Published online: April 4, 2018
Allergic skin reactions caused by insect bites are the most common type of allergies in horses. One important form of such a skin allergy is called sweet itch, summer eczema or insect-bite hypersensitivity (IBH), and manifests in weeping and bleeding lesions including crust formation, scales, swelling and lichenification of the skin.
Thirty-four sweet itch affected Icelandic horses participated in a placebo-controlled double blinded clinical study performed by Fettelschoss-Gabriel et al., whereof 19 horses received vaccine and 15 horses received placebo. The vaccine consisted of two components coupled together. The first component is a general immune activation part based on a virus-like particle (VLP), and a self-molecule interleukin-5 (IL-5), the master-regulator of eosinophils, a major effector cell type in allergy. Immunization with this conjugate vaccine resulted in IL-5 specific auto-antibodies which neutralize its target thus limiting the number of eosinophils localized to the skin and thereby reducing tissue damage. Lesion scores of horses had been evaluated in the season before and after vaccination.
In a classical type-I allergy the eosinophil is a cell type important during late phase type-I reactions. Fettelschoss-Gabriel et al. have also shown a critical disease-involvement of eosinophils in delayed-type hypersensitivity type-IV reactions (type IVb). This cell type is commonly associated with helminth infections and plays a key role in allergic human asthma; allergic asthma has therefore been suggested to be the human analogue to the horse skin allergy. Indeed, upon vaccination, horses developed antibodies against the eosinophilic master-regulator IL-5, and in turn showed reduced lesion scores in the treatment season when compared to the untreated previous season and also when compared to placebo horses in the same season.
The vaccine was well tolerated and no increase in helminth burden was observed upon vaccination. In contrast to placebo treated horses, vaccinated horses showed strongly reduced skin lesion scores.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.