Tick saliva induces regulatory dendritic cells: MAP-kinases and Toll-like receptor-2 expression as potential targets

Genome variation in tick infestation and cryptic divergence in Tunisian indigenous sheep

Background

Ticks are obligate haematophagous ectoparasites considered second to mosquitos as vectors and reservoirs of multiple pathogens of global concern. Individual variation in tick infestation has been reported in indigenous sheep, but its genetic control remains unknown.

Results

Here, we report 397 genome-wide signatures of selection overlapping 991 genes from the analysis, using ROH, LR-GWAS, XP-EHH, and F_ST, of 600 K SNP genotype data from 165 Tunisian sheep showing high and low levels of tick infestations and piroplasm infections. We consider 45 signatures that are detected by consensus results of at least two methods as high-confidence selection regions. These spanned 104 genes which included immune system function genes, solute carriers and chemokine receptor. One region spanned STX5, that has been associated with tick resistance in cattle, implicating it as a prime candidate in sheep. We also observed RAB6B and TF in a high confidence candidate region that has been associated with growth traits suggesting natural selection is enhancing growth and developmental stability under tick challenge. The analysis also revealed fine-scale genome structure indicative of cryptic divergence in Tunisian sheep.

Conclusions

Our findings provide a genomic reference that can enhance the understanding of the genetic architecture of tick resistance and cryptic divergence in indigenous African sheep.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08321-1.

Habitat fragmentation differentially shapes neutral and immune gene variation in a tropical bird species

Habitat fragmentation is a major cause of biodiversity loss, responsible for an alteration of intraspecific patterns of neutral genetic diversity and structure. Although neutral genetic variation can be informative for demographic inferences, it may be a poor predictor of adaptive genetic diversity and thus of the consequences of habitat fragmentation on selective evolutionary processes. In this context, we contrasted patterns of genetic diversity and structure of neutral loci (microsatellites) and immune genes (i.e., toll-like receptors) in an understorey bird species, the wedge-billed woodcreeper Glyphorynchus spirurus. The objectives were (1) to investigate forest fragmentation effects on population genetic diversity, (2) to disentangle the relative role of demography (genetic drift and migration) and selection, and (3) to assess whether immunogenetic patterns could be associated with variation of ectoparasite (i.e., ticks) pressures. Our results revealed an erosion of neutral genetic diversity and a substantial genetic differentiation among fragmented populations, resulting from a decrease in landscape connectivity and leading to the divergence of distinct genetic pools at a small spatial scale. Patterns of genetic diversity observed for TLR4 and TLR5 were concordant with neutral genetic patterns, whereas those observed for TLR3 and TLR21 were discordant. This result underlines that the dominant evolutionary force shaping immunogenetic diversity (genetic drift vs. selection) may be different depending on loci considered. Finally, tick prevalence was higher in fragmented environments. We discussed the hypothesis that pathogen selective pressures may contribute to maintain adaptive genetic diversity despite the negative demographic effect of habitat fragmentation on neutral genetic diversity.

Dendritic Cells as a Disputed Fortress on the Tick-Host Battlefield

From seminal publications in the early 1970s, the world learned that dendritic cells (DCs) are powerful and versatile antigen-presenting cells. It took a few years until the first studies expanded our understanding of the pivotal role of these immune 'soldiers' against ticks. Advances in biochemistry, molecular biology, and bioinformatics have shed light on the identification of key salivary molecules that modulate the biology of DCs in favor of tick parasitism. Here, we present a critical overview of the discoveries accumulated on the tick-host battlefield from a DC perspective. Moreover, the clinical significance of DC-targeted tick salivary components is discussed, not only as facilitators of the transmission of tick-borne pathogens or vaccine candidates, but also as potential immunobiologics to treat immune-mediated diseases.

Association of Salivary Cholinesterase With Arthropod Vectors of Disease

Acetylcholinesterase (AChE) was previously reported to be present in saliva of the southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), with proposed potential functions to 1) reduce acetylcholine toxicity during rapid engorgement, 2) modulate host immune responses, and 3) to influence pathogen transmission and establishment in the host. Potential modulation of host immune responses might include participation in salivary-assisted transmission and establishment of pathogens in the host as has been reported for a number of arthropod vector-borne diseases. If the hypothesis that tick salivary AChE may alter host immune responses is correct, we reasoned that similar cholinesterase activities might be present in saliva of additional arthropod vectors. Here, we report the presence of AChE-like activity in the saliva of southern cattle ticks, Rhipicephalus (Boophilus) microplus; the lone star tick, Amblyomma americanum (Linnaeus); Asian tiger mosquitoes, Aedes albopictus (Skuse); sand flies, Phlebotomus papatasi (Scopoli); and biting midges, Culicoides sonorensis Wirth and Jones. Salivary AChE-like activity was not detected for horn flies Haematobia irritans (L.), stable flies Stomoxys calcitrans (L.), and house flies Musca domestica L. Salivary cholinesterase (ChE) activities of arthropod vectors of disease-causing agents exhibited various Michaelis-Menten KM values that were each lower than the KM value of bovine serum AChE. A lower KM value is indicative of higher affinity for substrate and is consistent with a hypothesized role in localized depletion of host tissue acetylcholine potentially modulating host immune responses at the arthropod bite site that may favor ectoparasite blood-feeding and alter host defensive responses against pathogen transmission and establishment.

Temporal analysis of the bovine lymph node transcriptome during cattle tick (Rhipicephalus microplus) infestation

Livestock production is a fundamental source of revenue and nutrition, wherein cattle-farming constitutes one of the major agricultural industries. Vectors and vector-borne diseases constitute one of the major factors that decrease the livelihood of all farming communities, more so in resource-poor communities and developing countries. Understanding the immunological responses during tick infestation in cattle is instrumental in the development of novel and improved tick control strategies, such as vaccines. In this study, gene expression patterns were compared within the lymph nodes of three cattle breeds at different life stages of the cattle tick, Rhipicephalus microplus. For Bonsmara (5/8Bos taurus indicus × 3/8B. t. taurus) cattle specifically, some 183 genes were found to be differentially expressed within the lymph nodes during larval and adult tick feeding, relative to uninfested cattle. Overall, the data provides evidence for a transcriptional regulatory network that is activated during immature tick infestation, but is down-regulated towards basal transcriptional levels when adult ticks are feeding. Specific processes in the lymph nodes of Bonsmara cattle were found to be differentially regulated on a transcriptional level. These include: (1) Leukocyte recruitment to the lymph node via chemokines and chemotaxis, (2) Trans-endothelial and intranodal movement on the reticular network, (3) Active regulation of cellular transcription and translation in the lymph node (including leukocyte associated cellular regulatory networks) and (4) Chemokine receptors regulating the movement of cells out of the lymph node. This work provides a first transcriptome analysis of bovine lymph node responses in tick-infested cattle. Findings show a dynamic immune response to tick infestation for the Bonsmara cattle breed, and that suppression of the maturation of the cattle hosts' immunity is especially evident during the larval feeding stages.

A genetic and immunological comparison of tick-resistance in beef cattle following artificial infestation with Rhipicephalus ticks

Host resistance to ticks can be explored as a possible approach of combating tick infestations to complement the existing unsustainable tick control methods. Thirty-six beef cattle animals were used, consisting of Angus, Brahman and Nguni breeds, with each breed contributing 12 animals. Half of the animals per breed were artificially challenged with Rhipicephalus microplus and the other half with R. decoloratus unfed larvae per animal. Skin biopsies and blood samples were collected pre-infestation and 12 h post-infestation from the feeding sites of visibly engorging ticks. The success rate of the ticks was high and had an influence even at the early time point. Increased lymphocytes and blood urea nitrogen levels as well as decreased levels of segmented neutrophils were observed in the Angus, which were the opposite of those in the Brahman and Nguni. The increase in cholesterol, which was highest in the Angus and lowest in the Nguni, may be due to altered protein metabolism. The expression profiles of genes TRAF6, TBP, LUM and B2M were significantly different among breeds. Five genes (CCR1, TLR5, TRAF6, TBP, BDA20) had increased or constant expression post-infestation, whereas the expression of CXCL8, IL-10 and TNF-α decreased or remained the same after tick challenge. Genes that showed variation are involved in discouraging long-term supply of blood meal to the tick and those associated with immune responses. The gene LUM is a potential biomarker for tick resistance in cattle. The response to infestation by the breeds was consistent across the tick species.

[Immunomodulatory effect of tick saliva in pathogen transmission]

Ticks are the most important vectors of pathogens in human and veterinary medicine. These strictly haematophagous acarines produce a saliva containing a variety of bioactive molecules affecting host pharmacology and immunity. This process is vital for hard ticks to prevent rejection by the host during the blood meal that lasts several days. All actors involved in the immunity interplay are impacted by this saliva, the innate immunity being represented by resident and migrating immune cells, as well as the T and B lymphocytes of the adaptive immune system. The skin plays a key role in vector-borne diseases. During the long co-evolution with the tick, the infectious agents benefit from this favorable environment to be transmitted efficiently into the skin and to multiply in the vertebrate host. Therefore, the saliva is an important virulence booster, which enhances substantially their pathogenicity.

Immunomodulatory and morphophysiological effects of Rhipicephalus sanguineus s. l. (Acari: Ixodidae) salivary gland extracts

Rhipicephalus sanguineus s. l. is popularly known as the "brown dog tick" since dogs are its preferential hosts, but the species has been reported to parasitize other mammals, including humans, with significant medical-veterinary importance since it transmits several important pathogenic agents during the feeding period. The tick saliva is a complex mixture that has several functions, including the capability to modulate the hemostatic, inflammatory and immunologic systems of the host, allowing pathogens to settle. Despite knowledge about the immunosuppressive action of tick saliva, little is known about the mechanisms involved in this process and the morphophysiological effects caused by exposure to the salivary gland extract, taking into consideration the different periods of the glandular cycle. Thus, the objective of this study was to analyze the in vitro effects of salivary gland extracts obtained from R. sanguineus s. l. females fed on host rabbits for two (SGE2 - Salivary Gland Extracts of 2 days) and four days (SGE4 - Salivary Gland Extracts of 4 days) on J774 cells (monocyte macrophage cell line) and verify the occurrence of morphological and immunomodulatory alterations in these cells when exposed to different concentrations of these extracts. The results showed that: (i) SGE2 and SGE4 at the concentration of 4 μg/mL presented cytotoxicity to the J774 cells exposed for 24 and 48 hours; (ii) SGE2 at the concentrations of 2 μg/mL(48-hour exposure) and 1 μg/mL (24-hour exposure) and SGE4 at the concentrations of 2 and 1 μg/mL (48-hour exposure) showed proinflammatory activity, confirmed by the increased secretion of NO and proinflammatory cytokine (IL-2), and the presence of morphological characteristics detected by microscopy; and (iii) SGE2 and SGE4 at the concentrations of 0.5 and 0.1 μg/mL had immunomodulatory activity, demonstrated by decreases in the secretion of NO and proinflammatory cytokines (IL2, IL-6 and TNF-α) and increase in the synthesis of IL-10, confirmed by the morphophysiological analysis. These unprecedented data are extremely relevant for future research to identify the processes involved in the ectoparasite-host relationship, as well to develop more efficient tick control strategies.

Morphological evaluation of the liver in Wistar rats inoculated with Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) salivary gland extracts

The Rhipicephalus sanguineus is considered a species of medical and veterinary importance. The feeding process of these animals occurs due to the combined action of their mouthparts and the saliva produced by the salivary glands, vital organs for the biological success of the ticks. In addition, these glands act as storage sites for the pathogens transmitted to the host through the inoculation of the saliva. In this sense, the present study had the objective to analyze the behavior of male Wistar rat hepatic cells submitted to in vivo application of the salivary gland extract (SGE) obtained from R. sanguineus female ticks. The study involved five groups (four male adults each): CG (non-inoculated individuals); PBS1 (one phosphate buffer saline injection); PBS2 (two PBS injections); SGE1 (one injection of SGE at 0.04 μg/μL) and SGE2 (two injections of SGE at 0.04 μg/μL). After the exposures, the livers were removed and submitted to the following histological and histochemical stains: HE, toluidine blue, Xylidine Ponceau, alcian blue/PAS, and osmium-imidazole. The results showed that both the PBS and the SGE caused hepatic moderate alterations, such as: (a) emergence of lipid plaques among the hepatic cords; (b) cytoplasmic vacuolation of the hepatic cells; (c) hepatocytes showing pyknotic nuclei; (d) presence of homogeneous or granular secretion in the cytoplasm of the hepatocytes. Despite the slight morphological alterations observed in the hepatic cells and tissue, the latter did not show signs of disorganization after the exposure to the extracts.

Ticks and Tick-Borne Infections: Complex Ecology, Agents, and Host Interactions

Ticks transmit the most diverse array of infectious agents of any arthropod vector. Both ticks and the microbes they transmit are recognized as significant threats to human and veterinary public health. This article examines the potential impacts of climate change on the distribution of ticks and the infections they transmit; the emergence of novel tick-borne pathogens, increasing geographic range and incidence of tick-borne infections; and advances in the characterization of tick saliva mediated modulation of host defenses and the implications of those interactions for transmission, establishment, and control of tick infestation and tick-borne infectious agents.

Expression Patterns of Host Inflammatory Cytokine Genes during Infestation with Haemaphysalis longicornis, a Zoonotic Vector, in Blood Sucking Periods

Tick saliva is critically important for continuous attachment to the host, blood feeding for days, and transmission of tick-borne pathogens. To characterize the patterns of inflammatory cytokine gene expression during its attachment and blood sucking time, peripheral blood samples of rabbits infested with Haemaphysalis longicornis ticks were collected at different intervals. Blood histamine concentration was evaluated as well as gene encoding IFN-γ, TNF-α, IL-2, IL-6, IL-4, and IL-10 were compared with non-infested rabbits. Blood histamine concentration of tick-infested rabbits during fast feeding time was significantly higher than that of non-infested rabbits. In both nymph and adult tick infested rabbits, expression of TNF-α and IFN-γ genes were decreased significantly (P<0.05), while expression of IL-4, IL-6, and IL-10 were increased 1.3 to 7 folds in adult infested rabbits with the exception of IL-6 that was significantly (P<0.05) decreased in nymph infested rabbits. IL-2 was not expressed in either nymph or adult infestation. H. longicornis saliva is capable of modulate host responses through a complex correlation with histamine and Th1, Th2 mediated cytokines that suppress the inflammatory responses directed toward inflammatory mediators introduced into the host during tick feeding.

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.

Tick-Borne Viruses and Biological Processes at the Tick-Host-Virus Interface

Ticks are efficient vectors of arboviruses, although less than 10% of tick species are known to be virus vectors. Most tick-borne viruses (TBV) are RNA viruses some of which cause serious diseases in humans and animals world-wide. Several TBV impacting human or domesticated animal health have been found to emerge or re-emerge recently. In order to survive in nature, TBV must infect and replicate in both vertebrate and tick cells, representing very different physiological environments. Information on molecular mechanisms that allow TBV to switch between infecting and replicating in tick and vertebrate cells is scarce. In general, ticks succeed in completing their blood meal thanks to a plethora of biologically active molecules in their saliva that counteract and modulate different arms of the host defense responses (haemostasis, inflammation, innate and acquired immunity, and wound healing). The transmission of TBV occurs primarily during tick feeding and is a complex process, known to be promoted by tick saliva constituents. However, the underlying molecular mechanisms of TBV transmission are poorly understood. Immunomodulatory properties of tick saliva helping overcome the first line of defense to injury and early interactions at the tick-host skin interface appear to be essential in successful TBV transmission and infection of susceptible vertebrate hosts. The local host skin site of tick attachment, modulated by tick saliva, is an important focus of virus replication. Immunomodulation of the tick attachment site also promotes co-feeding transmission of viruses from infected to non-infected ticks in the absence of host viraemia (non-viraemic transmission). Future research should be aimed at identification of the key tick salivary molecules promoting virus transmission, and a molecular description of tick-host-virus interactions and of tick-mediated skin immunomodulation. Such insights will enable the rationale design of anti-tick vaccines that protect against disease caused by tick-borne viruses.

Interaction between saliva's adenosine and tick parasitism: effects on feeding and reproduction

Background

It has recently been demonstrated that saliva from Rhipicephalus sanguineus ticks contains adenosine (ADO) and prostaglandin E2 (PGE2), two non-protein molecules that have significant immunomodulatory properties. These molecules can inhibit cytokine production by dendritic cells (DCs), while also reducing the expression of CD40 in these cells. However, more studies are needed for a better understanding of their participation in the feeding of ticks in vivo. This work, therefore, evaluated the importance of ADO during tick infestations. Mice were infested with adult ticks (3 couples/mouse), and their skin was collected at the tick-infested site (3rd and 7th day), and mRNA for receptors of ADO was quantified by real-time PCR.

Results

Tick infestation increased by four and two times the expression of the A2b and A3v1 receptors on day 3, respectively, while expression of other ADO receptors was unaltered. In addition, we treated mice (n = 10/group) daily with 8-(p-Sulfophenyl)theophylline, 8-pSPT, 20 mg/kg, i.p.), a non-selective antagonist of ADO receptors, and evaluated the performance of ticks during infestations. Female ticks fed on 8-pSPT-treated mice presented a reduction in their engorgement, weight and hatching rates of egg masses, and survival times of larvae compared to the same parameters presented by ticks in the control group. To investigate if these 8-pSPT-treated mice presented altered immune responses, we performed three tick infestations and collected their lymph node cells to determine the percentages and activation state of DCs and cytokine production by lymphocytes by flow cytometry (Cytometric Bead Array technique, CBA). Our data showed that 8-pSPT-treated mice presented an increase in the percentage of DCs as well as of their stimulatory and co-stimulatory molecules (CD40, CD80 and MHCII). Regarding production of T cell cytokines, we observed a significant increase in the levels of IL-2 and a significant decrease in IL-10, IL-17, TNF-α and IFN-γ cytokines.

Conclusions

These results suggest that ADO produced by ticks helps them feed and reproduce and that this effect may be due to modulation of host DCs and T cells.

Potential pharmacological use of salivary compounds from hematophagous organisms

Introducción. La saliva de los artrópodos hematófagos contiene un arsenal de compuestos que les permite acceder a la sangre de sus hospederos vertebrados sin ser detectados.Objetivo. Explorar los compuestos salivares de insectos hematófagos que tienen propiedades vasodilatadoras, anticoagulantes, antiinflamatorias, inmunomoduladoras y anestésicas, las cuales se pueden aprovechar por su alto potencial farmacológico.Materiales y métodos. Se realizó una revisión no sistemática de la literatura mediante búsqueda electrónica en las bases de datos PubMed, EMBASE, OvidSP y ScienceDirect; la búsqueda no se limitó por fecha, idioma ni tipo de artículo. Se buscaron artículos sobre los compuestos salivares de los insectos hematófagos, cuyo tema central fuese los efectos en la hemostasia, inmunomodulación y uso farmacológico. Se encontraron 59 artículos que cumplían con los criterios para ser incluidos en la revisión.Conclusión. La saliva de los insectos hematófagos posee gran variedad de moléculas, lo que ofrece una fuente de investigación y un potencial incalculable para el descubrimiento de compuestos que podrían llegar a tener utilidad farmacológica.

Cellular response in the tick feeding site in crossbred cattle artificially infested by Rhipicephalus microplus

Ticks and tick-borne diseases are of global importance and can cause serious economic losses to cattle-raising businesses. However, only few attempts have been made to describe the relationships between various cellular immune components and tick counts of, and therefore resistance to, Rhipicephalus microplus. The present study evaluated the late inflammatory cellular response and dermal dendritic cells at the attachment site in naturally presensitized bovines, artificially infested by R. microplus ticks. Twenty-two crossbred (Holstein × Gir) male experimental cattle were artificially infested with approximately 10,000 larvae of R. microplus. Parasitic infestation was determined by counting the engorged female ticks (4.5-8.0 mm in diameter) at the 21st day after artificial infestation. Biopsies (6 mm) were taken prior to the infestation and along with the tick count from the right pinna of each animal, and examined with histological techniques and immunohistochemistry using S100 protein. Inflammatory cell counts were conducted in the sections stained with the May-Grünwald Giemsa technique, and immunostained dermal dendritic cells were evaluated and classified in scores ranging from 0 to 4. An average of 39.2 ticks per animal was found. Eosinophils (47.8%) constituted the major portion of the cellular infiltrate, followed by mononuclear cells (28.3%), neutrophils (14.4%), and basophils (0% to approximately 2%). The dendritic cell count shows a considerable population in the dermis, with pre- and post-infestation mean scores of 1.54 and 1.89, respectively; these scores were not significantly different. Our results pointed out the importance of the cellular response in the cattle resistance to ticks.

Effect of the saliva from different triatomine species on the biology and immunity of TLR-4 ligand and Trypanosoma cruzi-stimulated dendritic cells

Background

Triatomines are blood-sucking vectors of Trypanosoma cruzi, the causative agent of Chagas disease. During feeding, triatomines surpass the skin host response through biomolecules present in their saliva. Dendritic cells (DCs) play a crucial role in the induction of the protection to aggressive agents, including blood-sucking arthropods. Here, we evaluated if salivary components of triatomines from different genera evade the host immunity by modulating the biology and the function of LPS- or T. cruzi-stimulated DCs.

Methods

Saliva of Panstrongylus lignarius, Meccus pallidipennis, Triatoma lecticularia and Rhodnius prolixus were obtained by dissection of salivary glands and the DCs were obtained from the differentiation of mouse bone marrow precursors.

Results

The differentiation of DCs was inhibited by saliva of all species tested. Saliva differentially inhibited the expression of MHC-II, CD40, CD80 and CD86 in LPS-matured DCs. Except for the saliva of R. prolixus, which induced IL-6 cytokine production, TNF-α, IL-12 and IL-6 were inhibited by the saliva of the other three tested species and IL-10 was increased in all of them. Saliva per se, also induced the production of IL-12, IL-6 and IL-10. Only the saliva of R. prolixus induced DCs apoptosis. The presence of PGE₂ was not detected in the saliva of the four triatomines studied. Finally, T. cruzi invasion on DCs is enhanced by the presence of the triatomine saliva.

Conclusions

These results demonstrate that saliva from different triatomine species exhibit immunomodulatory effects on LPS and T. cruzi-stimulated DCs. These effects could be related to hematophagy and transmission of T. cruzi during feeding.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1890-x) contains supplementary material, which is available to authorized users.

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.

Immunosuppressive effects of Amblyomma cajennense tick saliva on murine bone marrow-derived dendritic cells

Background

Dendritic cells (DCs) are professional antigen-presenting cells with vital roles in the activation of host immunity. Ticks are bloodsucking arthropods that secrete bioactive compounds with immunomodulatory properties via their saliva. It is known that some tick species modulate the biology of DCs with different intensities; however, studies on Amblyomma cajennense, the Cayenne tick, have not yet been performed, although this species is considered one of the most capable of modulating immune responses of different hosts.

Methods

Engorged female ticks were stimulated with dopamine to induce salivation, and saliva was pooled. The effects of tick saliva on the biology of dendritic cells were assessed by examining DC differentiation, maturation, migration, cellular viability, cytokine production and expression of surface markers by flow cytometry and ELISA. Competitive enzyme immunoassays (EIA) were used to measure saliva prostaglandin-E₂ (PGE₂). Statistical significance was determined by ANOVA followed by Tukey’s post-test or by the Kruskal-Wallis test with the Dunns post-test.

Results

In this work, we demonstrated that the presence of A. cajennense saliva to bone marrow cultures inhibit DC differentiation. This inhibition was not accompanied by inhibition or induction of stimulatory and co-stimulatory molecules such as MHC-II, CD40, CD80 or CD86. Immature and mature DCs that were pre-exposed to saliva showed reduced migration toward the chemokines RANTES and MIP-3β. This inhibition was associated to a reduced expression of CCR5 (the receptor for RANTES) or CCR7 (the receptor for MIP-3β) induced by the presence of saliva in the cultures. Tick saliva also inhibited IL-12p40, IL-6 and TNF-α in a concentration-dependent manner while potentiating IL-10 cytokine production by DCs stimulated with Toll-like receptor-4 ligand. Additionally, A. cajennense tick saliva inhibited the expression of CD40 and CD86 in mature DCs while potentiating the expression of PD-L1. PGE₂ was detected as one of the constituents of saliva at a concentration of ~ 80 ng/ml, and we believe that most of the results reported herein are due to the presence of PGE₂.

Conclusions

These results help to understand the tick-host interaction and demonstrate that A. cajennense ticks appear to have mechanisms for modulating host immune cells, including DCs.

Monitoring human tick-borne disease risk and tick bite exposure in Europe: available tools and promising future methods

Ticks are the main vector for infectious disease pathogens in both humans and animals, and tick-borne diseases are currently spreading throughout Europe. Various surveillance methods have been developed to estimate the burden and risk of tick-borne diseases and host exposure to tick bites. The ultimate aims of these approaches are to determine the risk level of a tick-borne disease in a given area, determine its health priority, identify the at-risk population and propose specific countermeasures or complementary studies as needed. The purpose of this review is to present the current methods for monitoring the circulation of tick-borne diseases and to highlight the use of salivary antigens as original and recently developed serological tools that could be useful for tick bite risk assessment and could improve the current surveillance methods.

Murine cutaneous responses to the rocky mountain spotted fever vector, Dermacentor andersoni, feeding

Tick salivary glands produce complex cocktails of bioactive molecules that facilitate blood feeding and pathogen transmission by modulating host hemostasis, pain/itch responses, wound healing, and both innate and adaptive immunity. In this study, cutaneous responses at Dermacentor andersoni bite-sites were analyzed using Affymetrix mouse genome arrays and histopathology at 12, 48, 96 and 120 h post- infestation (hpi) during primary infestations and 120 hpi during secondary infestations. The microarray data suggests: (1) chemotaxis of neutrophils, monocytes, and other cell types; (2) production and scavenging of reactive oxygen species; and, (3) keratin- based wound healing responses. Histological analysis supported the microarray findings. At 12 hpi, a mild inflammatory infiltrate was present in the dermis, especially concentrated at the junction between dermal connective tissue and underlying adipose tissue. A small lesion was located immediately under the hypostome and likely represents the feeding “pool.” Surprisingly, at 48 hpi, the number of inflammatory cells had not increased from 12 hpi, perhaps mirroring the reduction in gene expression seen at this time point. The feeding lesion is very well defined, and extravasated erythrocytes are readily evident around the hypostome. By 96 hpi, the inflammatory infiltrate has increased dramatically and the feeding lesion appears to have moved deeper into the dermis. At 120 hpi, most of the changes at 96 hpi are intensified. The infiltrate is very dense, the epidermis is markedly thickened, the feeding lesion is poorly defined and the dermal tissue near the hypostome appears to be loosing its normal architecture. In conclusion, during D. andersoni feeding infiltration of inflammatory cells increases across time concurrent with significant changes in the epidermal and dermal compartments near the feeding tick. The importance of changes in the epidermal layer in the host response to ticks is not known, however, it is possible the host attempts to “slough off” the tick by greatly increasing epithelial cell replication.

Ménage à trois: Borrelia, dendritic cells, and tick saliva interactions

Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, is inoculated into the skin during an Ixodes tick bite where it is recognised and captured by dendritic cells (DCs). However, considering the propensity of Borrelia to disseminate, it would appear that DCs fall short in mounting a robust immune response against it. Many aspects of the DC-driven immune response to Borrelia have been examined. Recently, components of tick saliva have been identified that sabotage DC responses and aid Borrelia infection. In this review, we summarise what is currently known about the immune response of DCs to Borrelia and explore the mechanisms by which Borrelia manages to circumvent this immune response, with or without the help of tick salivary proteins.

Dendritic Cell Plasticity in Tumor-Conditioned Skin: CD14(+) Cells at the Cross-Roads of Immune Activation and Suppression

Tumors abuse myeloid plasticity to re-direct dendritic cell (DC) differentiation from T cell stimulatory subsets to immune-suppressive subsets that can interfere with anti-tumor immunity. Lined by a dense network of easily accessible DC the skin is a preferred site for the delivery of DC-targeted vaccines. Various groups have recently been focusing on functional aspects of DC subsets in the skin and how these may be affected by tumor-derived suppressive factors. IL-6, Prostaglandin-E2, and IL-10 were identified as factors in cultures of primary human tumors responsible for the inhibited development and activation of skin DC as well as monocyte-derived DC. IL-10 was found to be uniquely able to convert fully developed DC to immature macrophage-like cells with functional M2 characteristics in a physiologically highly relevant skin explant model in which the phenotypic and functional traits of “crawl-out” DC were studied. Mostly from mouse studies, the JAK2/STAT3 signaling pathway has emerged as a “master switch” of tumor-induced immune suppression. Our lab has additionally identified p38-MAPK as an important signaling element in human DC suppression, and recently validated it as such in ex vivo cultures of single-cell suspensions from melanoma metastases. Through the identification of molecular mechanisms and signaling events that drive myeloid immune suppression in human tumors, more effective DC-targeted cancer vaccines may be designed.

Ticks and tick-borne pathogens at the cutaneous interface: host defenses, tick countermeasures, and a suitable environment for pathogen establishment

Ticks are unique among hematophagous arthropods by continuous attachment to host skin and blood feeding for days; complexity and diversity of biologically active molecules differentially expressed in saliva of tick species; their ability to modulate the host defenses of pain and itch, hemostasis, inflammation, innate and adaptive immunity, and wound healing; and, the diverse array of infectious agents they transmit. All of these interactions occur at the cutaneous interface in a complex sequence of carefully choreographed host defense responses and tick countermeasures resulting in an environment that facilitates successful blood feeding and establishment of tick-borne infectious agents within the host. Here, we examine diverse patterns of tick attachment to host skin, blood feeding mechanisms, salivary gland transcriptomes, bioactive molecules in tick saliva, timing of pathogen transmission, and host responses to tick bite. Ticks engage and modulate cutaneous and systemic immune defenses involving keratinocytes, natural killer cells, dendritic cells, T cell subpopulations (Th1, Th2, Th17, Treg), B cells, neutrophils, mast cells, basophils, endothelial cells, cytokines, chemokines, complement, and extracellular matrix. A framework is proposed that integrates tick induced changes of skin immune effectors with their ability to respond to tick-borne pathogens. Implications of these changes are addressed. What are the consequences of tick modulation of host cutaneous defenses? Does diversity of salivary gland transcriptomes determine differential modulation of host inflammation and immune defenses and therefore, in part, the clades of pathogens effectively transmitted by different tick species? Do ticks create an immunologically modified cutaneous environment that enhances specific pathogen establishment? Can tick saliva molecules be used to develop vaccines that block pathogen transmission?

Ixodes scapularis saliva mitigates inflammatory cytokine secretion during Anaplasma phagocytophilum stimulation of immune cells

Background

Ixodes scapularis saliva enables the transmission of infectious agents to the mammalian host due to its immunomodulatory, anesthetic and anti-coagulant properties. However, how I. scapularis saliva influences host cytokine secretion in the presence of the obligate intracellular rickettsial pathogen Anaplasma phagocytophilum remains elusive.

Methods

Bone marrow derived macrophages (BMDMs) were stimulated with pathogen associated molecular patterns (PAMPs) and A. phagocytophilum. Cytokine secretion was measured in the presence and absence of I. scapularis saliva. Human peripheral blood mononuclear cells (PBMCs) were also stimulated with Tumor Necrosis Factor (TNF)-α in the presence and absence of I. scapularis saliva and interleukin (IL)-8 was measured.

Results

I. scapularis saliva inhibits inflammatory cytokine secretion by macrophages during stimulation of Toll-like (TLR) and Nod-like receptor (NLR) signaling pathways. The effect of I. scapularis saliva on immune cells is not restricted to murine macrophages because decreasing levels of interleukin (IL)-8 were observed after TNF-α stimulation of human peripheral blood mononuclear cells. I. scapularis saliva also mitigates pro-inflammatory cytokine response by murine macrophages during challenge with A. phagocytophilum.

Conclusions

These findings suggest that I. scapularis may inhibit inflammatory cytokine secretion during rickettsial transmission at the vector-host interface.

Effect of tick saliva on immune interactions between Borrelia afzelii and murine dendritic cells

Interaction between mouse dendritic cells (DCs) and Borrelia afzelii spirochetes was monitored on three different levels: phagocytosis of spirochetes by DCs, production of cytokines by Borrelia-stimulated DCs and the ability of Borrelia-exposed DCs to activate specific CD4+ T lymphocytes. The effect of Ixodes ricinus tick saliva on each of these interactions was examined. Tick saliva was shown to decrease the number of phagocytosing DCs. The ability of Borrelia-exposed DCs to induce both proliferation and IL-2 production by specific CD4+ T cells was significantly reduced by tick saliva. And surprisingly, we have shown an inhibitory effect of tick saliva on the production of both Th1 (TNF-α and IL-6) and Th2 (IL-10) cytokines by DCs. Our data reveal a complex inhibitory effect of tick saliva on Borrelia-DCs interaction.

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.

Deconstructing tick saliva: non-protein molecules with potent immunomodulatory properties

Dendritic cells (DCs) are powerful initiators of innate and adaptive immune responses. Ticks are blood-sucking ectoparasite arthropods that suppress host immunity by secreting immunomodulatory molecules in their saliva. Here, compounds present in Rhipicephalus sanguineus tick saliva with immunomodulatory effects on DC differentiation, cytokine production, and costimulatory molecule expression were identified. R. sanguineus tick saliva inhibited IL-12p40 and TNF-α while potentiating IL-10 cytokine production by bone marrow-derived DCs stimulated by Toll-like receptor-2, -4, and -9 agonists. To identify the molecules responsible for these effects, we fractionated the saliva through microcon filtration and reversed-phase HPLC and tested each fraction for DC maturation. Fractions with proven effects were analyzed by micro-HPLC tandem mass spectrometry or competition ELISA. Thus, we identified for the first time in tick saliva the purine nucleoside adenosine (concentration of ∼110 pmol/μl) as a potent anti-inflammatory salivary inhibitor of DC cytokine production. We also found prostaglandin E(2) (PGE(2) ∼100 nM) with comparable effects in modulating cytokine production by DCs. Both Ado and PGE(2) inhibited cytokine production by inducing cAMP-PKA signaling in DCs. Additionally, both Ado and PGE(2) were able to inhibit expression of CD40 in mature DCs. Finally, flow cytometry analysis revealed that PGE(2), but not Ado, is the differentiation inhibitor of bone marrow-derived DCs. The presence of non-protein molecules adenosine and PGE(2) in tick saliva indicates an important evolutionary mechanism used by ticks to subvert host immune cells and allow them to successfully complete their blood meal and life cycle.

Rhipicephalus microplus salivary gland molecules induce differential CD86 expression in murine macrophages

Background

Tick parasitism is a major impediment for cattle production in many parts of the world. The southern cattle tick, Rhipicephalus (Boophilus) microplus, is an obligate hematophagous parasite of domestic and wild animals that serves as vector of infectious agents lethal to cattle. Tick saliva contains molecules evolved to modulate host innate and adaptive immune responses which facilitates blood feeding and pathogen transmission. Tick feeding promotes CD4 T cell polarization to a Th2 profile usually accompanied by down-regulation of Th1 cytokines through as yet undefined mechanisms. Co-stimulatory molecules on antigen presenting cells are central to development of T cell responses including Th1 and Th2 responses. Tick induced changes to antigen presenting cell signal transduction pathways are largely unknown. Here we document the ability of R. microplus salivary gland extracts (SGE) to effect differential CD86 expression.

Results

We examined changes in co-stimulatory molecule expression in murine RAW 264.7 cells in response to R. microplus SGE exposure in the presence of the toll-like receptor 4 (TLR4) ligand, LPS. After 24 hrs, CD86, but not CD80, was preferentially up-regulated on mouse macrophage RAW 264.7 cells when treated with SGE and then LPS, but not SGE alone. CD80 and CD40 expression was increased with LPS, but the addition of SGE did not alter expression. Higher concentrations of SGE were less effective at increasing CD86 RNA expression. The addition of mitogen or extracellular kinase (MEK) inhibitor, PD98059, significantly reduced the ability for SGE to induce CD86 expression, indicating activation of MEK is necessary for SGE induced up-regulation.

Conclusions

Molecules in SGE of R. microplus have a concentration-dependent effect on differential up-regulation of CD86 in a macrophage cell line activated by the TLR4 ligand, LPS. This CD86 up-regulation is at least partially dependent on the ERK1/2 pathway and may serve to promote Th2 polarization of the immune response.

Targeting Toll-like receptor 7/8 enhances uptake of apoptotic leukemic cells by monocyte-derived dendritic cells but interferes with subsequent cytokine-induced maturation

Therapeutic vaccination with dendritic cells (DC) is an emerging investigational therapy for eradication of minimal residual disease in acute myeloid leukemia. Various strategies are being explored in manufacturing DC vaccines ex vivo, e.g., monocyte-derived DC (MoDC) loaded with leukemia-associated antigens (LAA). However, the optimal source of LAA and the choice of DC-activating stimuli are still not well defined. Here, loading with leukemic cell preparations (harboring both unknown and known LAA) was explored in combination with a DC maturation-inducing cytokine cocktail (CC; IL-1β, IL-6, TNF-α, and PGE₂) and Toll-like receptor ligands (TLR-L) to optimize uptake. Since heat shock induced apoptotic blasts were more efficiently taken up than lysates, we focused on uptake of apoptotic leukemic cells. Uptake of apoptotic blast was further enhanced by the TLR7/8-L R848 (20–30%); in contrast, CC-induced maturation inhibited uptake. CC, and to a lesser extent R848, enhanced the ability of MoDC to migrate and stimulate T cells. Furthermore, class II-associated invariant chain peptide expression was down-modulated after R848- or CC-induced maturation, indicating enhanced processing and presentation of antigenic peptides. To improve both uptake and maturation, leukemic cells and MoDC were co-incubated with R848 for 24 h followed by addition of CC. However, this approach interfered with CC-mediated MoDC maturation as indicated by diminished migratory and T cell stimulatory capacity, and the absence of IL-12 production. Taken together, our data demonstrate that even though R848 improved uptake of apoptotic leukemic cells, the sequential use of R848 and CC is counter-indicated due to its adverse effects on MoDC maturation.