Co-reactivity between related and unrelated environmental allergens in equine allergen-specific IgE serology testing in the UK.

BACKGROUND:Identification of environmental allergens in horses with allergic disease facilitates allergen avoidance and targeted immunotherapy. HYPOTHESIS/OBJECTIVES:To evaluate allergenic co-reactivity between 44 environmental allergens. ANIMALS:Horses with suspected allergic disease (n = 344) whose sera were submitted for environmental allergen testing. METHODS AND MATERIALS:Allergen-specific IgE serological assays were performed using 44 allergens divided into six taxonomically related groups: house dust/storage mites, moulds, insects, grass, tree and weed pollens. Using pairwise comparisons, odds ratios (ORs) were calculated for each environmental pair to determine if there was increased or decreased likelihood of a positive result for one allergen, given a positive result to another. The OR significance was set (using Holm-Bonferroni correction) at P < 0.00006 for all horses (n = 344) and P < 0.00005 for horses with at least one positive reaction (n = 239). Using one-way ANOVA with Tukey's post hoc tests (significance at P < 0.05), differences in mean log e ORs between three groups, taxonomically related allergens with a statistically significant association (related-associated), related allergens lacking a significant association (related-nonassociated) and unrelated allergens were tested. RESULTS:Statistically significant associations were found between both related and unrelated allergen pairs, the former being more frequent. For all horses (n = 344) and horses with at least one positive reaction (n = 239), co-reactivity ranged from 100% (grasses) to 0% (moulds). The weeds group was exceptional in having more co-reactions with another group (grasses). CONCLUSIONS AND CLINICAL IMPORTANCE:Co-reactivity was shown within and between certain related allergen groups. Further studies are required to determine whether this is the result of antigenic cross-reactivity.