Rhipicephalus (Boophilus) microplus: clotting time in tick-infested skin varies according to local inflammation and gene expression patterns in tick salivary glands

Genetic factors underlying host resistance to Rhipicephalus microplus tick infestation in Braford cattle: a systems biology perspective

Approximately 80% of the world's cattle are raised in regions with a high risk of tick-borne diseases, resulting in significant economic losses due to parasitism by Rhipicephalus (Boophilus) microplus. However, the lack of a systemic biology approach hampers a comprehensive understanding of tick-host interactions that mediate tick resistance phenotypes. Here, we conducted a genome-wide association study (GWAS) of 2933 Braford cattle and found 340 single-nucleotide polymorphisms (SNPs) associated with tick counts. Gene expression analyses were performed on skin samples obtained from previously tick-exposed heifers with extremely high or low estimated breeding values for R. microplus counts. Evaluations were performed both before and after artificial infestation with ticks. Differentially expressed genes were found within 1-Mb windows centered at significant SNPs from GWAS. A total of 330 genes were related to the breakdown of homeostasis that was induced by larval attachment to bovine skin. Enrichment analysis pointed to a key role of proteolysis and signal transduction via JAK/STAT, NFKB and WNT/beta catenin signaling pathways. Integrative analysis on matrixEQTL revealed two cis-eQTLs and four significant SNPs in the genes peptidyl arginine deiminase type IV (PADI4) and LOC11449251. The integration of genomic data from QTL maps and transcriptome analyses has identified a set of twelve key genes that show significant associations with tick loads. These genes could be key candidates to improve the accuracy of genomic predictions for tick resistance in Braford cattle.

Interaction between a Sulfated Polysaccharide from Sea Cucumber and Gut Microbiota Influences the Fat Metabolism in Rats

Due to its significant physiological effects, a sulfated polysaccharide has been considered an important nutrient of sea cucumber, but its metabolism in vivo is still unclear. The present study investigated the metabolism of a sea cucumber sulfated polysaccharide (SCSP) in rats and its influence on the metabolite profiles. The quantification by HPLC-MS/MS revealed that the blood level of SCSP achieved a maximum of 54.0 ± 4.8 μg/mL at 2 h after gavage, almost no SCSP was excreted through urine, and 55.4 ± 29.8% of SCSP was eliminated through feces within 24 h. These results prove the utilization of SCSP by gut microbiota, and a further microbiota sequencing analysis indicated that the SCSP utilization in the gut was positively correlated with Muribaculaceae and Clostridia_UCG-014. In addition, the non-targeted metabolomic analysis demonstrated the significant effects of SCSP administration on the metabolite profiles of blood, urine, and feces. It is worth noting that the SCSP supplement decreased palmitic acid, stearic acid, and oleic acid in blood and urine while increasing stearic acid, linoleic acid, and γ-linolenic acid in feces, suggesting the inhibition of fat absorption and the enhancement of fat excretion by SCSP, respectively. The present study shed light on the metabolism in vivo and the influence on the fat metabolism of SCSP.

Phosphoproteomic Analysis of Haemaphysalis longicornis Saliva Reveals the Influential Contributions of Phosphoproteins to Blood-Feeding Success

Tick saliva, an essential chemical secretion of the tick salivary gland, is indispensable for tick survival owing to the physiological influence it exerts on the host defence mechanisms via the instrumentality of its cocktail of pharmacologically active molecules (proteins and peptides). Much research about tick salivary proteome has been performed, but how most of the individual salivary proteins are utilized by ticks to facilitate blood acquisition and pathogen transmission is not yet fully understood. In addition, the phosphorylation of some proteins plays a decisive role in their function. However, due to the low phosphorylation level of protein, especially for a small amount of protein, it is more difficult to study phosphorylation. Maybe, for this reason, the scarcity of works on the phosphorylated tick salivary proteomes still abound. Here, we performed a phosphoproteomic analysis of Haemaphysalis longicornis tick saliva via TiO₂ enrichment and the most advanced Thermo Fisher Orbitrap Exploris 480 mass spectrometer for identification. A total of 262 phosphorylated tick saliva proteins were identified and were subjected to functional annotation/enrichment analysis. Cellular and metabolic process terms accounted for the largest proportion of the saliva proteins, with the participation of these proteins in vital intracellular and extracellular transport-oriented processes such as vesicle-mediated transport, exocytic process, cell adhesion, and movement of cell/subcellular component. “Endocytosis”, “Protein processing in endoplasmic reticulum”, and “Purine metabolism” were the most significantly enriched pathways. The knockdown (RNAi) of Tudor domain-containing protein (TCP), actin-depolymerizing factors (ADF), programmed cell death protein (PD), and serine/threonine-protein kinase (SPK) resulted in the dissociation of collagen fibers and the pilosebaceous unit, increased inflammatory infiltrates/granulocytes (possibly heterophiles), and the depletion of the epithelium. Ticks injected with SPK dsRNA engorged normally but with a change in skin colour (possibly an autoimmune reaction) and the failure to produce eggs pointing to a possible role of SPK in reproduction and host immune modulation. Ticks injected with ADF dsRNA failed to acquire blood, underscoring the role of ADF in facilitating tick feeding. The results of this study showed the presence of phosphorylation in tick saliva and highlight the roles of salivary phosphoproteins in facilitating tick feeding.

Serum proteomes of Santa Gertrudis cattle before and after infestation with Rhipicephalus australis ticks

Previous studies have applied genomics and transcriptomics to identify immune and genetic markers as key indicator traits for cattle tick susceptibility/resistance; however, results differed between breeds, and there is lack of information on the use of host proteomics. Serum samples from Santa Gertrudis cattle (naïve and phenotyped over 105 days as tick-resistant [TR] or tick-susceptible [TS]) were used to conduct differential abundance analyses of protein profiles. Serum proteins were digested into peptides followed by identification and quantification using sequential window acquisition of all instances of theoretical fragment ion mass spectrometry. Before tick infestation, abundance of 28 proteins differed significantly (adjusted P < 10^-5 ) between TR and TS. These differences were also observed following tick infestation (TR vs TS) with a further eight differentially abundant proteins in TR cattle, suggesting possible roles in adaptive responses. The intragroup comparisons (TS-0 vs TS and TR-0 vs TR) showed that tick infestation elicited quite similar responses in both groups of cattle, but with relatively stronger responses in TR cattle. Many of the significantly differentially abundant proteins in TR Santa Gertrudis cattle (before and after tick infestation) were associated with immune responses including complement factors, chemotaxis for immune cells and acute-phase responses.

Towards a new phenotype for tick resistance in beef and dairy cattle: a review

About 80% of the world’s cattle are affected by ticks and tick-borne diseases, both of which cause significant production losses. Cattle host resistance to ticks is the most important factor affecting the economics of tick control, but it is largely neglected in tick-control programs due to technical difficulties and costs associated with identifying individual-animal variation in resistance. The present paper reviews the scientific literature to identify factors affecting resistance of cattle to ticks and the biological mechanisms of host tick resistance, to develop alternative phenotype(s) for tick resistance. If new cost-effective phenotype(s) can be developed and validated, then tick resistance of cattle could be genetically improved using genomic selection, and incorporated into breeding objectives to simultaneously improve cattle productive attributes and tick resistance. The phenotype(s) could also be used to improve tick control by using cattle management. On the basis of the present review, it is recommended that three possible phenotypes (haemolytic analysis; measures of skin hypersensitivity reactions; simplified artificial tick infestations) be further developed to determine their practical feasibility for consistently, cost-effectively and reliably measuring cattle tick resistance in thousands of individual animals in commercial and smallholder farmer herds in tropical and subtropical areas globally. During evaluation of these potential new phenotypes, additional measurements should be included to determine the possibility of developing a volatile-based resistance phenotype, to simultaneously improve cattle resistance to both ticks and biting flies. Because the current measurements of volatile chemistry do not satisfy the requirements of a simple, cost-effective phenotype for use in commercial cattle herds, consideration should also be given to inclusion of potentially simpler measures to enable indirect genetic selection for volatile-based resistance to ticks.

Host-specific expression of Ixodes scapularis salivary genes

Ixodes scapularis vectors several pathogens including Borrelia burgdorferi, the agent of Lyme disease. Nymphal and larval stages, and the pathogens transmitted by I. scapularis are maintained in a zoonotic cycle involving rodent reservoir hosts, predominantly Peromyscus leucopus. Humans are not reservoir hosts, however, accidental encounters of infected ticks with humans, results in pathogen transmission to the human host. Laboratory models of non-reservoir hosts such as guinea pigs develop a strong immune response to tick salivary proteins and reject ticks upon repeated tick infestations. Anecdotal and scientific evidence suggests that humans that get frequent tick bites might also develop resistance to ticks. Mus musculus, the laboratory model of natural host, does not develop resistance to I. scapularis upon repeated tick infestations. Addressing this dichotomy in vector-host interaction, we present data that suggest that the salivary transcriptome and proteome composition is different in mouse and guinea pig-fed I. scapularis, and that these differences might contribute to differences in host immune responses. These findings reveal a new insight into vector-host interactions and offer a functional paradigm to better understand the phenomenon of acquired tick-resistance.

Non-infectious illness after tick bite

Tick bites are common and may have non-infectious complications. Reactions range from local reactions to systemic syndromes, tick paralysis, mammalian meat allergy and tick anaphylaxis. Management revolves around prevention with vector avoidance and immediate removal of the tick if bitten. Treatment of bite reactions is usually symptomatic only with anti-histamines or corticosteroids. Adrenaline may be indicated for severe cases.

Cattle Tick Rhipicephalus microplus-Host Interface: A Review of Resistant and Susceptible Host Responses

Ticks are able to transmit tick-borne infectious agents to vertebrate hosts which cause major constraints to public and livestock health. The costs associated with mortality, relapse, treatments, and decreased production yields are economically significant. Ticks adapted to a hematophagous existence after the vertebrate hemostatic system evolved into a multi-layered defense system against foreign invasion (pathogens and ectoparasites), blood loss, and immune responses. Subsequently, ticks evolved by developing an ability to suppress the vertebrate host immune system with a devastating impact particularly for exotic and crossbred cattle. Host genetics defines the immune responsiveness against ticks and tick-borne pathogens. To gain an insight into the naturally acquired resistant and susceptible cattle breed against ticks, studies have been conducted comparing the incidence of tick infestation on bovine hosts from divergent genetic backgrounds. It is well-documented that purebred and crossbred Bos taurus indicus cattle are more resistant to ticks and tick-borne pathogens compared to purebred European Bos taurus taurus cattle. Genetic studies identifying Quantitative Trait Loci markers using microsatellites and SNPs have been inconsistent with very low percentages relating phenotypic variation with tick infestation. Several skin gene expression and immunological studies have been undertaken using different breeds, different samples (peripheral blood, skin with tick feeding), infestation protocols and geographic environments. Susceptible breeds were commonly found to be associated with the increased expression of toll like receptors, MHC Class II, calcium binding proteins, and complement factors with an increased presence of neutrophils in the skin following tick feeding. Resistant breeds had higher levels of T cells present in the skin prior to tick infestation and thus seem to respond to ticks more efficiently. The skin of resistant breeds also contained higher numbers of eosinophils, mast cells and basophils with up-regulated proteases, cathepsins, keratins, collagens and extracellular matrix proteins in response to feeding ticks. Here we review immunological and molecular determinants that explore the cattle tick Rhipicephalus microplus-host resistance phenomenon as well as contemplating new insights and future directions to study tick resistance and susceptibility, in order to facilitate interventions for tick control.

Mining a differential sialotranscriptome of Rhipicephalus microplus guides antigen discovery to formulate a vaccine that reduces tick infestations

BACKGROUND

Ticks cause massive damage to livestock and vaccines are one sustainable substitute for the acaricides currently heavily used to control infestations. To guide antigen discovery for a vaccine that targets the gamut of parasitic strategies mediated by tick saliva and enables immunological memory, we exploited a transcriptome constructed from salivary glands from all stages of Rhipicephalus microplus ticks feeding on genetically tick-resistant and susceptible bovines.

RESULTS

Different levels of host anti-tick immunity affected gene expression in tick salivary glands; we thus selected four proteins encoded by genes weakly expressed in ticks attempting to feed on resistant hosts or otherwise abundantly expressed in ticks fed on susceptible hosts; these sialoproteins mediate four functions of parasitism deployed by male ticks and that do not induce antibodies in naturally infected, susceptible bovines. We then evaluated in tick-susceptible heifers an alum-adjuvanted vaccine formulated with recombinant proteins. Parasite performance (i.e. weight and numbers of females finishing their parasitic cycle) and titres of antigen-specific antibodies were significantly reduced or increased, respectively, in vaccinated versus control heifers, conferring an efficacy of 73.2%; two of the antigens were strong immunogens, rich in predicted T-cell epitopes and challenge infestations boosted antibody responses against them.

CONCLUSION

Mining sialotranscriptomes guided by the immunity of tick-resistant hosts selected important targets and infestations boosted immune memory against salivary antigens.

Immune and biochemical responses in skin differ between bovine hosts genetically susceptible and resistant to the cattle tick Rhipicephalus microplus

Background

Ticks attach to and penetrate their hosts’ skin and inactivate multiple components of host responses in order to acquire a blood meal. Infestation loads with the cattle tick, Rhipicephalus microplus, are heritable: some breeds carry high loads of reproductively successful ticks, whereas in others, few ticks feed and reproduce efficiently.

Methods

In order to elucidate the mechanisms that result in the different outcomes of infestations with cattle ticks, we examined global gene expression and inflammation induced by tick bites in skins from one resistant and one susceptible breed of cattle that underwent primary infestations with larvae and nymphs of R. microplus. We also examined the expression profiles of genes encoding secreted tick proteins that mediate parasitism in larvae and nymphs feeding on these breeds.

Results

Functional analyses of differentially expressed genes in the skin suggest that allergic contact-like dermatitis develops with ensuing production of IL-6, CXCL-8 and CCL-2 and is sustained by HMGB1, ISG15 and PKR, leading to expression of pro-inflammatory chemokines and cytokines that recruit granulocytes and T lymphocytes. Importantly, this response is delayed in susceptible hosts. Histopathological analyses of infested skins showed inflammatory reactions surrounding tick cement cones that enable attachment in both breeds, but in genetically tick-resistant bovines they destabilized the cone. The transcription data provided insights into tick-mediated activation of basophils, which have previously been shown to be a key to host resistance in model systems. Skin from tick-susceptible bovines expressed more transcripts encoding enzymes that detoxify tissues. Interestingly, these enzymes also produce volatile odoriferous compounds and, accordingly, skin rubbings from tick-susceptible bovines attracted significantly more tick larvae than rubbings from resistant hosts. Moreover, transcripts encoding secreted modulatory molecules by the tick were significantly more abundant in larval and in nymphal salivary glands from ticks feeding on susceptible bovines.

Conclusions

Compared with tick-susceptible hosts, genes encoding enzymes producing volatile compounds exhibit significantly lower expression in resistant hosts, which may render them less attractive to larvae; resistant hosts expose ticks to an earlier inflammatory response, which in ticks is associated with significantly lower expression of genes encoding salivary proteins that suppress host immunity, inflammation and coagulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1945-z) contains supplementary material, which is available to authorized users.

The putative role of Rhipicephalus microplus salivary serpins in the tick-host relationship

Inflammation and hemostasis are part of the host's first line of defense to tick feeding. These systems are in part serine protease mediated and are tightly controlled by their endogenous inhibitors, in the serpin superfamily (serine protease inhibitors). From this perspective ticks are thought to use serpins to evade host defenses during feeding. The cattle tick Rhipicephalus microplus encodes at least 24 serpins, of which RmS-3, RmS-6, and RmS-17 were previously identified in saliva of this tick. In this study, we screened inhibitor functions of these three saliva serpins against a panel of 16 proteases across the mammalian defense pathway. Our data confirm that Pichia pastoris-expressed rRmS-3, rRmS-6, and rRmS-17 are likely inhibitors of pro-inflammatory and pro-coagulant proteases. We show that rRmS-3 inhibited chymotrypsin and cathepsin G with stoichiometry of inhibition (SI) indices of 1.8 and 2.0, and pancreatic elastase with SI higher than 10. Likewise, rRmS-6 inhibited trypsin with SI of 2.6, chymotrypsin, factor Xa, factor XIa, and plasmin with SI higher than 10, while rRmS-17 inhibited trypsin, cathepsin G, chymotrypsin, plasmin, and factor XIa with SI of 1.6, 2.6, 2.7, 3.4, and 9.0, respectively. Additionally, we observed the formation of irreversible complexes between rRmS-3 and chymotrypsin, rRmS-6/rRmS-17 and trypsin, and rRmS-3/rRmS-17 and cathepsin G, which is consistent with typical mechanism of inhibitory serpins. In blood clotting assays, rRmS-17 delayed plasma clotting by 60 s in recalcification time assay, while rRmS-3 and rRmS-6 did not have any effect. Consistent with inhibitor function profiling data, 2.0 μM rRmS-3 and rRmS-17 inhibited cathepsin G-activated platelet aggregation in a dose-responsive manner by up to 96% and 95% respectively. Of significant interest, polyclonal antibodies blocked inhibitory functions of the three serpins. Also notable, antibodies to Amblyomma americanum, Ixodes scapularis, and Rhipicephalus sanguineus tick saliva proteins cross-reacted with the three R. microplus saliva serpins, suggesting the potential of these proteins as candidates for universal anti-tick vaccines.

Modulation of host immunity by tick saliva

Next generation sequencing and proteomics have helped to comprehensively characterize gene expression in tick salivary glands at both the transcriptome and the proteome level. Functional data are, however, lacking. Given that tick salivary secretions are critical to the success of the tick transmission lifecycle and, as a consequence, for host colonization by the pathogens they spread, we thoroughly review here the literature on the known interactions between tick saliva (or tick salivary gland extracts) and the innate and adaptive vertebrate immune system. The information is intended to serve as a reference for functional characterization of the numerous genes and proteins expressed in tick salivary glands with an ultimate goal to develop novel vector and pathogen control strategies.

SIGNIFICANCE

We overview all the known interactions of tick saliva with the vertebrate immune system. The provided information is important, given the recent developments in high-throughput transcriptomic and proteomic analysis of gene expression in tick salivary glands, since it may serve as a guideline for the functional characterization of the numerous newly-discovered genes expressed in tick salivary glands.

Application of M13 phage display for identifying immunogenic proteins from tick (Ixodes scapularis) saliva

Background

Ticks act as vectors for a large number of different pathogens, perhaps most notably Borrelia burgdorferi, the causative agent of Lyme disease. The most prominent tick vector in the United States is the blacklegged tick, Ixodes scapularis. Tick bites are of special public health concern since there are no vaccines available against most tick-transmitted pathogens. Based on the observation that certain non-natural host animals such as guinea pigs or humans can develop adaptive immune responses to tick bites, anti-tick vaccination is a potential approach to tackle health risks associated with tick bites.

Results

The aim of this study was to use an oligopeptide phage display strategy to identify immunogenic salivary gland proteins from I. scapularis that are recognized by human immune sera. Oligopeptide libraries were generated from salivary gland mRNA of 18 h fed nymphal I. scapularis. Eight immunogenic oligopeptides were selected using human immune sera. Three selected immunogenic oligopeptides were cloned and produced as recombinant proteins. The immunogenic character of an identified metalloprotease (MP1) was validated with human sera. This enzyme has been described previously and was hypothesized as immunogenic which was confirmed in this study. Interestingly, it also has close homologs in other Ixodes species.

Conclusion

An immunogenic protein of I. scapularis was identified by oligopeptide phage display. MP1 is a potential candidate for vaccine development.

Influence of pH control in the formation of inclusion bodies during production of recombinant sphingomyelinase-D in Escherichia coli

BACKGROUND

Inclusion bodies (IBs) are aggregated proteins that form clusters when protein is overexpressed in heterologous expression systems. IBs have been considered as non-usable proteins, but recently they are being used as functional materials, catalytic particles, drug delivery agents, immunogenic structures, and as a raw material in recombinant therapeutic protein purification. However, few studies have been made to understand how culture conditions affect the protein aggregation and the physicochemical characteristics that lead them to cluster. The objective of our research was to understand how pH affects the physicochemical properties of IBs formed by the recombinant sphingomyelinase-D of tick expressed in E. coli BL21-Gold (DE3) by evaluating two pH culture strategies.

RESULTS

Uncontrolled pH culture conditions favored recombinant sphingomyelinase-D aggregation and IB formation. The IBs of sphingomyelinase-D produced under controlled pH at 7.5 and after 24 h were smaller (<500 nm) than those produced under uncontrolled pH conditions (>500 nm). Furthermore, the composition, conformation and β-structure formation of the aggregates were different. Under controlled pH conditions in comparison to uncontrolled conditions, the produced IBs presented higher resistance to denaturants and proteinase-K degradation, presented β-structure, but apparently as time passes the IBs become compacted and less sensitive to amyloid dye binding.

CONCLUSIONS

The manipulation of the pH has an impact on IB formation and their physicochemical characteristics. Particularly, uncontrolled pH conditions favored the protein aggregation and sphingomyelinase-D IB formation. The evidence may lead to find methodologies for bioprocesses to obtain biomaterials with particular characteristics, extending the application possibilities of the inclusion bodies.

Microarray analysis of tick-infested skin in resistant and susceptible cattle confirms the role of inflammatory pathways in immune activation and larval rejection

Tick bites promote activation of an inflammatory process that is influenced by bovine genetic composition and its history of previous exposure. Taurine and indicine breeds are known to differ on its immune response development against Rhipicephalus microplus. Nevertheless, further investigation about the complex molecular pathways involved in the development of immune response to tick infestation in cattle presenting the same genetic background is mandatory. The aim of this work was to access the early immune response triggered by R. microplus larvae attachment in previously selected resistant and susceptible animals in a bovine F2 population derived from Gyr (Bos indicus)×Holstein (Bos taurus) crosses. Microarray data analysis of RNA samples from tick infested skin was used to evaluate the gene expression at 0, 24 and 48h after R. microplus larvae attachment. Our experimental design allowed us to deeply explore the immune response related to R. microplus infestation avoiding the innate differences between these breeds. The differentially expressed genes found reveal networks and pathways that suggest a key role of lipid metabolism in inflammation control and impairment of tick infestation in resistant animals. Acute phase response also seems to be impaired in susceptible animals. These results provide new insights about early immune response against ticks and raise the possibility of using immunomodulation processes to improve and develop novel tools for tick control.

Morphological alterations of epidermis of rabbits infested by R. sanguineus ticks and exposed to Selamectin (active principle of Pfizer Revolution(®) acaricide): a confocal microscopy study

The present study analyzed, by means of confocal laser scanning microscopy, the epidermis of rabbits infested by the brown dog tick Rhipicephalus sanguineus and exposed to concentrations of 50%, 80% and 100% of a selamectin-based commercial acaricide (Pfizer's Revolution(®)). The results demonstrated that rabbits exposed to concentrations of 80% and 100% of the Revolution acaricide, which contains 12% selamectin, showed thinning of epithelial tissue of the epidermis with associated cellular disorganization. Individuals exposed to a 50% concentration showed lower epidermal tissue disorganization when compared to those exposed to the higher doses of the acaricide (80% and 100%). Whereas selamectin, when used in higher concentrations (80% and 100% Revolution(®)) can alter the morphology of the epidermis, at lower concentrations (50%), even though still able to eliminate ectoparasites, it causes less toxicity damage to the host. Selamectin can be considered a dose-dependent toxic agent, since higher concentrations increase the morphological changes in the epidermis of the host rabbits.

Proteome of Rhipicephalus sanguineus tick saliva induced by the secretagogues pilocarpine and dopamine

One dimensional gel electrophoresis was used to separate proteins from the saliva of Rhipicephalus sanguineus female ticks fed on rabbits. Gel slices were subjected to tryptic digestion and analyzed by reversed-phase HPLC followed by MS/MS analysis. The data were compared to a database of salivary proteins of the same tick and to the predicted proteins of the host. Saliva was obtained by either pilocarpine or dopamine stimulation of partially fed ticks. Electrophoretic separations of both yielded products that were identified by mass spectrometry, although the pilocarpine-derived sample was of much better quality. The majority of identified proteins were of rabbit origin, indicating the recycling of the host proteins in the tick saliva, including hemoglobin, albumin, haptoglobin, transferring, and a plasma serpin. The few proteins found that were previously associated with parasitism and blood feeding include 2 glycine-rich, cement-like proteins, 2 lipocalins, and a thyropin protease inhibitor. Among other of the 19 tick proteins identified, albeit with undefined roles, were SPARC and cyclophilin A. This catalog provides a resource that can be mined for secreted molecules that play a role in tick-host interactions.

The occurrence of autophagic cell death in the tegument of rabbits pre-infested with Rhipicephalus sanguineus and exposed to selamectin (active principle of acaricide Pfizer Revolution®)

Ticks of Rhipicephalus sanguineus species have great medical and veterinary importance for being a vector of various diseases. In an attempt to minimize their action on the host, people have resorted to chemical control by using various acaricides, such as selamectin. Although previous studies have demonstrated its toxic action in domestic animals, no studies focused on the detection of cell death when exposed to selamectin. For this reason, the technique for detecting autophagic cell death was used in order to demonstrate the responses of rabbits' skin tissues pre-infested with R. sanguineus and exposed to different concentrations of selamectin. The obtained results when exposed to 100 and 80% concentrations of selamectin showed a strong mark of acid phosphatase on the cells of the connective tissue of the dermis and hair follicles, whereas the ones exposed to the 50% concentration had a weak mark on the cells of the connective tissue of the dermis and moderate staining in hair follicles. It became clear that, when used at high concentrations (100 and 80%), selamectin is capable to induce a large scale occurrence of the autophagic cell death process. On the other hand, the concentration of 50% causes minor morphophysiological changes in the skin of rabbit hosts when evaluated the cell death process. Therefore, the data confirms that selamectin is a powerful dose-dependent toxic agent causes increased activity of the enzyme acid phosphatase.

Histopathology of the tegument of rabbits infested by Rhipicephalus sanguineus (ACARI: IXODIDAE) ticks and exposed to selamectin (active principle of acaricide Revolution, Pfizer)

Ticks are hematophagous ectoparasites which can transmit several diseases to the host during their feeding process. When ticks mechanically damage the tissue, they eventually induce inflammatory responses on the skin spot where they are fixed. One of the alternatives to control these ectoparasites is the use of chemical substances like selamectin-the active principle of Pfizer's antiparasitic Revolution-a macrocyclic lactone capable of doing neurotoxic damage to the tick and eventually eliminating infestation in dogs and cats. The purpose of this study was to analyze, using histological and histochemical techniques, the occurrence of morphophysiological alterations in the skin of the host rabbits exposed to selamectin and infested with Rhipicephalus sanguineus (Acari: Ixodidae). Histologically, the exposed and infested rabbits showed a partial and/or total decrease in the stratum corneum and the epithelium decreased in the number of cell layers, consequently reducing the stratification (thinning) and quite pronounced formations of sub-epidermal edemas with consequent disorganization of collagen fibers in the dermal layer's connective tissue. Histochemical tests showed strong periodic acid-Schiff-positive reaction in the hair follicle and some regions of the dermis, besides resynthesis of collagen fibers detected by Mallory's trichrome technique. The obtained results showed that selamectin acts like a toxicant agent when in contact with the skin of the rabbit infested with ticks, inducing morphophysiological alterations in the acute inflammatory process in the animal's tegument. Selamectin is a chemical substance which has a dose-dependent action since higher concentrations cause greater morphophysiological damage in the skin of rabbits.

Immunoregulation of bovine macrophages by factors in the salivary glands of Rhipicephalus microplus

Background

Alternative strategies are required to control the southern cattle tick, Rhipicephalus microplus, due to evolving resistance to commercially available acaricides. This invasive ectoparasite is a vector of economically important diseases of cattle such as bovine babesiosis and anaplasmosis. An understanding of the biological intricacies underlying vector-host-pathogen interactions is required to innovate sustainable tick management strategies that can ultimately mitigate the impact of animal and zoonotic tick-borne diseases. Tick saliva contains molecules evolved to impair host innate and adaptive immune responses, which facilitates blood feeding and pathogen transmission. Antigen presenting cells are central to the development of robust T cell responses including Th1 and Th2 determination. In this study we examined changes in co-stimulatory molecule expression and cytokine response of bovine macrophages exposed to salivary gland extracts (SGE) obtained from 2-3 day fed, pathogen-free adult R. microplus.

Methods

Peripheral blood-derived macrophages were treated for 1 hr with 1, 5, or 10 μg/mL of SGE followed by 1, 6, 24 hr of 1 μg/mL of lipopolysaccharide (LPS). Real-time PCR and cytokine ELISA were used to measure changes in co-stimulatory molecule expression and cytokine response.

Results

Changes were observed in co-stimulatory molecule expression of bovine macrophages in response to R. microplus SGE exposure. After 6 hrs, CD86, but not CD80, was preferentially up-regulated on bovine macrophages when treated with 1 μg/ml SGE and then LPS, but not SGE alone. At 24 hrs CD80, CD86, and CD69 expression was increased with LPS, but was inhibited by the addition of SGE. SGE also inhibited LPS induced upregulation of TNFα, IFNγ and IL-12 cytokines, but did not alter IL-4 or CD40 mRNA expression.

Conclusions

Molecules from the salivary glands of adult R. microplus showed bimodal concentration-, and time-dependent effects on differential up-regulation of CD86 in bovine macrophages activated by the TLR4-ligand, LPS. Up regulation of proinflammatory cytokines and IL-12, a Th1 promoting cytokine, were inhibited in a dose-dependent manner. The co-stimulatory molecules CD80, as well as the cell activation marker, CD69, were also suppressed in macrophages exposed to SGE. Continued investigation of the immunomodulatory factors will provide the knowledge base to research and develop therapeutic or prophylactic interventions targeting R. microplus-cattle interactions at the blood-feeding interface.

Amblyomma americanum (L.) (Acari: Ixodidae) tick salivary gland serine protease inhibitor (serpin) 6 is secreted into tick saliva during tick feeding

In order to successfully feed and transmit disease agents, ticks are thought to inject serine protease inhibitors (serpins) into the host to modulate host defense responses to tick feeding, such as inflammation, the complement activation pathway and blood coagulation. In this study, we show that Amblyomma americanum (Aam) serpin (S) 6 is putatively injected into the host during tick feeding, in that the antibody to recombinant (r) AamS6 specifically reacted with the expected ∼43/45 kDa AamS6 protein band on western blots of pilocarpine-induced tick saliva. Additionally, antibodies to tick saliva proteins that were generated by repeated 48 h infestations of rabbits with adult A. americanum specifically reacted with rAamS6. We speculate that AamS6 is associated with regulating events at the start of the tick feeding process, as temporal and spatial RT-PCR and western blot analyses revealed that both AamS6 mRNA and protein are strongly expressed during the first 24-72 h of feeding time before starting to fade from 96 h. The AamS6 protein has an apparently slow turnover rate in that, although the injection of AamS6 dsRNA into unfed ticks triggered complete disruption of the AamS6 mRNA by the 48 h feeding time point, western blot analysis of protein extracts of the same animals showed that the AamS6 protein that may have been expressed prior to disruption of the AamS6 mRNA was not depleted. We speculate that the presence of the AamS6 protein in ticks despite the complete disruption of the AamS6 mRNA explains the observation that RNAi-mediated silencing of the AamS6 mRNA did not affect the ability of A. americanum ticks to attach onto host skin, successfully feed and lay eggs. These findings are discussed in regards to advances in the molecular biology of ticks.

Molecular genetic approaches for identifying the basis of variation in resistance to tick infestation in cattle

In recent years there has been renewed interest in the adaptation of cattle to challenging environments, largely driven by advances in genomic methods. The current interest in tick resistance is understandable given the major production and welfare implications of tick infestation in tropical and subtropical zones where around 70% of beef cattle are located. Heritability for tick burden in cattle has been shown to range about 0.30, which is sufficient to result in the success of some programs of selection for tick resistance in cattle. Gene-expression studies strongly indicate that both immune and non-immune mechanisms are associated with tick resistance in cattle. Recent quantitative-trait mapping studies have identified chromosome segments and single nucleotide polymorphisms associated with tick burden, but no causal variant has been identified so far. Most of the genetic markers identified for tick burden explain a relatively small proportion of the variance, which is typical of markers for quantitative traits. This leads to the conclusion that panels of multiple markers for tick resistance rather than a single marker will most likely be developed, possibly involving specific panels for zebu or taurine breeds, which could be used for future selection and breeding programs in cattle.