Amblyomma americanum: sequential histological analysis of larval and nymphal feeding sites on guinea pigs

Chemical Equilibrium at the Tick-Host Feeding Interface:A Critical Examination of Biological Relevance in Hematophagous Behavior

Ticks secrete hundreds to thousands of proteins into the feeding site, that presumably all play important functions in the modulation of host defense mechanisms. The current review considers the assumption that tick proteins have functional relevance during feeding. The feeding site may be described as a closed system and could be treated as an ideal equilibrium system, thereby allowing modeling of tick-host interactions in an equilibrium state. In this equilibrium state, the concentration of host and tick proteins and their affinities will determine functional relevance at the tick-host interface. Using this approach, many characterized tick proteins may have functional relevant concentrations and affinities at the feeding site. Conversely, the feeding site is not an ideal closed system, but is dynamic and changing, leading to possible overestimation of tick protein concentration at the feeding site and consequently an overestimation of functional relevance. Ticks have evolved different possible strategies to deal with this dynamic environment and overcome the barrier that equilibrium kinetics poses to tick feeding. Even so, cognisance of the limitations that equilibrium binding place on deductions of functional relevance should serve as an important incentive to determine both the concentration and affinity of tick proteins proposed to be functional at the feeding site.

Investigation into the α-Gal Syndrome: Characteristics of 261 Children and Adults Reporting Red Meat Allergy

BACKGROUND

Red meat allergy has historically been understood as a rare disease of atopic children, but the discovery of the "α-Gal syndrome," which relates to IgE to the oligosaccharide galactose-α-1,3-galactose (α-Gal), has challenged that notion.

OBJECTIVE

To describe the clinical and immunologic characteristics of a large group of subjects with self-reported allergy to mammalian meat.

METHODS

This was an observational study of 261 children and adults (range, 5-82 years) who presented for evaluation for allergic reactions to mammalian meat. Results were based on serum assays and a detailed questionnaire.

RESULTS

α-Gal specific IgE ≥ 0.35 IU/mL was detected in 245 subjects and symptom onset occurred ≥2 hours after eating mammalian meat in 211 (81%). Component testing supported a diagnosis of α-Gal syndrome in 95%, pork-cat syndrome in 1.9%, and primary beef allergy in 1.1%. Urticaria was reported by 93%, anaphylaxis by 60%, and gastrointestinal symptoms by 64%. Levels of IgE and IgG specific to α-Gal were similar in subjects who reported early- or delayed-onset symptoms, and in those with and without anaphylaxis. Levels of α-Gal specific IgE and severity of reactions were similar among those with and without traditional atopy, and among children (n = 35) and adults (n = 226). Blood group B trended toward being under-represented among α-Gal-sensitized subjects; however, α-Gal specific IgE titers were high in symptomatic cases with B-antigen.

CONCLUSIONS

The α-Gal syndrome is a regionally common form of food allergy that has a characteristic but not universal delay in symptom onset, includes gastrointestinal symptoms, can develop at any time in life, and is equally common in otherwise nonatopic individuals.

The role of saliva in tick feeding

When attempting to feed on their hosts, ticks face the problem of host hemostasis (the vertebrate mechanisms that prevent blood loss), inflammation (that can produce itching or pain and thus initiate defensive behavior on their hosts) and adaptive immunity (by way of both cellular and humoral responses). Against these barriers, ticks evolved a complex and sophisticated pharmacological armamentarium, consisting of bioactive lipids and proteins, to assist blood feeding. Recent progress in transcriptome research has uncovered that hard ticks have hundreds of different proteins expressed in their salivary glands, the majority of which have no known function, and include many novel protein families (e.g., their primary structure is unique to ticks). This review will address the vertebrate mechanisms of these barriers as a guide to identify the possible targets of these large numbers of known salivary proteins with unknown function. We additionally provide a supplemental Table that catalogues over 3,500 putative salivary proteins from various tick species, which might assist the scientific community in the process of functional identification of these unique proteins. This supplemental file is accessble fromhttp://exon.niaid.nih.gov/transcriptome/tick_review/Sup-Table-1.xls.gz.

Immunological control of hematophagous arthropod vectors: utilization of novel antigens

Immunological control of ixodid ticks requires development of a vaccine that stimulates an effective anti-tick response. However, it is important to avoid induction of intense host skin reactivity to tick feeding. Salivary-gland-derived molecules are introduced into the host during ixodid engorgement; therefore, use of these moieties might not be an optimal immunization strategy. Antigens not normally involved in acquired resistance can be used to induce anti-tick immunity. These "novel" antigens, obtained from tick gut absorptive surface, are not introduced into the host during tick feeding, but are exposed to host-immune effector elements in the blood meal, resulting in ixodid rejection, prevention of ova production and death. Anti-tick immunity is induced with microgram quantities of this ixodid gut antigen preparation. Sera obtained from immunized animals were used to identify antibody-reactive components of the resistance-inducing extract. Tick gut absorptive surface antigen glycoconjugates were identified by lectin blotting, using a series of probes with different carbohydrate specificities. The lectins, peanut and wheat germ agglutinin, and immunized host antibodies bound extract components with similar molecular weights. Solubilization and fractionization of tick gut proteins with the non-ionic detergent Triton X-114 is described.

Ixodid-host immune interaction. Identification and characterization of relevant antigens and tick-induced host immunosuppression

Ixodid ticks are the most important vectors of pathogens to domestic and wild animals. It is established that cattle and laboratory animal species acquire resistance to tick infestation; acquired resistance has an immunological basis consisting of cell-mediated, antibody-mediated and complement-dependent effector mechanisms. Even though acquired resistance to tick feeding is expressed, host immune competence is possibly impaired during the course of tick feeding. Ixodid-induced transient immunosuppression could possibly facilitate the transmission of vector-borne pathogens and/or enhance tick feeding capabilities in the presence of a host immune response to the hematophagous arthropod. Tick tissue extracts have been used to artificially induce resistance to ixodid feeding, and this has become an area of increasing interest as a possible strategy for tick control. It is essential to have defined antigenic molecules for analysis of host responses to infestation, characterization of immunopathologic processes and for vaccine development. This report focuses on attempts to identify, characterize and isolate tick immunogens. Protein immunoblotting, utilizing sera from animals of different genetic composition and infestation patterns, was used to detect a number of tick polypeptides which are reactive with sera of infested hosts. It is clear that infestation with one ixodid species stimulates antibodies reactive with molecules derived from the sensitizing species and/or tick species in the same genus or different genera. This approach is used to identify molecules that are good candidates for use in immunization studies and for analysis of mechanisms involved in acquisition and expression of resistance to tick feeding.

Bovine resistance to Amblyomma americanum ticks: an acquired immune response characterized by cutaneous basophil infiltrates

Purebred Holstein calves acquired resistance to Amblyomma americanum adult ticks after 1 infestation and expressed resistance during a challenge infestation 26 days later. Tick yields from resistant animals were normal, but mean tick weight and egg-mass weight were reduced significantly (31 and 32%, respectively). Cutaneous cellular responses at tick feeding sites in primary (naive) hosts consisted almost exclusively of mononuclear cells, until 24-h post-infestation when granulocytes appeared. At 48 h, basophils were the most abundant granulocyte and comprised 19% of the total cellular response. Secondary and tertiary hosts expressed significant cutaneous basophil responses as early as 6 h post-tick infestation, indicative of an anamnestic response. Cutaneous basophil levels in tertiary hosts (16-34% of the infiltrate) were increased by 2-fold over secondary hosts (12-16% of the infiltrate). Neutrophils and eosinophils were fairly abundant in secondary hosts (22-33%, and 3-13%, respectively), but decreased significantly in tertiary hosts corresponding to increased basophil levels. Mast cells comprised less than 10% of the cells found in primary hosts, and less than 5% in secondary and tertiary hosts representing a consistent, but insignificant component of the total cells. Basophils were not observed in the blood of hosts during any tick infestation, but a peripheral blood basophilia (0.1-1.1%) marked the end of each tick feeding period. A neutropenia was observed in the blood of tertiary hosts corresponding to a decreased tissue neutrophil response. Blood eosinophil, lymphocyte and monocyte levels remained unchanged during each tick infestation compared to controls. In summary, calves acquired immunity to A. americanum ticks, resulting in significant decreases in feeding and ovipositional success associated with a local cutaneous basophil response and peripheral blood basophilia. These findings suggest that basophils are involved in bovine immunity to ticks as has been established in the guinea pig model.

Immunomodulation of host responses to ectoparasite infestation--an overview

Immune reactivity stimulated by ectoparasites and other arthropods has received increased attention in recent years. It is clear that a broad range of host responses are elicited, and immune effector mechanisms appear to be active in limiting infestation with blood-feeding arthropods. Host immune responsiveness appears to be altered as a consequence of infestation by certain arthropods, and the impact of these alterations on vector-borne pathogen transmission remains to be determined. Successful techniques have been developed by a number of investigators for the artificial induction of resistance to blood-feeding arthropods. These areas are examined in this paper.

Ixodes holocyclus: kinetics of cutaneous basophil responses in naive, and actively and passively sensitized guinea pigs

In guinea pigs, macroscopic cutaneous reactions to initial (primary) Ixodes holocyclus feeding were first apparent at 96 hr post-tick attachment, peaked at 7 days (5 mm), and were gone by Day 14. Microscopic analyses of these primary tick feeding sites at 12, 24, 48, 72, and 96 hr post-attachment revealed the dominance mononuclear cells (63-94% of the infiltrate) at all times. Neutrophil levels were high initially (34% of the infiltrate), but quickly subsided to 6-15% of the cellular response. Eosinophils were essentially absent from primary sites, comprising only 1-3% of the infiltrate. Basophils were absent initially, but accumulated in small but significant numbers (12% of the infiltrate) at the epidermal-dermal border by 96 hr post-tick attachment, 3 days prior to maximum erythematous skin reactions. In sensitized and challenged (secondary) animals, erythematous reactions in response to secondary tick feeding were apparent as early as 18 hr post-tick attachment with peak responses at 48 hr (3-4 mm). Cutaneous leukocyte responses to challenge feedings were quantitated at 12, 24, 48, and 72 hr post-tick attachment and consisted initially (12-24 hr) of a strong mononuclear cell response (72-79% of the infiltrate) that was replaced by a dominant basophil response at 48 and 72 hr. Strong cutaneous basophil responses coincided with a significant level of tick rejection. Eosinophils and neutrophils were virtually absent from these secondary responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of hypersensitized guinea pigs to the feeding of Amblyomma americanum ticks

Guinea pigs acquired resistance to the feeding of immature Amblyomma americanum ticks after a single infestation. The initial larval and nymphal feedings resulted in cumulative mortalities of 27.2 and 28.9%, respectively. The second and third larval infestations yielded cumulative mortalities of 50.5 and 52.4%, compared to 18.9 and 24.4% cumulative mortality from controls. Second and third nymphal feedings resulted in 75.7 and 73.4%, and ticks from controls exhibited 36.6 and 34.7% cumulative mortality. The development of host resistance adversely affected tick feeding and resulted in abnormally coloured ticks and a protracted moulting period with a marked decrease in moulting ability. Histological examination of tick feeding sites on guinea pigs challenged twice revealed greater cavity and lesion sizes in hosts fed upon by nymphs than larvae. The primary cell type within these feeding sites were basophils at 12 h post-attachment, but by 72 h post-attachment eosinophils were dominant. The upper epidermal layer adjacent to both larval and nymphal feeding ticks had accumulations of basophils with a few eosinophils. Lymphocytes may have been involved in the resistance response because local lymph nodes in resistant hosts were much larger than in uninfested and singly infested hosts. Some of these nodes had secondary germinal centres.