Reciprocal regulation of NF-kB (Relish) and Subolesin in the tick vector, Ixodes scapularis

Validation of heat-inducible Ixodes scapularis HSP70 and tick-specific 3xP3 promoters in ISE6 cells

Ixodes scapularis is an important vector of many pathogens, including the causative agent of Lyme disease. The gene function studies in I. scapularis and other ticks are hampered by the lack of genetic tools, including an inducible promoter for temporal control over transgene-encoding protein or double-stranded RNA. We characterized an intergenic sequence upstream of a heat shock protein 70 (HSP70) gene that can drive Renilla luciferase and mCherry expression in the I. scapularis cell line ISE6 (IsHSP70). In another construct, we replaced the Drosophila melanogaster minimal HSP70 promoter of the 3xP3 promoter with a minimal portion of IsHSP70 promoter and generated an I. scapularis-specific 3xP3 (Is3xP3) promoter. Both IsHSP70 and Is3xP3 have a heat-inducible expression of mCherry fluorescence in ISE6 cells with an approximately 10-fold increase in the percentage of fluorescent cells upon 2 h heat shock. These promoters described will be valuable tools for gene function studies.

Arthropod promoters for genetic control of disease vectors

Vector-borne diseases (VBDs) impose devastating effects on human health and a heavy financial burden. Malaria, Lyme disease, and dengue fever are just a few examples of VBDs that cause severe illnesses. The current strategies to control VBDs consist mainly of environmental modification and chemical use, and to a small extent, genetic approaches. The genetic approaches, including transgenesis/genome modification and gene-drive technologies, provide the basis for developing new tools for VBD prevention by suppressing vector populations or reducing their capacity to transmit pathogens. The regulatory elements such as promoters are required for a robust sex-, tissue-, and stage-specific transgene expression. As discussed in this review, information on the regulatory elements is available for mosquito vectors but is scant for other vectors.

Subolesin knockdown in tick cells provides insights into vaccine protective mechanisms

Ticks as obligate blood-feeding arthropod vectors of pathogenic viruses, bacteria, protozoa and helminths associated with prevalent tick-borne diseases (TBDs) worldwide. These arthropods constitute the second vector after mosquitoes that transmit pathogens to humans and the first vector in domestic animals. Vaccines constitute the safest and more effective approach to control tick infestations and TBDs, but research is needed to identify new antigens and improve vaccine formulations. The tick protein Subolesin (Sub) is a well-known vaccine protective antigen with a highly conserved sequence at both gene and protein levels in the Ixodidae and among arthropods and vertebrates. In this study, transcriptomics and proteomics analyses were conducted together with graph theory data analysis in wild type and Sub knockdown (KD) tick ISE6 cells in order to identify and characterize the functional implications of Sub in tick cells. The results support a key role for Sub in the regulation of gene expression in ticks and the relevance of this antigen in vaccine development against ticks and TBDs. Proteins with differential representation in response to Sub KD provide insights into vaccine protective mechanisms and candidate tick protective antigens.

Towards modelling tick-virus interactions using the weakly pathogenic Sindbis virus: Evidence that ticks are competent vectors

Most tick-borne viruses (TBVs) are highly pathogenic and require high biosecurity, which severely limits their study. We found that Sindbis virus (SINV), predominantly transmitted by mosquitoes, can replicate in ticks and be subsequently transmitted, with the potential to serve as a model for studying tick-virus interactions. We found that both larval and nymphal stages of Rhipicephalus haemaphysaloides can be infected with SINV-wild-type (WT) when feeding on infected mice. SINV replicated in two species of ticks (R. haemaphysaloides and Hyalomma asiaticum) after infecting them by microinjection. Injection of ticks with SINV expressing enhanced Green Fluorescent Protein (eGFP) revealed that SINV-eGFP specifically aggregated in the tick midguts for replication. During blood-feeding, SINV-eGFP migrated from the midguts to the salivary glands and was transmitted to a new host. SINV infection caused changes in expression levels of tick genes related to immune responses, substance transport and metabolism, cell growth and death. SINV mainly induced autophagy during the early stage of infection; with increasing time of infection, the level of autophagy decreased, while the level of apoptosis increased. During the early stages of infection, the transcript levels of immune-related genes were significantly upregulated, and then decreased. In addition, SINV induced changes in the transcription levels of some functional genes that play important roles in the interactions between ticks and tick-borne pathogens. These results confirm that the SINV-based transmission model between ticks, viruses, and mammals can be widely used to unravel the interactions between ticks and viruses.

Validation of a heat-inducible Ixodes scapularis HSP70 promoter and developing a tick-specific 3xP3 promoter sequence in ISE6 cells

Ixodes scapularis is an important vector of many pathogens, including the causative agent of Lyme disease, tick-borne encephalitis, and anaplasmosis. The study of gene function in I. scapularis and other ticks has been hampered by the lack of genetic tools, such as an inducible promoter to permit temporal control over transgenes encoding protein or double-stranded RNA expression. Studies of vector-pathogen relationships would also benefit from the capability to activate anti-pathogen genes at different times during pathogen infection and dissemination. We have characterized an intergenic sequence upstream of the heat shock protein 70 (HSP70) gene that can drive Renilla luciferase expression and mCherry fluorescence in the I. scapularis cell line ISE6. In another construct, we replaced the Drosophila melanogaster minimal HSP70 promoter in the synthetic 3xP3 promoter with a minimal portion of the I. scapularis HSP70 promoter and generated an I. scapularis specific 3xP3 (Is3xP3) promoter. Both promoter constructs, IsHSP70 and Is3xP3, allow for heat-inducible expression of mCherry fluorescence in ISE6 cells with an approximately 10-fold increase in the percentage of fluorescent positive cells upon exposure to a 2 h heat shock. These promoters described here will be valuable tools for gene function studies and temporal control of gene expression, including anti-pathogen genes.

Tick extracellular vesicles in host skin immunity and pathogen transmission

Ticks can transmit a variety of human pathogens, including intracellular and extracellular bacteria, viruses, and protozoan parasites. Historically, their saliva has been of immense interest due to its anticoagulant, anti-inflammatory, and anesthetic properties. Only recently, it was discovered that tick saliva contains extracellular vesicles (EVs). Briefly, it has been observed that proteins associated with EVs are important for multiple tick-borne intracellular microbial lifestyles. The impact of tick EVs on viral and intracellular bacterial pathogen transmission from the tick to the mammalian host has been shown experimentally. Additionally, tick EVs interact with the mammalian skin immune system at the bite site. The interplay between tick EVs, the transmission of pathogens, and the host skin immune system affords opportunities for future research.

Dynamic Regulation of NF-κB Response in Innate Immunity: The Case of the IMD Pathway in Drosophila

Metazoans have developed strategies to protect themselves from pathogenic attack. These preserved mechanisms constitute the immune system, composed of innate and adaptive responses. Among the two kinds, the innate immune system involves the activation of a fast response. NF-κB signaling pathways are activated during infections and lead to the expression of timely-controlled immune response genes. However, activation of NF-κB pathways can be deleterious when uncontrolled. Their regulation is necessary to prevent the development of inflammatory diseases or cancers. The similarity of the NF-κB pathways mediating immune mechanisms in insects and mammals makes Drosophila melanogaster a suitable model for studying the innate immune response and learning general mechanisms that are also relevant for humans. In this review, we summarize what is known about the dynamic regulation of the central NF-κB-pathways and go into detail on the molecular level of the IMD pathway. We report on the role of the nuclear protein Akirin in the regulation of the NF-κB Relish immune response. The use of the Drosophila model allows the understanding of the fine-tuned regulation of this central NF-κB pathway.

Tick Importin-α Is Implicated in the Interactome and Regulome of the Cofactor Subolesin

Ticks and tick-borne diseases (TBDs) represent a burden for human and animal health worldwide. Currently, vaccines constitute the safest and most effective approach to control ticks and TBDs. Subolesin (SUB) has been identified as a vaccine antigen for the control of tick infestations and pathogen infection and transmission. The characterization of the molecular function of SUB and the identification of tick proteins interacting with SUB may provide the basis for the discovery of novel antigens and for the rational design of novel anti-tick vaccines. In the present study, we used the yeast two-hybrid system (Y2H) as an unbiased approach to identify tick SUB-interacting proteins in an Ixodes ricinus cDNA library, and studied the possible role of SUB as a chromatin remodeler through direct interaction with histones. The Y2H screening identified Importin-α as a potential SUB-interacting protein, which was confirmed in vitro in a protein pull-down assay. The sub gene expression levels in tick midgut and fat body were significantly higher in unfed than fed female ticks, however, the importin-α expression levels did not vary between unfed and fed ticks but tended to be higher in the ovary when compared to those in other organs. The effect of importin-α RNAi was characterized in I. ricinus under artificial feeding conditions. Both sub and importin-α gene knockdown was observed in all tick tissues and, while tick weight was significantly lower in sub RNAi-treated ticks than in controls, importin-α RNAi did not affect tick feeding or oviposition, suggesting that SUB is able to exert its function in the absence of Importin-α. Furthermore, SUB was shown to physically interact with histone 4, which was corroborated by protein pull-down and western blot analysis. These results confirm that by interacting with numerous tick proteins, SUB is a key cofactor of the tick interactome and regulome. Further studies are needed to elucidate the nature of the SUB-Importin-α interaction and the biological processes and functional implications that this interaction may have.

The genus Anaplasma: drawing back the curtain on tick-pathogen interactions

Tick-borne illnesses pose a serious concern to human and veterinary health and their prevalence is on the rise. The interactions between ticks and the pathogens they carry are largely undefined. However, the genus Anaplasma, a group of tick-borne bacteria, has been instrumental in uncovering novel paradigms in tick biology. The emergence of sophisticated technologies and the convergence of entomology with microbiology, immunology, metabolism and systems biology has brought tick-Anaplasma interactions to the forefront of vector biology with broader implications for the infectious disease community. Here, we discuss the use of Anaplasma as an instrument for the elucidation of novel principles in arthropod-microbe interactions. We offer an outlook of the primary areas of study, outstanding questions and future research directions.

Control of tick infestations in wild roe deer (Capreolus capreolus) vaccinated with the Q38 Subolesin/Akirin chimera

Ticks (Acari: Ixodidae) are considered to be the most important vectors of disease-causing pathogens in domestic and wild animals, and emerging and re-emerging tick-borne diseases (TBD) exert an enormous impact on them. Wild ungulates are hosts for a wide variety of tick species and tick-borne pathogens that affect human and animal health. Consequently, the control of tick infestations and tick-borne pathogen prevalence is essential in some regions. Acaricides and animal management or culling have been used for the control of tick infestations and TBD, but tick vaccines constitute the best alternative to reduce the impact of acaricides on tick resistance and the environment. Previous results of controlled vaccination trials have shown that the Q38 Subolesin/Akirin chimera containing conserved protective epitopes could be a candidate universal antigen to control multiple tick species infestations. Thus, vaccination trials are necessary to validate these results under field conditions. In this study, we characterized the effect of Q38 vaccine on a wild population of European roe deer (Capreolus capreolus) in the Andalusian roe deer Reference Station (Junta de Andalucía, Cádiz, Spain). In this location, roe deer suffer especially severe parasitic conditions in some periods and commercial pesticides and ixodicides that are authorized to control ticks without specificity are frequently applied in the field, posing a threat to the environment. Animals vaccinated over a three-year period showed an antibody response to the vaccine antigen and a reduction in tick infestations by multiple species including Hyalomma marginatum, H. lusitanicum, Rhipicephalus bursa and Ixodes ricinus previously identified in roe deer, when compared to untreated controls. These results suggest the efficacy of Q38 for the control of tick infestations in wildlife.

The effect of silencing immunity related genes on longevity in a naturally occurring Anopheles arabiensis mosquito population from southwest Ethiopia

BACKGROUND

Vector control remains the most important tool to prevent malaria transmission. However, it is now severely constrained by the appearance of physiological and behavioral insecticide resistance. Therefore, the development of new vector control tools is warranted. Such tools could include immunization of blood hosts of vector mosquitoes with mosquito proteins involved in midgut homeostasis (anti-mosquito vaccines) or genetic engineering of mosquitoes that can drive population-wide knockout of genes producing such proteins to reduce mosquito lifespan and malaria transmission probability.

METHODS

To achieve this, candidate genes related to midgut homeostasis regulation need to be assessed for their effect on mosquito survival. Here, different such candidate genes were silenced through dsRNA injection in the naturally occurring Anopheles arabiensis mosquitoes and the effect on mosquito survival was evaluated.

RESULTS

Significantly higher mortality rates were observed in the mosquitoes silenced for FN3D1 (AARA003032), FN3D3 (AARA007751) and GPRGr9 (AARA003963) genes as compared to the control group injected with dsRNA against a non-related bacterial gene (LacZ). This observed difference in mortality rate between the candidate genes and the control disappeared when gene-silenced mosquitoes were treated with antibiotic mixtures, suggesting that gut microbiota play a key role in the observed reduction of mosquito survival.

CONCLUSIONS

We demonstrated that interference with the expression of the FN3D1, FN3D3 or GPRGr9 genes causes a significant reduction of the longevity of An. arabiensis mosquito in the wild.

Functional Evolution of Subolesin/Akirin

The Subolesin/Akirin constitutes a good model for the study of functional evolution because these proteins have been conserved throughout the metazoan and play a role in the regulation of different biological processes. Here, we investigated the evolutionary history of Subolesin/Akirin with recent results on their structure, protein-protein interactions and function in different species to provide insights into the functional evolution of these regulatory proteins, and their potential as vaccine antigens for the control of ectoparasite infestations and pathogen infection. The results suggest that Subolesin/Akirin evolved conserving not only its sequence and structure, but also its function and role in cell interactome and regulome in response to pathogen infection and other biological processes. This functional conservation provides a platform for further characterization of the function of these regulatory proteins, and how their evolution can meet species-specific demands. Furthermore, the conserved functional evolution of Subolesin/Akirin correlates with the protective capacity shown by these proteins in vaccine formulations for the control of different arthropod and pathogen species. These results encourage further research to characterize the structure and function of these proteins, and to develop new vaccine formulations by combining Subolesin/Akirin with interacting proteins for the control of multiple ectoparasite infestations and pathogen infection.

Characterization of the Akirin Gene and Its Role in the NF-κB Signaling Pathway of Sogatella furcifera

Akirin is an essential nuclear protein involved in the regulation of NF-κB signaling pathway. In most invertebrates, Akirin regulates NF-κB-related Imd and Toll pathways, however, in Drosophila, it only controls the Imd pathway, whereas its role in NF-κB signaling pathway in other insect species is unclear. In the present study, we used white-backed planthopper Sogatella furcifera as a model to investigate the functional activity of Akirin in insects. The sequence of Akirin cDNA was extracted from transcriptome database of S. furcifera; it contained a 585 bp open reading frame (ORF) encoding a putative protein of 194 amino acids. S. furcifera Akirin (SfAkirin) had a molecular weight of about 21.69 kDa and a theoretical pI of 8.66 and included a nuclear localization signal (NLS) of five amino acid residues at the N-terminal region. Evolutionary analysis showed that SfAkirin was evolutionary closer to Akirins of such relatively distant species as crustaceans than to those of some insect orders like Diptera and Hymenoptera. Tissue-specific expression analysis showed that the SfAkirin gene was expressed in all examined tissues, with the highest expression levels detected in the testis, followed by the ovary, whereas the lowest expression was found in the head. Real-time quantitative PCR analysis showed that SfAkirin mRNA was strongly induced in response to injection of heat-inactivated Escherichia coli and Bacillus subtilis, whereas SfAkirin silencing by RNA interference significantly reduced the expression of NF-κB dependent transcription factors Dorsal and Relish after B. subtilis and E. coli challenge, respectively. Our results suggest that SfAkirin may control the immune response of S. furcifera against bacterial infection via both Imd and Toll signaling pathways.

Differential expression analysis for subolesin in Rhipicephalus microplus infected with Anaplasma marginale

Rhipicephalus microplus (formerly Boophilus microplus) ticks are potential vectors of several pathogens of livestock especially in tropical and subtropical regions where may have substantial effects on economic development. Among tick-borne pathogens, Anaplasma marginale is considered one of the most important in domestic and wild ruminants worldwide. Different molecular mechanisms have been employed by both ticks and these intracellular pathogens, in order to be able to adapt and survive. Subolesin, originally called 4D8, is an evolutionarily well-preserved protein among ixodid tick species. This new antigen was found to be protective against tick infestations when used as a vaccine, as it has an essential role in tick blood digestion, development and infection of host cells by A. marginale. Recent studies have demonstrated that infection of both tick and vertebrate host cells with this microorganism changed gene expression. Therefore, the main objective of this study was to investigate subolesin expression in uninfected and A. marginale-infected R. microplus salivary glands by real-time reverse transcriptase (RT)-PCR. To analyze the differential expression of the recombinant protein subolesin, the gene was previously expressed from ticks infected with A. marginale. Results from this study revealed that, the expression of subolesin was significantly higher in salivary glands of infected R. microplus in comparison to uninfected ones.

Heat-inactivated Mycobacterium bovis protects zebrafish against mycobacteriosis

Control of mycobacterial infection constitutes a priority for human and animal health worldwide. However, effective vaccines are needed for the control of human and animal tuberculosis (TB). Adult zebrafish have become a useful model for studying the pathophysiology of mycobacterial infection and for the development of novel interventions for TB control and prevention. Recently, parenteral and oral immunization with the heat-inactivated Mycobacterium bovis vaccine (M. bovis IV) protected wild boar against TB. The objectives of this study were to provide additional support for the role of M. bovis IV in TB control using the zebrafish model and to conduct the first trial with this vaccine for the control of fish mycobacteriosis. The results showed that M. bovis IV protected zebrafish against mycobacteriosis caused by low and high infection doses of Mycobacterium marinum and provided evidence suggesting that the protective mechanism elicited by M. bovis IV in zebrafish as in other species is based on the activation of the innate immune response through the C3 pathway, with a role for the regulatory protein Akr2 in this process. These results encourage the use of M. bovis IV for TB control in different species.

NF‑κB is a key modulator in the signaling pathway of Borrelia burgdorferi BmpA‑induced inflammatory chemokines in murine microglia BV2 cells

Lyme disease, caused by the bacterial spirochete Borrelia burgdorferi, is a tick‑borne zoonosis. Lyme neuroborreliosis is a principal manifestation of Lyme disease and its pathogenesis remains incompletely understood. Recent studies have demonstrated that Borrelia burgdorferi lipoproteins caused similar inflammatory effects as exhibited in Lyme neuroborreliosis. Basic membrane protein A (BmpA) is one of the dominant lipoproteins in the Borrelia burgdorferi membrane. In addition, nuclear factor κ‑B (NF‑κB) modulates the regulation of gene transcription associated with immunity and inflammation; however, in unstimulated cells, NF‑κB is combined with the inhibitor of NF‑κB (IκB‑β). Therefore, it was hypothesized that NF‑κB may be associated with BmpA‑induced inflammation and the occurrence of Lyme neuroborreliosis. Therefore, the aim of the present study was to investigate the role that NF‑κB serves in the signaling pathway of rBmpA‑induced inflammatory chemokines. The present study measured the expression levels of NF‑κB, IκB‑β and inflammatory chemokines following recombinant BmpA (rBmpA) stimulation of murine microglia BV2 cells. Following stimulation with rBmpA, concentrations of pro‑inflammatory cytokines including C‑X‑C motif chemokine 2, C‑C motif chemokine (CCL) 5 and CCL22 were determined by ELISA analysis. Reverse transcription‑quantitative polymerase chain reaction and western blotting were used to detect the expression levels of NF‑κB p65 and IκB‑β. The data demonstrated that concentrations of these chemokines in cell supernatants increased significantly following rBmpA stimulation. NF‑κB was overexpressed, but IκB‑β expression was significantly decreased. In conclusion, these results suggested that NF‑κB serves an important stimulatory role in the signaling pathway of rBmpA‑induced inflammatory chemokines in BV2 cells.

The Essential Role of Tick Salivary Glands and Saliva in Tick Feeding and Pathogen Transmission

As long-term pool feeders, ticks have developed myriad strategies to remain discreetly but solidly attached to their hosts for the duration of their blood meal. The critical biological material that dampens host defenses and facilitates the flow of blood-thus assuring adequate feeding-is tick saliva. Saliva exhibits cytolytic, vasodilator, anticoagulant, anti-inflammatory, and immunosuppressive activity. This essential fluid is secreted by the salivary glands, which also mediate several other biological functions, including secretion of cement and hygroscopic components, as well as the watery component of blood as regards hard ticks. When salivary glands are invaded by tick-borne pathogens, pathogens may be transmitted via saliva, which is injected alternately with blood uptake during the tick bite. Both salivary glands and saliva thus play a key role in transmission of pathogenic microorganisms to vertebrate hosts. During their long co-evolution with ticks and vertebrate hosts, microorganisms have indeed developed various strategies to exploit tick salivary molecules to ensure both acquisition by ticks and transmission, local infection and systemic dissemination within the vertebrate host.

Tick-Pathogen Interactions and Vector Competence: Identification of Molecular Drivers for Tick-Borne Diseases

Ticks and the pathogens they transmit constitute a growing burden for human and animal health worldwide. Vector competence is a component of vectorial capacity and depends on genetic determinants affecting the ability of a vector to transmit a pathogen. These determinants affect traits such as tick-host-pathogen and susceptibility to pathogen infection. Therefore, the elucidation of the mechanisms involved in tick-pathogen interactions that affect vector competence is essential for the identification of molecular drivers for tick-borne diseases. In this review, we provide a comprehensive overview of tick-pathogen molecular interactions for bacteria, viruses, and protozoa affecting human and animal health. Additionally, the impact of tick microbiome on these interactions was considered. Results show that different pathogens evolved similar strategies such as manipulation of the immune response to infect vectors and facilitate multiplication and transmission. Furthermore, some of these strategies may be used by pathogens to infect both tick and mammalian hosts. Identification of interactions that promote tick survival, spread, and pathogen transmission provides the opportunity to disrupt these interactions and lead to a reduction in tick burden and the prevalence of tick-borne diseases. Targeting some of the similar mechanisms used by the pathogens for infection and transmission by ticks may assist in development of preventative strategies against multiple tick-borne diseases.

Strategies for new and improved vaccines against ticks and tick-borne diseases

Ticks infest a variety of animal species and transmit pathogens causing disease in both humans and animals worldwide. Tick-host-pathogen interactions have evolved through dynamic processes that accommodated the genetic traits of the hosts, pathogens transmitted and the vector tick species that mediate their development and survival. New approaches for tick control are dependent on defining molecular interactions between hosts, ticks and pathogens to allow for discovery of key molecules that could be tested in vaccines or new generation therapeutics for intervention of tick-pathogen cycles. Currently, tick vaccines constitute an effective and environmentally sound approach for the control of ticks and the transmission of the associated tick-borne diseases. New candidate protective antigens will most likely be identified by focusing on proteins with relevant biological function in the feeding, reproduction, development, immune response, subversion of host immunity of the tick vector and/or molecules vital for pathogen infection and transmission. This review addresses different approaches and strategies used for the discovery of protective antigens, including focusing on relevant tick biological functions and proteins, reverse genetics, vaccinomics and tick protein evolution and interactomics. New and improved tick vaccines will most likely contain multiple antigens to control tick infestations and pathogen infection and transmission.

Control of Ixodes ricinus and Dermacentor reticulatus tick infestations in rabbits vaccinated with the Q38 Subolesin/Akirin chimera

Diseases transmitted by ticks greatly impact human and animal health and their control is important for the eradication of tick-borne diseases. Vaccination is an environmentally friendly alternative for tick control. Recent results have suggested that Subolesin/Akirin (SUB/AKR) are good candidate antigens for the control of arthropod vector infestations. Here, we describe the effect of vaccination with the Q38 chimera containing SUB/AKR conserved protective epitopes on Ixodes ricinus and Dermacentor reticulatus tick larval mortality, feeding and molting. We demonstrated that Q38 vaccination had an efficacy of 99.9% and 46.4% on the control of I. ricinus and D. reticulatus larvae by considering the cumulative effect on reducing tick survival and molting. The effect of the Q38 vaccine on larval feeding and molting is essential to reduce tick infestations and supports that Q38 might be a candidate universal antigen for the control of multiple tick species that can infest the same host.

RNA interference and the vaccine effect of a subolesin homolog from the tick Rhipicephalus haemaphysaloides

Subolesin is a well-characterized protective antigen in many ticks and, thus, it is potentially useful in the development of a broad-spectrum vaccine or an autocidal gene silencing strategy to control tick infestations. A subolesin homolog was cloned from the tick Rhipicephalus haemaphysaloides, which is widespread in China, by rapid amplification of complementary DNA (cDNA) ends. Its full-length cDNA was 1386 base pairs (bp), containing a 483 bp open reading frame with a predicted molecular mass of 18.7 kilodaltons and an isoelectric point of 9.26. The subolesin protein had a typical nuclear localization signal in its amino-terminus. The full-length cDNA of R. haemaphysaloides showed 52 and 80% identities to those from Ixodes scapularis and R. microplus, respectively, whereas amino acid sequence alignments showed 80 and 97% identities, respectively. Native subolesin was recognized in the unfed tick midgut by an antibody against recombinant subolesin. Transcriptional analysis showed that subolesin was expressed in the tick's four developmental stages and in all of the tissues examined, except for the synganglion. The pathogen Babesia microti induced the subolesin transcript by fourfold. Subolesin gene silencing by RNA interference significantly decreased the larval engorgement rate, the attachment rate and body weight of engorged nymphs, and the body weight and attachment and engorgement rates of adults, as well as the egg weight per female tick. Vaccinating mice and rabbits with recombinant subolesin induced a significant protective effect, resulting in a reduction of blood feeding and oviposition. These results encourage further studies of using subolesin to control tick infestations in China.

Anaplasma phagocytophilum Uses Common Strategies for Infection of Ticks and Vertebrate Hosts

The tick-borne rickettsial pathogen Anaplasma phagocytophilum develops within membrane-bound inclusions in the host cell cytoplasm. This pathogen has evolved with its tick and vertebrate hosts through dynamic processes involving genetic traits of the pathogen and hosts that collectively mediate pathogen infection, development, persistence, and survival. Herein, we challenge the evidence of tick-host-pathogen coevolution by hypothesizing that A. phagocytophilum utilizes common molecular mechanisms for infection in both vertebrate and tick cells, including remodeling of the cytoskeleton, inhibition of cell apoptosis, and manipulation of the immune response. The discovery of these common mechanisms provides evidence that a control strategy could be developed targeted at both vertebrate and tick hosts for more complete control of A. phagocytophilum and its associated diseases.

Insights into the development of Ixodes scapularis: a resource for research on a medically important tick species

Ticks (Acari: Ixodida) are arthropod ectoparasites dependent on a bloodmeal from a vertebrate host at each developmental stage for completion of their life cycle. This tick feeding cycle impacts animal health by causing damage to hides, secondary infections, immune reactions and diseases caused by transmission of pathogens. The genus Ixodes includes several medically important species that vector diseases, including granulocytic anaplasmosis and Lyme disease. I. scapularis, commonly called the black-legged or deer tick, is a medically-important tick species in North America and therefore was the first tick genome to be sequenced, thus serving as an important resource for tick research. This Primer focuses on the normal developmental cycle and laboratory rearing of I. scapularis. Definition of normal morphology, along with a consistent source of laboratory-reared I. scapularis, are fundamental for all aspects of future research, especially the effects of genetic manipulation and the evaluation of tick vaccine efficacy. Recent research important for the advancement of tick research, namely the development of tick cell culture systems for study of ticks and tick-borne pathogens, RNA interference for genetic manipulation of ticks and discovery of candidate antigens for development of tick vaccines, are briefly presented along with areas to target for future research.

Integrated Metabolomics, Transcriptomics and Proteomics Identifies Metabolic Pathways Affected by Anaplasma phagocytophilum Infection in Tick Cells

Anaplasma phagocytophilum is an emerging zoonotic pathogen that causes human granulocytic anaplasmosis. These intracellular bacteria establish infection by affecting cell function in both the vertebrate host and the tick vector, Ixodes scapularis. Previous studies have characterized the tick transcriptome and proteome in response to A. phagocytophilum infection. However, in the postgenomic era, the integration of omics datasets through a systems biology approach allows network-based analyses to describe the complexity and functionality of biological systems such as host-pathogen interactions and the discovery of new targets for prevention and control of infectious diseases. This study reports the first systems biology integration of metabolomics, transcriptomics, and proteomics data to characterize essential metabolic pathways involved in the tick response to A. phagocytophilum infection. The ISE6 tick cells used in this study constitute a model for hemocytes involved in pathogen infection and immune response. The results showed that infection affected protein processing in endoplasmic reticulum and glucose metabolic pathways in tick cells. These results supported tick-Anaplasma co-evolution by providing new evidence of how tick cells limit pathogen infection, while the pathogen benefits from the tick cell response to establish infection. Additionally, ticks benefit from A. phagocytophilum infection by increasing survival while pathogens guarantee transmission. The results suggested that A. phagocytophilum induces protein misfolding to limit the tick cell response and facilitate infection but requires protein degradation to prevent ER stress and cell apoptosis to survive in infected cells. Additionally, A. phagocytophilum may benefit from the tick cell's ability to limit bacterial infection through PEPCK inhibition leading to decreased glucose metabolism, which also results in the inhibition of cell apoptosis that increases infection of tick cells. These results support the use of this experimental approach to systematically identify cell pathways and molecular mechanisms involved in tick-pathogen interactions. Data are available via ProteomeXchange with identifier PXD002181.

Identification and Characterization of Anaplasma phagocytophilum Proteins Involved in Infection of the Tick Vector, Ixodes scapularis

Anaplasma phagocytophilum is an emerging zoonotic pathogen transmitted by Ixodes scapularis that causes human granulocytic anaplasmosis. Here, a high throughput quantitative proteomics approach was used to characterize A. phagocytophilum proteome during rickettsial multiplication and identify proteins involved in infection of the tick vector, I. scapularis. The first step in this research was focused on tick cells infected with A. phagocytophilum and sampled at two time points containing 10–15% and 65–71% infected cells, respectively to identify key bacterial proteins over-represented in high percentage infected cells. The second step was focused on adult female tick guts and salivary glands infected with A. phagocytophilum to compare in vitro results with those occurring during bacterial infection in vivo. The results showed differences in the proteome of A. phagocytophilum in infected ticks with higher impact on protein synthesis and processing than on bacterial replication in tick salivary glands. These results correlated well with the developmental cycle of A. phagocytophilum, in which cells convert from an intracellular reticulated, replicative form to the nondividing infectious dense-core form. The analysis of A. phagocytophilum differentially represented proteins identified stress response (GroEL, HSP70) and surface (MSP4) proteins that were over-represented in high percentage infected tick cells and salivary glands when compared to low percentage infected cells and guts, respectively. The results demonstrated that MSP4, GroEL and HSP70 interact and bind to tick cells, thus playing a role in rickettsia-tick interactions. The most important finding of these studies is the increase in the level of certain bacterial stress response and surface proteins in A. phagocytophilum-infected tick cells and salivary glands with functional implication in tick-pathogen interactions. These results gave a new dimension to the role of these stress response and surface proteins during A. phagocytophilum infection in ticks. Characterization of Anaplasma proteome contributes information on host-pathogen interactions and provides targets for development of novel control strategies for pathogen infection and transmission.

Discovery, adaptation and transcriptional activity of two tick promoters: Construction of a dual luciferase reporter system for optimization of RNA interference in rhipicephalus (boophilus) microplus cell lines

Dual luciferase reporter systems are valuable tools for functional genomic studies, but have not previously been developed for use in tick cell culture. We evaluated expression of available luciferase constructs in tick cell cultures derived from Rhipicephalus (Boophilus) microplus, an important vector of bovine babesiosis and anaplasmosis. Commercial promoters were evaluated for transcriptional activity driving luciferase expression in the tick cell lines. The human phosphoglycerate kinase (PGK) promoter resulted in detectable firefly luciferase activity within 2 days post-transfection of the R. microplus cell line BME26, with maximal activity at 5 days post-transfection. Several other promoters were weaker or inactive in the tick cells, prompting identification and assessment of transcriptional activity of the homologous ribosomal protein L4 (rpL4, GenBank accession no.: KM516205) and elongation factor 1α (EF-1α, GenBank accession no.: KM516204) promoters cloned from R. microplus. Evaluation of luciferase expression driven by various promoters in tick cell culture resulted in selection of the R. microplus rpL4 promoter and the human PGK promoter driving transcription of sequences encoding modified firefly and NanoLuc® luciferases for construction of a dual luciferase reporter system for use in tick cell culture.

An Ixodes scapularis cell line with a predominantly neuron-like phenotype

The Ixodes scapularis embryo-derived cell line ISE6 is the most widely utilized tick-derived cell line due to its susceptibility to a wide variety of tick- and non-tick-vectored pathogens. Little is known about its tissue origin or biological background. Protein expression of ISE6 cells was compared with that of another I. scapularis-derived cell line, IDE12, and dissected tick synganglia. Results demonstrated the presence of a neuronal marker protein, type 3 β-tubulin, in all three samples, as well as other shared and unique neuronal and immune response-associated proteins. Of neuronal proteins shared between the two cell lines, ISE6 expressed several in significantly greater quantities than IDE12. Stimulation of ISE6 cells by in vivo exposure to the hemocoel environment in unfed larval and molting nymphal ticks, but not unfed nymphal ticks, resulted in the development of neuron-like morphologic characteristics in the implanted cells.

Systems biology of tissue-specific response to Anaplasma phagocytophilum reveals differentiated apoptosis in the tick vector Ixodes scapularis

Anaplasma phagocytophilum is an emerging pathogen that causes human granulocytic anaplasmosis. Infection with this zoonotic pathogen affects cell function in both vertebrate host and the tick vector, Ixodes scapularis. Global tissue-specific response and apoptosis signaling pathways were characterized in I. scapularis nymphs and adult female midguts and salivary glands infected with A. phagocytophilum using a systems biology approach combining transcriptomics and proteomics. Apoptosis was selected for pathway-focused analysis due to its role in bacterial infection of tick cells. The results showed tissue-specific differences in tick response to infection and revealed differentiated regulation of apoptosis pathways. The impact of bacterial infection was more pronounced in tick nymphs and midguts than in salivary glands, probably reflecting bacterial developmental cycle. All apoptosis pathways described in other organisms were identified in I. scapularis, except for the absence of the Perforin ortholog. Functional characterization using RNA interference showed that Porin knockdown significantly increases tick colonization by A. phagocytophilum. Infection with A. phagocytophilum produced complex tissue-specific alterations in transcript and protein levels. In tick nymphs, the results suggested a possible effect of bacterial infection on the inhibition of tick immune response. In tick midguts, the results suggested that A. phagocytophilum infection inhibited cell apoptosis to facilitate and establish infection through up-regulation of the JAK/STAT pathway. Bacterial infection inhibited the intrinsic apoptosis pathway in tick salivary glands by down-regulating Porin expression that resulted in the inhibition of Cytochrome c release as the anti-apoptotic mechanism to facilitate bacterial infection. However, tick salivary glands may promote apoptosis to limit bacterial infection through induction of the extrinsic apoptosis pathway. These dynamic changes in response to A. phagocytophilum in I. scapularis tissue-specific transcriptome and proteome demonstrated the complexity of the tick response to infection and will contribute to characterize gene regulation in ticks.

The continuous human exploitation of environmental resources and the increase in human outdoor activities, which have allowed for the contact with arthropod vectors normally present in the field, has promoted the emergence and resurgence of vector-borne pathogens. Among these, Anaplasma phagocytophilum is an emerging bacterial pathogen transmitted to humans and other vertebrate hosts by ticks as they take a blood meal that causes human granulocytic anaplasmosis in the United States, Europe and Asia, with increasing numbers of affected people every year. Tick response to pathogen infection has been only partially characterized. In this study, global tissue-specific response and apoptosis signaling pathways were characterized in tick nymphs and adult female midguts and salivary glands infected with A. phagocytophilum using a systems biology approach combining transcriptomics and proteomics. The results demonstrated dramatic and complex tissue-specific response to A. phagocytophilum in the tick vector Ixodes scapularis, which reflected pathogen developmental cycle and the impact on tick apoptosis pathways. These dynamic changes in response to A. phagocytophilum in I. scapularis tissue-specific transcriptome and proteome demonstrated the complexity of the tick response to infection and contributes information on tick-pathogen interactions and for development of novel control strategies for pathogen infection and transmission.

Identification of protective linear B-cell epitopes on the subolesin/akirin orthologues of Ornithodoros spp. soft ticks

Subolesin/akirin is a protective antigen that is highly conserved across hematophagous vector species and is therefore potentially useful for the development of a universal vaccine for vector control, including soft ticks. Recent results have shown that in Ornithodoros erraticus and O. moubata soft ticks, RNAi-mediated subolesin gene knockdown inhibits tick oviposition and fertility by more than 90%; however, vaccination with recombinant subolesins resulted in remarkably low protective efficacies (5-24.5% reduction in oviposition). Here we report that vaccination with subolesin recombinants induces non-protective antibodies mainly directed against immunodominant linear B-cell epitopes located on highly structured regions of the subolesin protein, probably unrelated to its biological activity, while leaving the unstructured/disordered regions unrecognized. Accordingly, for a new vaccine trial we designed four synthetic peptides (OE1, OE2, OM1 and OM2) from the unrecognized/disordered regions of the Ornithodoros subolesin sequences and coupled them to keyhole limpet haemocyanin (KLH). These KLH-peptide conjugates induced the synthesis of antibodies that recognized linear B-cell epitopes located on the unstructured loops of the subolesin protein and provided up to 70.1% and 83.1% vaccine efficacies in O. erraticus and O. moubata, respectively. These results show that the protective effect of subolesin-based vaccines is highly dependent on the particular epitope recognized by antibodies on the subolesin sequence and strongly suggest that the biological activity of subolesin is exerted through its unstructured regions. The results reported here contribute to our understanding of the mechanism of protection of subolesin-based vaccines and reveal novel protective peptides that could be included among the array of candidate antigens useful for developing anti-vector vaccines based on subolesin/akirin.

Mosquito Akirin as a potential antigen for malaria control

Background

The control of vector-borne diseases is important to improve human and animal health worldwide. Malaria is one of the world’s deadliest diseases and is caused by protozoan parasites of the genus Plasmodium, which are transmitted by Anopheles spp. mosquitoes. Recent evidences using Subolesin (SUB) and Akirin (AKR) vaccines showed a reduction in the survival and/or fertility of blood-sucking ectoparasite vectors and the infection with vector-borne pathogens. These experiments suggested the possibility of using AKR for malaria control.

Methods

The role of AKR on Plasmodium berghei infection and on the fitness and reproduction of the main malaria vector, Anopheles gambiae was characterized by evaluating the effect of akr gene knockdown or vaccination with recombinant mosquito AKR on parasite infection levels, fertility and mortality of female mosquitoes.

Results

Gene knockdown by RNA interference in mosquitoes suggested a role for akr in mosquito survival and fertility. Vaccination with recombinant Aedes albopictus AKR reduced parasite infection in mosquitoes fed on immunized mice when compared to controls.

Conclusions

These results showed that recombinant AKR could be used to develop vaccines for malaria control. If effective, AKR-based vaccines could be used to immunize wildlife reservoir hosts and/or humans to reduce the risk of pathogen transmission. However, these vaccines need to be evaluated under field conditions to characterize their effect on vector populations and pathogen infection and transmission.

Studies of Anaplasma phagocytophilum in sheep experimentally infected with the human NY-18 isolate: characterization of tick feeding sites

Anaplasma phagocytophilum, transmitted by ticks of the genus Ixodes, was first described in Scotland as the agent of tick-borne fever in sheep and more recently as the cause of human granulocytic anaplasmosis in the U.S. and Europe. We previously reported sheep as an experimental host for the human NY-18 isolate of A. phagocytophilum. While clinical signs were not observed and infected granulocytes were not seen in stained blood smears, these sheep served as a good host for infection of ticks. In this research we characterized tick feeding sites to better understand tick/host/pathogen interactions. Ixodes scapularis adults were allowed to feed for 2 and 4 days on experimentally infected sheep, after which biopsies were taken beneath tick feeding sites for histopathology, PCR and immunohistochemistry (IHC) studies. In addition, the expression of selected immune response genes was studied in blood and feeding site biopsies. While necrosis was too advanced in 4-day biopsies for accurate cell counts, higher numbers of eosinophils and neutrophils were found in 2-day biopsies from infected sheep as compared with the uninfected controls. An unexpected result was the documentation of higher dermal inflammation in infected sheep at sites without ticks. A. phagocytophilum infected granulocytes were localized by immunohistochemistry (IHC) in skin biopsies using rabbit antibodies against the recombinant A. phagocytophilum major surface protein 4 as the primary antibody for indirect peroxidase-anti-peroxidase and fluorescent antibody IHC. These infected cells are likely to be the source of infection for ticks. Sheep therefore served as good hosts for studying host/pathogen/tick interactions of this human strain of A. phagocytophilum, and provided a means of producing infected ticks for future studies on tick/pathogen developmental and transmission cycles.

Antiviral responses of arthropod vectors: an update on recent advances

Arthropod vectors, such as mosquitoes, ticks, biting midges and sand flies, transmit many viruses that can cause outbreaks of disease in humans and animals around the world. Arthropod vector species are invading new areas due to globalisation and environmental changes, and contact between exotic animal species, humans and arthropod vectors is increasing, bringing with it the regular emergence of new arboviruses. For future strategies to control arbovirus transmission, it is important to improve our understanding of virus-vector interactions. In the last decade knowledge of arthropod antiviral immunity has increased rapidly. RNAi has been proposed as the most important antiviral response in mosquitoes and it is likely to be the most important antiviral response in all arthropods. However, other newly-discovered antiviral strategies such as melanisation and the link between RNAi and the JAK/STAT pathway via the cytokine Vago have been characterised in the last few years. This review aims to summarise the most important and most recent advances made in arthropod antiviral immunity.

Patent Highlights

A snapshot of recent key developments in the patent literature of relevance to the advancement of pharmaceutical and medical R&D.

Subolesin: a candidate vaccine antigen for the control of cattle tick infestations in Indian situation

Identification of cross-protective tick vaccine antigens is a challenging area of veterinary research. To address this challenge, a recently identified candidate tick protective antigen, Subolesin (SUB), was targeted in this research. The conservation of subolesin ortholog of Hyalomma anatolicum and Rhipicephalus (Boophilus) microplus across different Indian strains was 98.1-99.4% (within species), while at the amino acid level SUB sequence homology was ≥53.2% (between tick species). Recombinant R. (B.) microplus SUB (rBmSu) was produced in Escherichia coli and characterized. Cross-bred cattle male calves (N=10) were immunized with three doses of 100 μg each of the rBmSu emulsified in 10% Montanide 888 at monthly intervals on days 0, 30 and 60. The control group was injected with PBS in 10% Montanide 888. For the first tick challenge, calves were infested with larvae of R. (B.) microplus generated from 100mg eggs 2 weeks after last immunization (day 75). The immunization resulted in 16.3%, 8.0%, 9.4%, and 26.1% reduction in female tick numbers (DT), weight (DW), oviposition (DO) and egg fertility (DF), respectively, when compared to controls. In the subsequent challenge on day 105, DT, DW, DO and DF were reduced by 9.0%, 4.1%, 8.6%, and 24.2%, respectively, when compared to controls. The vaccine efficacy (E) was equal to 44.0% and 37.2% after the first and second challenges, respectively. The results showed a positive correlation between antibody titers for both total IgG and IgG1 and E in the second but not in the first tick challenge. These results suggested the possibility of developing a SUB-based vaccine for control of cattle tick infestations under Indian conditions.

Tick capillary feeding for the study of proteins involved in tick-pathogen interactions as potential antigens for the control of tick infestation and pathogen infection

Background

Ticks represent a significant health risk to animals and humans due to the variety of pathogens they can transmit during feeding. The traditional use of chemicals to control ticks has serious drawbacks, including the selection of acaricide-resistant ticks and environmental contamination with chemical residues. Vaccination with the tick midgut antigen BM86 was shown to be a good alternative for cattle tick control. However, results vary considerably between tick species and geographic location. Therefore, new antigens are required for the development of vaccines controlling both tick infestations and pathogen infection/transmission. Tick proteins involved in tick-pathogen interactions may provide good candidate protective antigens for these vaccines, but appropriate screening procedures are needed to select the best candidates.

Methods

In this study, we selected proteins involved in tick-Anaplasma (Subolesin and SILK) and tick-Babesia (TROSPA) interactions and used in vitro capillary feeding to characterize their potential as antigens for the control of cattle tick infestations and infection with Anaplasma marginale and Babesia bigemina. Purified rabbit polyclonal antibodies were generated against recombinant SUB, SILK and TROSPA and added to uninfected or infected bovine blood to capillary-feed female Rhipicephalus (Boophilus) microplus ticks. Tick weight, oviposition and pathogen DNA levels were determined in treated and control ticks.

Results

The specificity of purified rabbit polyclonal antibodies against tick recombinant proteins was confirmed by Western blot and against native proteins in tick cell lines and tick tissues using immunofluorescence. Capillary-fed ticks ingested antibodies added to the blood meal and the effect of these antibodies on tick weight and oviposition was shown. However, no effect was observed on pathogen DNA levels.

Conclusions

These results highlighted the advantages and some of the disadvantages of in vitro tick capillary feeding for the characterization of candidate tick protective antigens. While an effect on tick weight and oviposition was observed, the effect on pathogen levels was not evident probably due to high tick-to-tick variations among other factors. Nevertheless, these results together with previous results of RNA interference functional studies suggest that these proteins are good candidate vaccine antigens for the control of R. microplus infestations and infection with A. marginale and B. bigemina.

Vaccination with proteins involved in tick-pathogen interactions reduces vector infestations and pathogen infection

Tick-borne pathogens cause diseases that greatly impact animal health and production worldwide. The ultimate goal of tick vaccines is to protect against tick-borne diseases through the control of vector infestations and reducing pathogen infection and transmission. Tick genetic traits are involved in vector-pathogen interactions and some of these molecules such as Subolesin (SUB) have been shown to protect against vector infestations and pathogen infection. Based on these premises, herein we characterized the efficacy of cattle vaccination with tick proteins involved in vector-pathogen interactions, TROSPA, SILK, and Q38 for the control of cattle tick, Rhipicephalus (Boophilus) microplus infestations and infection with Anaplasma marginale and Babesia bigemina. SUB and adjuvant/saline placebo were used as positive and negative controls, respectively. The results showed that vaccination with Q38, SILK and SUB reduced tick infestations and oviposition with vaccine efficacies of 75% (Q38), 62% (SILK) and 60% (SUB) with respect to ticks fed on placebo control cattle. Vaccination with TROSPA did not have a significant effect on any of the tick parameters analyzed. The results also showed that vaccination with Q38, TROSPA and SUB reduced B. bigemina DNA levels in ticks while vaccination with SILK and SUB resulted in lower A. marginale DNA levels when compared to ticks fed on placebo control cattle. The positive correlation between antigen-specific antibody titers and reduction of tick infestations and pathogen infection strongly suggested that the effect of the vaccine was the result of the antibody response in vaccinated cattle. Vaccination and co-infection with A. marginale and B. bigemina also affected the expression of genes encoding for vaccine antigens in ticks fed on cattle. These results showed that vaccines using tick proteins involved in vector-pathogen interactions could be used for the dual control of tick infestations and pathogen infection.

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.