D1.512 - Culicoides allergen induced in vitro sulphidoleukotriene release correlates with clinical lesion severity in Icelandic horses affected with insect bite hypersensitivity

Insect bite hypersensitivity (IBH) is an IgE mediated hypersensitivity reaction to Culicoides salivary allergens. All breeds of horses can get affected but horses in Iceland are not affected as the causative species are not endemic there. However, 25-60% of exported Icelandic horses do suffer from IBH. The allergy is characterized as severe itching, loss of hair and thickening of the skin. Clinical severity varies considerably among affected horses, and reliable, objective biomarkers reflecting disease severity are limited.

Objective: Investigate the association between Culicoides allergen-induced sulphidoleukotriene (sLT) release using major allergens and lesion severity in horses with IBH. Additionally, potential effects of country of birth (Iceland versus continental Europe), sex, and age on sLT release and clinical severity were evaluated. 

Sixty-one Icelandic horses diagnosed with IBH were examined monthly using a standardized lesion scoring system. Peripheral venous blood samples were collected, stimulated with Culicoides obsoletus whole body (WBE) extract and recombinant Cul o 3, Cul o 8, Cul o 9 and Cul o 10b. sLT release was quantified using the Cellular Antigen Stimulation Test (CAST). Associations between sLT release, lesion severity, and age were analyzed using Spearman´s correlation coefficient. The Mann-Whitney U test was applied to evaluate effects of country of birth and sex on maximum lesion score and sLT release.  

Maximum lesion scores correlated significantly with sLT release for all tested allergens (r=0.48-0.60, p<0.001). No correlation with age was found. Horses born in Iceland (n=47) exhibited higher maximum lesion scores (mean 23 versus 13.5, p<0.05) and significantly increased sLT release following stimulation with recombinant allergens (Cul o 3, Cul o 8, Cul o 9, and Cul o 10b) compared to horses born in continental Europe (n=14). No significant group difference was detected after stimulation with C. obsoletus WBE. 

These findings highlight the potential of CAST as an objective biomarker for assessing disease severity in IBH-affected horses. Furthermore, it could serve as a valuable tool for evaluating the efficacy of allergen immunotherapy and other IBH treatments.