Characterization of an 84 kDa protein inducing an immediate hypersensitivity reaction in rabbits sensitized to Haemaphysalis longicornis ticks

AC-DC electropenetrography unmasks fine temporal details of feeding behaviors for two tick species on unsedated hosts

Ticks are significant nuisance pests and vectors of pathogens for humans, companion animals, and livestock. Limited information on tick feeding behaviors hampers development and rigorous evaluation of tick and tick-borne pathogen control measures. To address this obstacle, the present study examined the utility of AC–DC electropenetrography (EPG) to monitor feeding behaviors of adult Dermacentor variabilis and Amblyomma americanum in real-time. EPG recording was performed during early stages of slow-phase tick feeding using an awake calf host. Both tick species exhibited discernable and stereotypical waveforms of low-, medium-, and high-frequencies. Similar waveform families and types were observed for both tick species; however, species-specific waveform structural differences were also observed. Tick waveforms were hierarchically categorized into three families containing seven types. Some waveform types were conserved by both species (e.g., Types 1b, 1c, 2b, 2c) while others were variably performed among species and individually recorded ticks (e.g., Types 1a, 2a, 2d). This study provides a proof-of-principle demonstration of the feasibility for using EPG to monitor, evaluate, and compare tick feeding behaviors, providing a foundation for future studies aimed at correlating specific feeding behaviors with waveforms, and ultimately the influence of control measures and pathogens on tick feeding behaviors.

Ixodes scapularis saliva components that elicit responses associated with acquired tick-resistance

Ticks and tick-borne diseases are on the rise world-wide and vaccines to prevent transmission of tick-borne diseases is an urgent public health need. Tick transmission of pathogens to the mammalian host occurs during tick feeding. Therefore, it is reasoned that vaccine targeting of tick proteins essential for feeding would thwart tick feeding and consequently prevent pathogen transmission. The phenomenon of acquired tick-immunity, wherein, repeated tick infestations of non-natural hosts results in the development of host immune responses detrimental to tick feeding has served as a robust paradigm in the pursuit of tick salivary antigens that may be vaccine targeted. While several salivary antigens have been identified, immunity elicited against these antigens have only provided modest tick rejection. This has raised the possibility that acquired tick-immunity is directed against tick components other than tick salivary antigens. Using Ixodes scapularis, the blacklegged tick, that vectors several human pathogens, we demonstrate that immunity directed against tick salivary glycoproteins is indeed sufficient to recapitulate the phenomenon of tick-resistance. These observations emphasize the utility of tick salivary glycoproteins as viable vaccine targets to thwart tick feeding and direct our search for anti-tick vaccine candidates.

Whole antigenic lysates of Ixodes ricinus, but not Der-p2 allergen-like protein, are potent inducers of basophil activation in previously tick-exposed human hosts

The clinical suspicion of tick anaphylaxis is based on a history of the bite and occurs often during the warm season. Further arguments are the presence of natural hosts in the immediate environment and, eventually, the identification of the tick. The diagnosis is confirmed when immediate-type sensitization is shown by positive skin prick tests performed with specific tick extracts or the demonstration of specific IgE in vitro. In the current study, we hypothesize that hard tick-derived material contains potent inducers being able to promote basophil stimulation, which correlates with a sensitization immunological response following tick bites. To this end, biological material from two hard tick cell lines (IRE11 and IDE8 - derived from Ixodes ricinus and I. scapularis, respectively) as well as I. ricinus salivary gland and body lysates were used in a human basophil activation test (BAT) to analyse binding and cross-linking capacity of membrane-bound IgE, because basophils are one of the main effector cells of allergic reactions. Additionally, Der-p2 allergen-like gene from I. ricinus was recombinantly expressed as a 15-kDa histidine-tagged fusion protein, purified and included as a stimulus within the setup. Blood was drawn and submitted to BAT screening from a pool of 36 individuals, both bitten and who served solely as negative controls. We have found that seven subjects (19%), all of whom were at least two times tick-bitten, positively reacted to the aforementioned stimuli, whereas the reactivity level of the ones bearing single bites proved to be within the normal range. Moreover, no significant upregulation of the assessed basophil activation marker was detected in the case of Der-p2, except a faint reaction at high dosages. We conclude that at least two tick bites of the human host must occur in order to induce significant basophil activation.

Molecular characterization of Rhipicephalus (Boophilus) microplus Bm86 homologue from Haemaphysalis longicornis ticks

One sequence in the EST database of a midgut cDNA library prepared from semi-engorged female Haemaphysalis longicornis ticks has been found to be a homologue of the Bm86 gene of Rhipicephalus (Boophilus) microplus ticks. The full-length sequence containing a 1785 bp open reading fragment (ORF) was obtained and designated as the Hl86 gene. The predicted amino acid sequence of the Hl86 gene shows a 37% identity to the Bm86 gene. Hl86 is predicted to be a GPI-anchored membrane-bound glycoprotein with a 19-amino acid signal sequence and a 22-amino acid hydrophobic region adjacent to the carboxyl terminus. The most important feature that Hl86 has in common with Bm86 is the repeated pattern of 6 cysteine residues forming epidermal growth factor (EGF)-like domains. RT-PCR analysis showed that Hl86 mRNA transcripts are expressed in all the life cycles of H. longicornis, and the expression was found in the midgut of the adult tick. The Hl86 was expressed in Escherichia coli as a gene10 fusion protein. Mouse anti-recombinant Hl86 serum recognized an 86 kDa protein band in the midgut lysate of semi-engorged ticks in Western blot analysis and showed a strong reaction on the luminal surface of midgut cells in an indirect immunofluorescent antibody test (IFAT). Silencing of the Hl86 gene by RNAi led to a significant reduction in the engorged tick body weight. This is the first report of cloning and characterization of the Bm86 homologue in different genera and species of ixodid and argasid ticks since Bm86 was first reported in 1989.

Anti-tick vaccines

There is now abundant evidence that vaccination with defined protein antigens is able to induce significant immunity to tick infestation. In a limited number of cases, this immunity has been duplicated by vaccination with recombinant antigens, a critical step on the pathway to commercial vaccine production. The existence of two commercial vaccines has allowed a number of field studies showing that the existing products can make an important contribution to an integrated approach to the control of ticks in the field. Under most circumstances however, the use of a tick vaccine as the single, stand alone control technology is likely to require more efficacious vaccines than those currently available. Increases in efficacy are most likely to come through the discovery of additional, effective vaccine antigens. The number of antigens with demonstrated effect is increasing, though only slowly, while the number of potential antigens that remain to be evaluated is increasing more quickly. There is limited, though convincing, evidence that some of these antigens will show effective cross-species protection, though in a poorly understood and unpredictable way. The groundwork has been laid; the potential of the field is still to be effectively exploited.

A cross-reactive tick cement antigen is a candidate broad-spectrum tick vaccine

Truncated constructs of 64P (64TRPs), a secreted cement protein from salivary glands of the tick Rhipicephalus appendiculatus, provided cross-protection against Rhipicephalus sanguineus and Ixodes ricinus, apparently by targeting antigens in the midgut and salivary glands of adults and nymphs, causing mortality. Tick feeding on 64TRP-immunised animals stimulated local inflammatory immune responses (involving basophils, eosinophils, lymphocytes, mast cells, macrophages and dendritic-like cells) that boosted the immune status of vaccinated animals. The vaccine trial results, and antigenic cross-reactivity of 64TRPs with R. sanguineus, I. ricinus, Amblyomma variegatum and Boophilus microplus, indicate the potential of 64TRPs as a broad-spectrum anti-tick vaccine.

Reduced Incidence ofBabesia bigeminaInfection in Cattle Immunized against the Cattle Tick,Boophilus microplus

Boophilus microplus is an important vector of bovine disease agents having a major economic impact on cattle production in many tropical and subtropical countries. Components of tick saliva that enable ticks to feed may also facilitate establishment of tick-borne pathogens in the vertebrate host. It has been suggested that acquired resistance against molecules in tick saliva could inhibit parasite transmission, and there is increasing evidence to support this hypothesis. The effect of immune resistance to B. microplus on the incidence of tick-transmitted pathogens was the focus of this experiment. Groups of four dairy cows were injected with antigen extracts of tick salivary glands, midgut, adjuvant only, or PBS, prior to a grazing period in a pasture in Thailand where ticks are abundant and babesiosis is enzootic. These animals were then observed for evidence of babesiosis throughout the rainy season. A reduction in the incidence of clinical babesiosis was observed among cattle immunized with salivary gland preparations compared to nonimmunized controls (P < 0.05). Immunization with midgut or adjuvant only both resulted in a slight reduction in observed disease compared to the same negative control group. B. bigemina was detected in fewer ticks (24.43%) collected from salivary gland-immunized cattle than those collected from the remaining groups (> or =44.57%). These results indicated that immunization with salivary gland antigens could affect pathogen transmission and appears promising for control of tick-borne diseases of cattle.

Human serum opsonization of orthopedic biomaterial particles: protein-binding and monocyte/macrophage activation in vitro

Wear particles generated after total joint arthroplasty activate monocyte/macrophages and incite formation of a granulomatous periprosthetic tissue associated with bone loss and implant loosening. This study tested the hypothesis that selective opsonization of orthopedic implant biomaterial wear particles by human serum proteins influences monocyte/macrophage activation. Serum protein binding to metallic, polymeric, and ceramic particles was determined by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Individual proteins bound to particles were subsequently identified using two-dimensional SDS-PAGE, microsequencing techniques, and SWISS-PROT analysis. Effects of selective protein opsonization on particle-induced monocyte/macrophage activation were assessed by quantification of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha release. Results from one-dimensional gel analyses revealed distinct serum protein-binding patterns specific for each material tested. Two-dimensional gel analysis together with amino acid sequencing of the prominent protein species confirmed the presence of albumin and alpha-1-antitrypsin bound to all particles tested. In contrast to the metallic particles, apolipoprotein was a major species associated with polymeric particles. Opsonization of PMMA particles with purified preparations of each of the identified proteins showed that albumin significantly enhanced particle-induced monocyte/macrophage activation. These data confirm orthopedic biomaterial specific binding of human serum proteins and demonstrate that albumin exacerbates particle-induced monocyte/macrophage activation. Alterations in the chemical and surface properties of orthopedic biomaterials to modulate protein interactions may improve implant longevity.

Issues in tick vaccine development: identification and characterization of potential candidate vaccine antigens

It is well established that acquired immunity against tick infestation can be induced by repeated tick infestation or by active immunization with either crude or purified native as well as recombinant antigens. This review provides insights into the development of tick vaccines with reference to identification, purification and molecular cloning of candidate target antigens.