Background Allergy to bites of blood‐sucking insects, including biting midges, can affect both human and veterinary patients. Horses are often suffering from an IgE‐mediated allergic dermatitis caused by bites of midges (Culicoides spp). With the aim to improve allergen immunotherapy (AIT), numerous Culicoides allergens have been produced as recombinant (r‐) proteins. This study aimed to test a comprehensive panel of differently expressed Culicoides r‐allergens on a cohort of IBH‐affected and control horses using an allergen microarray. Methods IgE levels to 27 Culicoides r‐allergens, including 8 previously unpublished allergens, of which 11 were expressed in more than one expression system, were determined in sera from 347 horses. ROC analyses were carried out, cut‐offs selected using a specificity of 95% and seropositivity rates compared between horses affected with insect bite hypersensitivity (IBH) and control horses. The combination of r‐allergens giving the best performing test was determined using logistic regression analysis. Results Seropositivity was significantly higher in IBH horses compared with controls for 25 r‐allergens. Nine Culicoides r‐allergens were major allergens for IBH with seven of them binding IgE in sera from > 70% of the IBH‐affected horses. Combination of these top seven r‐allergens could diagnose > 90% of IBH‐affected horses with a specificity of > 95%. Correlation between differently expressed r‐allergens was usually high (mean = 0.69, range: 0.28‐0.91). Conclusion This microarray will be a powerful tool for the development of component‐resolved, patient‐tailored AIT for IBH and could be useful for the study of allergy to biting midges in humans and other species.

No abstract

Insect bite hypersensitivity (IBH) is an IgE-mediated dermatitis of horses caused by bites of Culicoides insects, not indigenous to Iceland. Horses born in Iceland and exported to Culicoides-rich areas are frequently affected with IBH. The aims of the study were to compare immunization with recombinant allergens using the adjuvant aluminum hydroxide (Alum) alone or combined with monophosphoryl lipid A (MPLA) for development of a preventive immunization against IBH. Twelve healthy Icelandic horses were vaccinated intralymphatically three times with 10 μg each of four recombinant Culicoides nubeculosus allergens in Alum or in Alum/MPLA. Injection with allergens in both Alum and Alum/MPLA resulted in significant increase in specific IgG subclasses and IgA against all r-allergens with no significant differences between the adjuvant groups. The induced antibodies from both groups could block binding of allergen specific IgE from IBH affected horses to a similar extent. No IgE-mediated reactions were induced. Allergen-stimulated PBMC from Alum/MPLA horses but not from Alum only horses produced significantly more IFNγ and IL-10 than PBMC from non-vaccinated control horses. In conclusion, intralymphatic administration of small amounts of pure allergens in Alum/MPLA induces high IgG antibody levels and Th1/Treg immune response and is a promising approach for immunoprophylaxis and immunotherapy against IBH.

This study shows that specific antibody response can be induced in horses not exposed to Culicoides, using oral treatment with transgenic barley expressing an allergen. Further studies will determine whether this approach is a useful alternative for prevention and treatment of equine insect bite hypersensitivity.

No abstract