during pathogen invasion. The family of cationic peptides - defensins - represents a specific group of antimicrobial compounds with six conserved cysteine residues in a molecule.

RESULTS

Two isoforms of the defensin gene (def1 and def2) were identified in the European tick Ixodes ricinus. Expression of both genes was induced in different tick organs by a blood feeding or pathogen injection. We have tested the ability of synthetic peptides def1 and def2 to inhibit the growth or directly kill several pathogens. The antimicrobial activities (expressed as minimal inhibition concentration and minimal bactericidal concentration values) against Gram positive bacteria were confirmed, while Gram negative bacteria, yeast, Tick Borne Encephalitis and West Nile Viruses were shown to be insensitive. In addition to antimicrobial activities, the hemolysis effect of def1 and def2 on human erythrocytes was also established.

CONCLUSIONS

Although there is nothing known about the realistic concentration of defensins in I. ricinus tick body, these results suggest that defensins play an important role in defence against different pathogens. Moreover this is a first report of a one amino acid substitution in a defensins molecule and its impact on antimicrobial activity.

Identification of a cysteine-rich antimicrobial peptide from salivary glands of the tick Rhipicephalus haemaphysaloides

The presence of an effective immune response in the hemocoel of ticks is crucial for survival, as it prevents the invasion of pathogens throughout the animal's body. Antimicrobial peptides (AMPs) play an important role in this response by rapidly killing invading microorganisms. In this study, a subtraction hybridization cDNA library was constructed from the salivary glands of the unfed and fed female tick Rhipicephalus haemaphysaloides, and a novel cysteine-rich AMP designated Rhamp (R. haemaphysaloides antimicrobial peptide) was isolated and identified. The Rhamp was encoded by a gene with an open reading frame of 303 bp which encoded a mature peptide with 8 kDa molecular weight. No identity was found by BLAST search to any database entries. The sequence encoding the Rhamp was subcloned into the pGEX-4T vector and expressed in Escherichia coli. The recombinant protein of Rhamp showed chymotrypsin and elastase-inhibitory activity and markedly inhibited the growth of gram-negative bacteria, including Pseudomonas aeruginosa, Salmonella typhimurium, and E. coli. Moreover, the recombinant protein also exerted low hemolytic activity. These results indicate the Rhamp is a novel antimicrobial peptide with proteinase activity from the tick R. haemaphysaloides.

A novel defensin-like peptide from salivary glands of the hard tick, Haemaphysalis longicornis

A novel defensin-like antimicrobial peptide named longicornsin was isolated from the salivary glands of the hard tick, Haemaphysalis longicornis, using a 10-kDa cut-off Centriprep filter and reversed-phase high-performance liquid chromatography (RP-HPLC). Its amino acid sequence was determined as DFGCGQGMIFMCQRRCMRLYPGSTGFCRGFRCMCDTHIPLRPPFMVG by Edman degradation. The cDNA encoding longicornsin was cloned by cDNA library screening. The predicted protein from the cDNA sequence was composed of 78 amino acids including a mature longicornsin. It showed similarity with defensin-like peptides from other ticks by BLAST search. Different from most other tick defensin-like peptides, longicornsin had a C-terminal extension. Purified longicornsin exerted potent antimicrobial activities against bacteria and fungi. Interestingly, it even showed strong antimicrobial ability against drug-resistant microorganisms and Helicobacter pylori. The results of this study indicated that longicornsin is a potential candidate for novel antimicrobial drug design.