Evaluation of a commercially available enzyme-linked immunosorbent assay for the detection of allergen-specific IgE antibodies in dogs

Detection of Serum Allergen-Specific IgE in Atopic Dogs Tested in Northern Italy: Preliminary Study

Canine atopic dermatitis (CAD) is a pruritic allergic skin disease associated with IgE-mediated hypersensitivity. IgE is detected using Serum Allergen-Specific IgE test (SAT) in order to identify allergens. The present study aims to identify the environmental allergens in atopic dogs living in Northern Italy using SAT. The screening SAT (sSAT), using a monoclonal antibody cocktail-based ELISA to identify indoor and outdoor allergens, was performed. In all positive samples, an anti-IgE monoclonal antibody ELISA test was performed to extend panel of allergens. Out of 117 selected dogs, 69 were included in the study; 71% were positive and 29% were negative to sSAT. Among the 49 positive sSAT, 53% were positive for both indoor and outdoor, 38.8% only for indoor, and 8.2% only for outdoor allergens. This is the first study on the frequency of allergens involved in CAD in Italy using SAT. IgE hypersensitivity in atopic dogs of Northern Italy is usually associated with indoor allergens, primarily house dust mites. Among the outdoor allergens, an important role was played by Rumex acetosa. Polysensitization also commonly occurs. Therefore, since the numerous factors affect the IgE positivity in CAD, specific panels for geographical areas should be considered and re-evaluated at time intervals.

A descriptive study of allergen-specific IgE serological tests for canine atopic dermatitis in Thailand

Background

This study describes the usefulness of allergen-specific Immunoglobulin E (IgE) serology (ASIS) for identifying allergens in dogs with atopic dermatitis. ASIS tests were conducted in 23 dogs diagnosed with atopic dermatitis for indoor allergens (yeast and mites), outdoor allergens (grass pollen, weed pollen, and tree pollen), and fleas. The relationship among positive ASIS tests were determined using Pearson’s correlation coefficient (r).

Results

Of the atopic dogs, 26.09%, 4.35%, and 47.83% had positive ASIS tests for only indoor allergens, only outdoor allergens, and both indoor and outdoor allergens, respectively. The prevalence of positive ASIS tests was highest for mites (69.57%) and did not differ between indoor and outdoor allergens by age, breed, or sex. The prevalence of positive ASIS tests for indoor allergens during the rainy season (84.21%) was significantly higher than during winter (25.00%, P-value = 0.030). The correlation coefficient of the ASIS results among the outdoor allergens indicated a strong correlation between grass and tree pollen (r = 0.840, P-value < 0.01), grass and weed pollen (r = 0.812, P-value < 0.01), and tree and weed pollen (r = 0.714, P-value < 0.01). The correlation coefficient of the ASIS results of D. farinae indicated a strong correlation with A. siro (r = 0.951, P-value < 0.01) and a moderate correlation with B. tropicalis (r = 0.656, P-value < 0.01) and T. putrescentie (r = 0.672, P-value < 0.01).

Conclusions

ASIS tests are useful in screening for multiple allergens in dogs with atopic dermatitis. Dust mites are an important source of indoor allergens and may be responsible for a higher titer of IgE antibodies against indoor allergens during the rainy season.

Canine atopic dermatitis: detailed guidelines for diagnosis and allergen identification

BACKGROUND

Canine atopic dermatitis (AD) is a common, genetically predisposed, inflammatory and pruritic skin disease. The variation in clinical presentations, due to genetic factors, extent of the lesions, stage of the disease, secondary infections, as well as resemblance to other non-atopic related skin diseases, can complicate a diagnosis of canine AD. A sub-group of the International Committee for Allergic Diseases in Animals (ICADA) was tasked with the development of a set of practical guidelines that can be used to assist practitioners and researchers in the diagnosis of canine AD. Online citation databases and abstracts from international meetings were searched for publications related to the topic, and combined with expert opinion where necessary. The final set of guidelines was approved by the entire ICADA committee.

RESULTS

A total of 81 publications relevant for this review were identified. The guidelines generated focus on three aspects of the diagnostic approach: 1. Ruling out of other skin conditions with clinical signs resembling, or overlapping with canine AD. 2. Detailed interpretation of the historical and clinical features of patients affected by canine AD. 3. Allergy testing by intradermal versus allergen-specific IgE serum testing.

CONCLUSIONS

The diagnosis of canine AD is based on meeting clinical criteria and ruling out other possible causes with similar clinical signs. Flea combing, skin scraping and cytology should be performed, where necessary, as part of a thorough work-up. Elimination diet trials are required for patients with perennial pruritus and/or concurrent gastrointestinal signs. Once a clinical diagnosis of canine AD is made, allergy testing can be performed to identify potential causative allergens for allergen-specific immunotherapy.

Aptamer-based detection and quantitative analysis of human immunoglobulin E in capillary electrophoresis with chemiluminescence detection

A novel aptamer-based CE with chemiluminescence (CL) assay was developed for highly sensitive detection of human immunoglobulin E (IgE). The IgE aptamer was conjugated with gold nanoparticles (AuNPs) to form AuNPs-aptamer that could specifically recognize the IgE to produce an AuNPs-aptamer-IgE complex. The mixture of the AuNPs-aptamer-IgE complex and the unbounded AuNPs-aptamer could be effectively separated by CE and sensitively detected with luminol-H2 O2 CL system. By taking the advantage of the excellent catalytic behavior of AuNPs on luminol-H2 O2 CL system, the ultrasensitive detection of IgE was achieved. The detection limit of IgE is 7.6 fM (S/N = 3) with a linear range from 0.025 to 250 pM. Successful detection of IgE in human serum samples was demonstrated and the recoveries of 94.9-103.2% were obtained. The excellent assay features of the developed approach are its specificity, sensitivity, adaptability, and very small sample consumption. Our design provides a methodology model for determination of rare proteins in biological samples.

Evaluation of a diagnostic ELISA for insect bite hypersensitivity in horses using recombinant Obsoletus complex allergens

Culicoides spp. of the Obsoletus complex belong to the most important species of midge, involved in causing insect bite hypersensitivity (IBH) in horses in The Netherlands. The aim of the current study was to evaluate seven different Obsoletus complex-derived recombinant allergens (Cul o 1-Cul o 7) and to compare these with Obsoletus complex whole body extract (WBE) in an IgE ELISA, using sera of 194 clinically-confirmed cases of IBH and 175 unaffected horses. The highest test accuracy was obtained with WBE, followed by Cul o 2, 3 and 5. Two ELISAs with a combination of recombinant allergens, Combi-1 (Cul o 3, 5 and 7) and Combi-2 (Cul o 1, 2, 5 and 7) were additionally performed and both resulted in high test accuracies close to that obtained with WBE. Combi-1 resulted in the best sensitivity and specificity, both 89%. Both Combi-1 and Combi-2 performed less well with samples collected in winter, but over 70% of the IBH-affected horses could still be identified. In conclusion, a combination of three Obsoletus complex recombinant allergens (Cul o 3, 5 and 7) could potentially replace Obsoletus complex WBE in an IgE ELISA for diagnosis of IBH in horses.

Detection of Allergen-Specific IgE Antibody Responses

Allergen-specific IgE production is the central event in the pathogenesis of atopic disorders and increases in specific IgE serum antibodies are an indicator of immediate hypersensitivity responses in humans and in animal models of allergy. Consequently, accurate and user-friendly methods are needed to measure serum levels of allergen-specific IgE. This review examines historical and recent developments in in vivo and in vitro methods for the detection of allergen-specific IgE in humans and in animal models. Routinely, in vitro methods such as enzyme-linked immunosorbant assays or radioallergosorbant tests and in vivo methods such as the skin prick test (SPT) for humans and the passive cutaneous anaphylaxis assay (PCA) used in animals are utilized to detect allergen-specific IgE. While in vivo assays are usually more accurate than in vitro assays since they provide a functional readout of IgE activity, they are relatively costly and require considerable expertise. On the other hand in vitro assays are limited by the fact that the amount of allergen-specific serum IgG exceeds IgE antibody by several orders of magnitude, resulting in competition for allergen binding. Consequently, methods that use allergen as a direct capture step are limited by the availability of free allergen binding sites for IgE. In order to circumvent this problem, in vitro methods usually require prior depletion of IgG or use high amounts of allergen in order to facilitate availability of free binding sites for IgE detection. Clearly, these approaches are limited for small sample volumes and allergens that are in short supply. New methods such as protein microarray could potentially overcome this problem by providing high allergen concentrations in a relatively small reaction volume. Currently, in vitro methods are rarely used in isolation for prognosis but are used primarily to complement the information obtained from in vivo assays. With the emergence of new technologies it is conceivable that in vitro assays may in the future replace in vivo assays, however until then in vivo assays remain the gold standard of allergen-specific IgE detection.

Evaluation of an in vitro sulphidoleukotriene release test for diagnosis of insect bite hypersensitivity in horses

REASONS FOR PERFORMING STUDY

Insect bite hypersensitivity (IBH) is an IgE-mediated allergic dermatitis caused by bites of Culicoides and Simulium species, and improved means of diagnosis are required.

OBJECTIVES

The cellular antigen simulation test (CAST) with C. nubeculosus and S. vittatum extracts was assessed in a population of IBH-affected and healthy horses. Variations in test results over a one year period and possible cross-reactivity between different insect extracts was studied.

METHODS

A total of 314 mature horses were studied using the CAST. Influence of severity of clinical signs, gender and age were evaluated, and 32 horses were tested repeatedly over one year. The kappa reliability test was used to assess agreement of the test results with different insect extracts.

RESULTS

Horses with IBH had significantly higher sLT release than controls with C. nubeculosus and S. vittatum. The highest diagnostic sensitivity and specificity levels were attained when using adult C. nubeculosus extracts with the CAST (78% and 97%, respectively), suggesting that most horses with IBH are sensitised against Culicoides allergens. A proportion of IBH-affected horses was found to be sensitised to allergens of Simulium spp. in addition to those of C. nubeculosus. The CAST with C. nubeculosus had positive and negative predictive values > or = 80% for a true prevalence of IBH of 12-52%. In the follow-up study, the proportion of IBH-affected horses with a positive test result ranged from 90% in November to 68% in March. Severity of clinical signs or age did not influence test results significantly. However, IBH-affected males achieved significantly more positive test results than IBH-affected females.

CONCLUSIONS

The CAST with adult C. nubeculosus has high specificity and good sensitivity for diagnosis of IBH. Horses with IBH are mainly sensitised to Culicoides allergens, and some horses are additionally also sensitised to allergens in Simulium spp.

POTENTIAL RELEVANCE

The CAST is likely to be a useful test for diagnosis of IBH, even allowing the identification of IBH-affected but asymptomatic horses. This test may also help in further characterisation of allergens involved in this condition.

Inter-laboratory comparisons of assessment of the allergenic potential of proteins in mice

Assessment of the potential allergenicity of novel proteins, including those expressed in genetically modified plants, is an important issue. In previous studies, we have shown that the IgE measurement induced by systemic exposure of BALB/c mice to a range of proteins correlates broadly with what is known of their allergenic potential in humans. The approach used a homologous passive cutaneous anaphylaxis (PCA) assay that reflects IgE-dependent biological activity and is of sufficient sensitivity to detect IgE production in the absence of adjuvant. In previous studies, the immunization phase was conducted independently in two separate facilities, and the subsequent analytical work (PCA) conducted in a single facility. The purpose here was to further evaluate the transferability of this approach. To this end, BALB/c mice were exposed to a range of doses of peanut agglutinin or ovalbumin, allergenic proteins of peanut and hen's egg, respectively, in two independent laboratories. Serial doubling dilutions of serum pooled for each treatment group were analyzed for specific IgE. At higher doses of allergen very similar, or identical, IgE titers were achieved in both laboratories, although at lower doses, responses were somewhat more variable. These data demonstrate that, although technically demanding, the measurement of protein allergen-induced IgE antibody production in mice using PCA is relatively robust and is transferable and reproducible between laboratories. This approach may provide a useful tool for the safety assessment of novel proteins and suggests that continued evaluation of the approach with a wider range of protein allergens and non-sensitising proteins is justified.

Allergen-specific IgE in Icelandic horses with insect bite hypersensitivity and healthy controls, assessed by FcepsilonR1alpha-based serology

Insect bite hypersensitivity (IBH) and atopy can both be causes of pruritus in horses and are associated with allergen-specific IgE to biting insects and environmental allergens respectively. Information with respect to differences in IgE levels in diseased and healthy animals is crucial in enabling an understanding of the clinical relevance of results of allergen-specific IgE tests. The aim of this study was (i) to evaluate and compare levels of allergen-specific IgE, using an ELISA method, in Icelandic horses, with and without IBH, from Iceland and Sweden respectively; (ii) to investigate patterns of allergen-specific IgE to insects, pollens, moulds and mites in those groups of horses; and (iii) to investigate the clinical significance of employing two different cut-off levels for the ELISA. The study compromised a total number of 99 horses from Iceland and Sweden, with and without IBH, divided in 5 groups. Sera from the horses were analysed blindly with the use of Allercept , a non-competitive, solid-phase ELISA-test, designed to detect the presence of allergen-specific IgE in sera using the recombinant alpha chain of the high-affinity IgE receptor (FcepsilonR1alpha). The distribution of the ELISA values was shown for each insect, mould, mite and pollen allergen, in the different groups using 10th, 50th and 90th percentiles. The use of two cut-off levels, 150 EA and 300 EA, did not eliminate the false positives. Horses with IBH had a higher number of positive reactions, counting all the 29 allergens, than healthy controls and this was borderline significant (P=0.053). In this study it was shown that serological testing with an ELISA that uses the high-affinity IgE receptor (FcepsilonR1alpha) is presently not suitable as a tool for establishing a diagnosis of IBH or equine atopy. The importance of establishing a correct cut-off level for the ELISA for the different allergens is emphasised.

Lymphocyte blastogenic response to ovalbumin in a model for canine allergy

Lymphocyte stimulation tests (LST) were performed in five dogs sensitised with ovalbumin (OVA) and seven healthy dogs. In addition, all five OVA-sensitised and two control dogs were tested after two in vivo provocations with OVA-containing eye drops. The isolated cells were suspended in culture media containing OVA and were cultured for up to 12 days. Proliferation was measured as reduction in 5,6-carboxylfluorescein diacetate succinimidyl ester (CFSE) intensity by flow cytometry on days 0, 3, 6, 9 and 12. A cell proliferation index (CPI) for each day and the area under the curve (AUC) of the CPI was calculated for each dog. All OVA-sensitised dogs demonstrated increased erythema after conjunctival OVA application. The presence of OVA-specific lymphocytes was demonstrated in 2/5 OVA-sensitised dogs before and 4/5 after in vivo provocation. Using the AUC, the difference between OVA-sensitised and control dogs was significant in all three LST before in vivo provocation (P<0.05) and borderline significant (P=0.053) in 2/3 LST after provocation. The most significant difference in CPI was observed after 9 days of culture (P=0.001). This pilot study indicates that the LST allows detection of rare antigen specific memory T-cells in dogs previously sensitised to, but not concurrently undergoing challenge by a specific antigen.

Cheyletiella infestation in the dog: observations on diagnostic methods and clinical signs

The aims of this study were to evaluate the ability of diagnostic methods to detect naturally occurring Cheyletiella infestation in dogs, and to quantify and relate the number of mites and eggs present to clinical signs. Privately owned dogs with skin problems were eligible for inclusion in the study. Four diagnostic tests were performed on each dog in the following order: tape impression, hair plucking, skin scraping and vacuum cleaning. Dogs with positive test results for Cheyletiella infestation in at least one of the tests under evaluation were included in the study (n=27). The severity of pruritus and scaling was graded on a four-point fixed scale. The diagnostic findings in vacuum cleaning samples provided a semiquantitative measure of the grade of infestation. The vacuum cleaning test gave a positive test result in all dogs and was significantly more efficient than the other tests evaluated (P<0.01). The number of diagnostic findings varied considerably among the different vacuum samples. No significant relationship between the number of diagnostic findings and severity of clinical signs was detected.