A comparison of intradermal testing and detection of allergen-specific immunoglobulin E in serum by enzyme-linked immunosorbent assay in horses affected with skin hypersensitivity

Skin hypersensitivities (allergies) in horses are often diagnosed using clinical signs only. Intradermal testing or serological assays are diagnostic options to confirm the allergic nature of the disease and to identify the allergen(s). Our objective was to develop an allergen-specific enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody specific for horse IgE and to examine its potential for allergen detection in serum in comparison to intradermal testing. Intradermal testing with 61 allergen extracts was performed on 10 horses affected with skin hypersensitivity. Their sera were analyzed by ELISA for IgE antibodies to the same allergens. The kappa test of concordance was used for comparison of the results of both tests. Out of 61 allergen extracts, only two (Timothy and Quack) had kappa values greater than 0.60, suggesting a substantial agreement between skin testing and IgE ELISA. The statistical comparison of the remaining 59 allergens showed little or no concordance between the tests beyond chance. To identify parameters that may influence the sensitivity of the ELISA, the assay was modified to detect allergen-specific IgGb and IgG(T) in serum, and the protein content in all allergen extracts was determined by SDS-PAGE. The commercial allergen extracts revealed a high variation in detectable protein. High concentrations of allergen-specific IgG in horse serum were found to compete with IgE for binding to the plates. In conclusion, an ELISA using whole serum and crude allergen preparations provides limited diagnostic information in horses. The reliable diagnosis of allergens in equine skin hypersensitivity is essential to improve allergen-specific treatments, such as hyposensitization, or the development of allergy vaccines.