The vector competence of blood-feeding arthropods is influenced by the interaction between pathogens and the immune system of the vector. The Toll and IMD (immune deficiency) signaling pathways play a key role in the regulation of innate immunity in both the Drosophila model and blood-feeding insects. However, in ticks (chelicerates), immune determination for pathogen acquisition and transmission has not yet been fully explored. Here, we have mapped homologs of insect Toll and IMD pathways in the European tick Ixodes ricinus, an important vector of human and animal diseases. We show that most genes of the Toll pathway are well conserved, whereas the IMD pathway has been greatly reduced. We therefore investigated the functions of the individual components of the tick Toll pathway and found that, unlike in Drosophila, it was specifically activated by Gram-negative bacteria. The activation of pathway induced the expression of defensin (defIR), the first identified downstream effector gene of the tick Toll pathway. Borrelia, an atypical bacterium and causative agent of Lyme borreliosis, bypassed Toll-mediated recognition in I. ricinus and also resisted systemic effector molecules when the Toll pathway was activated by silencing its repressor cactus via RNA interference. Babesia, an apicomplexan parasite, also avoided Toll-mediated recognition. Strikingly, unlike Borrelia, the number of Babesia parasites reaching the salivary glands during tick infection was significantly reduced by knocking down cactus. The simultaneous silencing of cactus and dorsal resulted in greater infections and underscored the importance of tick immunity in regulating parasite infections in these important disease vectors.

• MeSH
• Babesia microti * immunology   MeSH
• Babesiosis immunology   parasitology   MeSH
• Ixodes * parasitology   immunology   MeSH
• Immunity, Innate MeSH
• Signal Transduction * MeSH
• Toll-Like Receptors * metabolism   immunology   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Toll-Like Receptors * MeSH

Ticks are ectoparasitic arthropods that necessarily feed on the blood of their vertebrate hosts. The success of blood acquisition depends on the pharmacological properties of tick saliva, which is injected into the host during tick feeding. Saliva is also used as a vehicle by several types of pathogens to be transmitted to the host, making ticks versatile vectors of several diseases for humans and other animals. When a tick feeds on an infected host, the pathogen reaches the gut of the tick and must migrate to its salivary glands via hemolymph to be successfully transmitted to a subsequent host during the next stage of feeding. In addition, some pathogens can colonize the ovaries of the tick and be transovarially transmitted to progeny. The tick immune system, as well as the immune system of other invertebrates, is more rudimentary than the immune system of vertebrates, presenting only innate immune responses. Although simpler, the large number of tick species evidences the efficiency of their immune system. The factors of their immune system act in each tick organ that interacts with pathogens; therefore, these factors are potential targets for the development of new strategies for the control of ticks and tick-borne diseases. The objective of this review is to present the prevailing knowledge on the tick immune system and to discuss the challenges of studying tick immunity, especially regarding the gaps and interconnections. To this end, we use a comparative approach of the tick immune system with the immune system of other invertebrates, focusing on various components of humoral and cellular immunity, such as signaling pathways, antimicrobial peptides, redox metabolism, complement-like molecules and regulated cell death. In addition, the role of tick microbiota in vector competence is also discussed.

• Keywords
• cell-mediated immunity, immune signaling pathway, immune system, microbiota, tick-borne pathogen,
• MeSH
• Immunity, Cellular * MeSH
• Immunity, Humoral * MeSH
• Host-Parasite Interactions MeSH
• Ticks immunology   metabolism   MeSH
• Humans MeSH
• Tick-Borne Diseases immunology   metabolism   transmission   MeSH
• Salivary Glands immunology   metabolism   MeSH
• Saliva immunology   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH

Lyme borreliosis is an emerging tick-borne disease caused by spirochetes Borrelia burgdorferi sensu lato. In Europe, Lyme borreliosis is predominantly caused by Borrelia afzelii and transmitted by Ixodes ricinus. Although Borrelia behavior throughout tick development is quite well documented, specific molecular interactions between Borrelia and the tick have not been satisfactorily examined. Here, we present the first transcriptomic study focused on the expression of tick midgut genes regulated by Borrelia. By using massive analysis of cDNA ends (MACE), we searched for tick transcripts expressed differentially in the midgut of unfed, 24h-fed, and fully fed I. ricinus nymphs infected with B. afzelii. In total, we identified 553 upregulated and 530 downregulated tick genes and demonstrated that B. afzelii interacts intensively with the tick. Technical and biological validations confirmed the accuracy of the transcriptome. The expression of five validated tick genes was silenced by RNA interference. Silencing of the uncharacterized protein (GXP_Contig_30818) delayed the infection progress and decreased infection prevalence in the target mice tissues. Silencing of other genes did not significantly affect tick feeding nor the transmission of B. afzelii, suggesting a possible role of these genes rather in Borrelia acquisition or persistence in ticks. Identification of genes and proteins exploited by Borrelia during transmission and establishment in a tick could help the development of novel preventive strategies for Lyme borreliosis.

• Keywords
• Borrelia afzelii, Ixodes ricinus, RNAi, massive analysis of cDNA ends (MACE), midgut, tick, transcriptome,
• MeSH
• Borrelia burgdorferi Group genetics   MeSH
• Ticks genetics   microbiology   MeSH
• Ixodes genetics   MeSH
• Lyme Disease microbiology   transmission   MeSH
• Mice, Inbred C3H MeSH
• Mice MeSH
• Nymph microbiology   MeSH
• Transcriptome genetics   MeSH
• Digestive System microbiology   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Quantitative and microscopic tracking of Borrelia afzelii transmission from infected Ixodes ricinus nymphs has shown a transmission cycle different from that of Borrelia burgdorferi and Ixodes scapularisBorrelia afzelii organisms are abundant in the guts of unfed I. ricinus nymphs, and their numbers continuously decrease during feeding. Borrelia afzelii spirochetes are present in murine skin within 1 day of tick attachment. In contrast, spirochetes were not detectable in salivary glands at any stage of tick feeding. Further experiments demonstrated that tick saliva is not essential for B. afzelii infectivity, the most important requirement for successful host colonization being a change in expression of outer surface proteins that occurs in the tick gut during feeding. Spirochetes in vertebrate mode are then able to survive within the host even in the absence of tick saliva. Taken together, our data suggest that the tick gut is the decisive organ that determines the competence of I. ricinus to vector B. afzelii We discuss possible transmission mechanisms of B. afzelii spirochetes that should be further tested in order to design effective preventive and therapeutic strategies against Lyme disease.

• Keywords
• Borrelia, Borrelia afzelii, Ixodes ricinus, Lyme disease, tick-borne pathogens, transmission,
• MeSH
• Arachnid Vectors microbiology   physiology   MeSH
• Borrelia burgdorferi Group physiology   MeSH
• Ixodes microbiology   physiology   MeSH
• Humans MeSH
• Lyme Disease microbiology   transmission   MeSH
• Mice, Inbred C3H MeSH
• Mice MeSH
• Nymph microbiology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Vector-borne diseases constitute 17% of all infectious diseases in the world; among the blood-feeding arthropods, ticks transmit the highest number of pathogens. Understanding the interactions between the tick vector, the mammalian host and the pathogens circulating between them is the basis for the successful development of vaccines against ticks or the tick-transmitted pathogens as well as for the development of specific treatments against tick-borne infections. A lot of effort has been put into transcriptomic and proteomic analyses; however, the protein-carbohydrate interactions and the overall glycobiology of ticks and tick-borne pathogens has not been given the importance or priority deserved. Novel (bio)analytical techniques and their availability have immensely increased the possibilities in glycobiology research and thus novel information in the glycobiology of ticks and tick-borne pathogens is being generated at a faster pace each year. This review brings a comprehensive summary of the knowledge on both the glycosylated proteins and the glycan-binding proteins of the ticks as well as the tick-transmitted pathogens, with emphasis on the interactions allowing the infection of both the ticks and the hosts by various bacteria and tick-borne encephalitis virus.

• Keywords
• Anaplasma, Borrelia, Carbohydrate-binding, Glycan, Glycobiology, Host, Lectin, Pathogen, TBEV, Tick,
• MeSH
• Anaplasma pathogenicity   MeSH
• Borrelia pathogenicity   MeSH
• Glycomics methods   MeSH
• Glycosylation MeSH
• Host-Pathogen Interactions physiology   MeSH
• Ixodes microbiology   physiology   virology   MeSH
• Lectins metabolism   MeSH
• Tick-Borne Diseases physiopathology   MeSH
• Polysaccharides metabolism   MeSH
• Proteomics MeSH
• Carbohydrates physiology   MeSH
• Encephalitis Viruses, Tick-Borne pathogenicity   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Lectins MeSH
• Polysaccharides MeSH
• Carbohydrates MeSH