Identification and anticoagulant activity of a novel Kunitz-type protein HA11 from the salivary gland of the tick Hyalomma asiaticum

Proteases and protease inhibitors in saliva of hard ticks: Biological role and pharmacological potential

Hard ticks (family Ixodidae) are significant vectors of pathogens affecting humans and animals. This review explores the composition of tick saliva, focusing on proteases and protease inhibitors, their biological roles, and their potential in vaccines and therapies. Tick saliva contains various proteases, mostly metalloproteases, serpins, cystatins, and Kunitz-type inhibitors, which modulate host hemostatic, immune, and wound healing responses to facilitate blood feeding and pathogen transmission. Proteases inhibit blood clotting, degrade extracellular matrix components, and modulate immune responses. Serpins, cystatins, and Kunitz-type inhibitors further inhibit key proteases involved in coagulation and inflammation, making them promising candidates for anticoagulant, anti-inflammatory, and immunomodulatory therapies. Several tick proteases and protease inhibitors have shown potential as vaccine targets, reducing tick feeding success and pathogen transmission. Future research should focus on comprehensive proteomic and genomic analyses, detailed structural and functional studies, and vaccine trials. Advanced omics approaches and bioinformatics tools will be crucial in uncovering the complex interactions between ticks, hosts, and pathogens, improving tick control strategies and public health outcomes.

Tick Salivary Kunitz-Type Inhibitors: Targeting Host Hemostasis and Immunity to Mediate Successful Blood Feeding

Kunitz domain-containing proteins are ubiquitous serine protease inhibitors with promising therapeutic potential. They target key proteases involved in major cellular processes such as inflammation or hemostasis through competitive inhibition in a substrate-like manner. Protease inhibitors from the Kunitz superfamily have a low molecular weight (18-24 kDa) and are characterized by the presence of one or more Kunitz motifs consisting of α-helices and antiparallel β-sheets stabilized by three disulfide bonds. Kunitz-type inhibitors are an important fraction of the protease inhibitors found in tick saliva. Their roles in inhibiting and/or suppressing host homeostatic responses continue to be shown to be additive or synergistic with other protease inhibitors such as cystatins or serpins, ultimately mediating successful blood feeding for the tick. In this review, we discuss the biochemical features of tick salivary Kunitz-type protease inhibitors. We focus on their various effects on host hemostasis and immunity at the molecular and cellular level and their potential therapeutic applications. In doing so, we highlight that their pharmacological properties can be exploited for the development of novel therapies and vaccines.

Cloning and functional identification of pmKPI cDNA in Poecilobdella manillensis

BACKGROUND

Kazal-type serine protease inhibitors play a role in physiological processes such as blood coagulation and fibrinolysis. The amino acid residues at the P1 site are different, and they inhibit different types of proteases. The inhibitory mechanism of the protease in the salivary glands of Poecilobdella manillensis is still unclear.

METHODS AND RESULTS

Based on cloning, prokaryotic expression and bioinformatics analysis, we studied the role of Kazal-type serine protease inhibitors in P. manillensis and analyzed their expression by quantitative real-time PCR. The results suggested that the recombinant protein was successfully expressed in the supernatant when a prokaryotic expression vector was constructed and induced with 0.2 mmol/L IPTG at 37 °C for 4 h, and the enzymatic activity was determined. The mature protein encodes 91 amino acids and has a relative molecular weight of 9929.32 Da, and after removing the signal peptide, the theoretical isoelectric point was 8.79. It is an unstable protein without a transmembrane domain. The mature protein contains two Kazal-type domains, in which all P1 residues are Lys, consisting of an α helix and three antiparallel β sheets. The upregulated expression of the mRNA was induced after a meal was provided, and the results showed an increasing and then decreasing trend.

CONCLUSIONS

Taken together, the results indicate that mature proteins from P. manillensis inhibit thrombin activity, laying the foundation for the subsequent in-depth study of the function of genes encoding Kazal-type serine protease inhibitors.

Recombinant cysteine proteinase as anti-tick targeting Hyalomma asiaticum infestation

Cysteine proteases are involved in the digestion of host blood and the degradation of yolk proteins of arthropod ectoparasites. In this study, a cathepsin L-like cysteine proteinase gene (HasCPL) of Hyalomma asiaticum was cloned, and recombinant (r)HasCPL protein was generated for immunization study. Bioinformatic analysis confirmed HasCPL was a member of the papain family (clan CA) and have high sequence identities with CPLs of other Ixodid ticks. The efficacy of immunization against H. asiaticum infestations in rabbits was assessed. Rabbits (n = 3) were immunized three times with rHasCPL before challenged with 250 larvae per rabbit four weeks post-immunization. A high antibody titer was detected in immunized rabbits in comparison to control. Western blot analysis detected CPLs in midgut, salivary gland, and ovary. Increase of rejection percentage of larvae were noted in ticks fed on immunized animals in comparison to control. Overall, a 55.09% protection against larva ticks was noted.

Characterization of a single-domain von Willebrand factor type C protein (HaSVC) from the salivary gland of the tick Hyalomma asiaticum

As a widely distributed arthropod and vector for various pathogens, Hyalomma asiaticum presents great risk and potential losses in animal husbandry. Effective measures, including the use of vaccines, are necessary for controlling ticks and tick-borne diseases. A concise understanding of the tick-host interaction associated molecules and pathways is required for vaccine development. In the present study, a protein containing a single-domain von Willebrand factor type C (HaSVC) was isolated from H. asiaticum and was subjected to functional identification. As a result, the full-length sequence of the HaSVC (506 bp) gene was obtained, which putatively encodes 100 amino acids with a predicted molecular mass of 11 kDa, excluding the 23-amino acid signal peptide. HaSVC contains 8 cysteines to form 4 disulfide bonds. The native HaSVC protein was detected in multiple tick organs. HaSVC neither attenuated the anti-coagulation process nor directly affected the blood feeding of adult ticks. However, the purified recombinant protein HaSVC (rHaSVC/GST) significantly increased the proliferation of mice spleen cells. This might suggest a regulatory function for HaSVC on inflammation, thus providing new information that may explain the "crosstalk" between ticks and hosts.

Transcriptome analysis of the innate immune system of Hyalomma asiaticum

Ticks are considered to be the second most important vectors of human infectious diseases. The innate immune system is the key factor that affects its vector competence. Hyalomma asiaticum is the primary vector of Crimean-Congo hemorrhagic fever virus (CCHFV). However, the immune system of H. asiaticum remains virtually unknown. Here, a high throughput full-length mRNA sequencing method was adopted to define the immunotranscriptome of H. asiaticum infected with the fungal pathogen Beauveria bassiana and gram-negative bacterium Enterobacter cloacae. The analysis yielded 22,300 isoforms with an average length of 3233 bps. In total, 68 potential immunity-related genes were identified based on similarity to the homologs known to be involved in immunity. These included most members of the Toll and JAK/STAT signaling pathways, but not the IMD signaling pathway. Moreover, two copies of Dicer-2 and five copies of Argonaute-2 were detected. These genes are postulated to be involved in the RNA interference (RNAi) pathway, which is an important defense against RNA viruses. Overall, this study provides the foundation for understanding the immune response of H. asiaticum to CCHFV.

Tick-Borne Encephalitis Virus Infection Alters the Sialome of Ixodes ricinus Ticks During the Earliest Stages of Feeding

Ticks are hematophagous arthropods that transmit a number of pathogens while feeding. Among these is tick-borne encephalitis virus (TBEV), a flavivirus transmitted by Ixodes ricinus ticks in the temperate zone of Europe. The infection results in febrile illness progressing to encephalitis and meningitis with a possibility of fatality or long-term neurological sequelae. The composition of tick saliva plays an essential role in the initial virus transmission during tick feeding. Ticks secrete a diverse range of salivary proteins to modulate the host response, such as lipocalins to control the itch and inflammatory response, and both proteases and protease inhibitors to prevent blood coagulation. Here, the effect of viral infection of adult females of Ixodes ricinus was studied with the goal of determining how the virus alters the tick sialome to modulate host tissue response at the site of infection. Uninfected ticks or those infected with TBEV were fed on mice and removed and dissected one- and 3-h post-attachment. RNA from the salivary glands of these ticks, as well as from unfed ticks, was extracted and subjected to next-generation sequencing to determine the expression of key secreted proteins at each timepoint. Genes showing statistically significant up- or down-regulation between infected and control ticks were selected and compared to published literature to ascertain their function. From this, the effect of tick viral infection on the modulation of the tick-host interface was determined. Infected ticks were found to differentially express a number of uncategorized genes, proteases, Kunitz-type serine protease inhibitors, cytotoxins, and lipocalins at different timepoints. These virus-induced changes to the tick sialome may play a significant role in facilitating virus transmission during the early stages of tick feeding.

Identification and characterization of vaccine candidates against Hyalomma anatolicum-Vector of Crimean-Congo haemorrhagic fever virus

Crimean-Congo haemorrhagic fever (CCHF) is a tick borne viral disease reported from different parts of the world. The distribution of the CCHF cases are linked with the distribution of the principal vector, Hyalomma anatolicum in the ecosystem. Presently, vector control is mainly dependent on repeated application of acaricides, results in partial efficacy and generated acaricide resistant tick strains. Amongst the different components of integrated management programme, immunization of hosts is considered as one of the sustainable component. To restrict CCHF virus spreading, use of anti-Hyalomma vaccines appears as a viable solution. Accordingly, present study was under taken to characterize and evaluate vaccine potential of two conserved molecules, ferritin2 (FER2) and tropomyosin (TPM). Silencing of the genes conferred a cumulative reduction (rejection + unable to engorge) of 61.3% in FER2 and 70.2% in TPM respectively. Furthermore, 44.2% and 72.7% reduction in engorgement weight, 63.6% and 94.9% reduction in egg masses in FER2 and TPM silenced ticks in comparison to LUC-control group was recorded. The recombinant protein, rHaFER2 was characterized as 35 kDa protein with pI of 5.84 and possesses iron binding domains. While rHaTPM is a 51kDa protein with pI of 4.94 having calcium binding domains. Immunization of cross-bred calves by rHaFER2 conferred 51.7% and 51.2% protection against larvae and adults of H. anatolicum challenge infestations. While rHaTPM conferred 63.7% and 66.4% protection against larvae and adults infestations, respectively. The results were comparable with the data generated by RNAi and it clearly showed the possibility for the development of anti-hyalomma vaccine to manage CCHF virus and Theileria annulata infection in human and animals.

Peptidase inhibitors in tick physiology

Peptidase inhibitors regulate a wide range of physiological processes involved in the interaction between hematophagous parasites and their hosts, including tissue remodeling, the immune response and blood coagulation. In tick physiology, peptidase inhibitors have a crucial role in adaptation to improve parasitism mechanisms, facilitating blood feeding by interfering with defense-related host peptidases. Recently, a larger number of studies on this topic led to the description of several new tick inhibitors displaying interesting novel features, for example a role in pathogen transmission to the host. A comprehensive review discussing these emerging concepts can therefore shed light on peptidase inhibitor functions, their relevance to tick physiology and their potential applications. Here, we summarize and examine the general characteristics, functional diversity and action of tick peptidase inhibitors with known physiological roles in the tick-host-pathogen interaction.

Gut contents, digestive half-lives and feeding state prediction in the soil predatory mite Pergamasus longicornis (Mesostigmata: Parasitidae)

Mid- and hind-gut lumenal changes are described in the free-living predatory soil mite Pergamasus longicornis (Berlese) from a time series of histological sections scored during and after feeding on fly larval prey. Three distinct types of tangible material are found in the lumen. Bayesian estimation of the change points in the states of the gut lumenal contents over time is made using a time-homogenous first order Markov model. Exponential processes within the gut exhibit 'stiff' dynamics. A lumen is present throughout the midgut from 5 min after the start of feeding as the gut rapidly expands. It peaks at about 21.5 h-1.5 days and persists post-feeding (even when the gut is contracted) up until fasting/starvation commences 10 days post start of feeding. The disappearance of the lumen commences 144 h after the start of feeding. Complete disappearance of the gut lumen may take 5-9 weeks from feeding commencing. Clear watery prey material arrives up to 10 min from the start of feeding, driving gut lumen expansion. Intracellular digestion triggered by maximum gut expansion is indicated. Detectable granular prey material appears in the lumen during the concentrative phase of coxal droplet production and, despite a noticeable collapse around 12 h, lasts in part for 52.5 h. Posterior midgut regions differ slightly from anterior regions in their main prey food dynamics being somewhat faster in processing yet being slightly delayed. Posterior regions are confirmed as Last-In-Last-Out depots, anterior regions confirmed as First-In-First-Out conveyor belt processes. Evidence for differential lability of prey fractions is found. A scheme is presented of granular imbibed prey material being first initially rapidly absorbed ([Formula: see text] = 23 min), and also being quickly partly converted to globular material extra-corporeally/extracellularly ([Formula: see text] = 36 min)-which then rapidly disappears ([Formula: see text] = 1.1 h, from a peak around 4 h). This is then followed by slow intracellular digestion ([Formula: see text] = 6.9 h) of the resultant resistant prey residue matching the slow rate of appearance of opaque pre-excretory egestive refractive grains (overall [Formula: see text] = 4.5 days). The latter confirmed latent 'catabolic fraction' (along with Malpighian tubule produced guanine crystals) drives rectal vesicle expansion as 'faeces' during the later phases of gut emptying/contraction. Catabolic half-lives are of the order of 6.3-7.8 h. Membraneous material is only present in the lumen of the gut in starving mites. No obvious peritrophic membrane was observed. The total feeding cycle time may be slightly over 52.5 h. Full clearance in the gut system of a single meal including egestive and excretory products may take up to 3 weeks. Independent corroborative photographs are included and with posterior predictive densities confirm the physiological sequence of ingestion/digestion, egestion, excretion, defecation, together with their timings. Visually dark midguts almost certainly indicate egestive refractive grains (xanthine?) production. Nomograms to diagnose the feeding state of P. longicornis in field samples are presented and show that the timing of these four phases in the wild could be inferred by scoring 10-12 mites out of a sample of 20. Suggestions to critically confirm or refute the conclusions are included.