Longitudinal analysis of allergen‐specific IgE and IgG subclasses as potential predictors of insect bite hypersensitivity following first exposure to Culicoides in Icelandic horses

Background Insect bite hypersensitivity (IBH) is an allergic dermatitis of horses caused by bites of Culicoides spp. IBH does not occur in Iceland because of the absence of Culicoides, but the prevalence is high in horses imported from Iceland to environments where Culicoides are present. Hypothesis/Objective Test, in a longitudinal study before and after Culicoides exposure, whether a primary sensitizing Culicoides allergen can be identified and if an increase of allergen‐specific immunoglobulin (Ig)E or IgG subclasses precedes clinical signs of IBH. Animals Thirty two horses imported from Iceland to Europe; 16 developed IBH and 16 remained healthy. Methods Determination of IgE and IgG subclasses against recombinant (r)‐Culicoides allergens and Culicoides extract in sera taken before first exposure to Culicoides and yearly over a period of 3–4 years. Results Before Culicoides exposure, there were no significant differences in Culicoides‐specific serum IgE levels between horse that developed IBH or remained healthy. Culicoides exposure induced an individual IgE response pattern (to a median of 4.5 r‐allergens) in the IBH but not in the healthy end‐point group. The increase in serum IgE levels to Culicoides r‐allergens was concurrent with the initial onset of clinical signs of IBH. IBH‐affected horses displayed significantly higher allergen‐specific IgG1 and IgG5 levels than healthy controls. Recombinant Culicoides obsoletus 1 (Cul o1) and Cul o3‐specific IgG5 was significantly higher in the IBH compared to the healthy end‐point group, before clinical signs of IBH. Conclusion/Clinical relevance Allergen‐specific serum IgE cannot be used as predictor for IBH, whereas allergen‐specific IgG5 levels may have a predictive value. Résumé Contexte L'hypersensibilité aux piqures de moustiques (IBH) est une dermatite allergique des chevaux causée par des piqures de Culidcoides spp. L’IBH n'existe par en Islande en raison de l'absence de Culicoides mais la prévalence est élevée chez les chevaux importés d'Islande dans les environnements ou Culicoides est présent. Hypothèses/Objectifs Tester, dans une étude longitudinale avant et après exposition à Culicoides, si une sensibilisation primaire à l'allergène de Culicoides peut être identifiée et si une augmentation d'IgE spécifique d'allergène ou de sous‐classe d'IgG précède les signes clinques d’IBH. Sujets Trente deux chevaux importés d'Island en Europe ; 16 avaient une IBH et 16 étaient sains. Méthodes Déterminer les s