Longitudinal evaluation of immunological responses to allergen-specific immunotherapy in horses with IgE associated dermatological disease, a pilot study

Abstract

Background: The long-term effects of allergen specific immunotherapy (ASIT) on concentrations of circulating immunoglobulin E (IgE) and immunoglobulin G (IgG) in horses have not been reported. Objectives: To document changes in clinical severity of horses with atopic dermatitis (AD) and to monitor allergen-specific IgE and IgG concentrations during a two-year course of ASIT. Animals: Nineteen client-owned horses with a conditional diagnosis of AD. Methods and materials: Three ASIT groups were randomly assigned based upon results obtained by either intradermal testing (IDT) for regional allergens (n = 7); enzyme-linked immunosorbent assay (ELISA) for specific IgE (n = 6); or a composite of results from both tests (n = 6). Serum concentrations of IgE and IgG specific for allergens included in ASIT were measured at time zero and at four-month intervals. A visual analog scale (VAS) was used to record severity of clinical signs at times zero, 12 and 24 months. Results: Positive correlations were documented between IgE and both immediate and delayed IDT results (P < 0.00001), and between immediate IDT and IgG results (P = 0.003). Specific IgE in sera decreased significantly (P < 0.05) for allergens that were included in ASIT, whereas IgG increased. Across all horses, the mean VAS score decreased by 1.2 units [95% CI: 1.28, 1.14; (P < 0.0001)] during each 12-month period of ASIT therapy. Improvement in clinical signs was noted in 76.5% of the horses following 12 months of ASIT and in 82% after 24 months on ASIT. Conclusions and clinical importance: In this pilot study, ASIT in horses with AD provided significant clinical benefit associated with a concomitant reduction of allergen-specific IgE and elevation of IgG.