Tools to aid the diagnosis of equine allergy.

The research article discusses the development of a tool to aid in the diagnosis and study of equine (horse) allergic diseases, notably those mediated by Immunoglobulin E (IgE) – a type of antibody involved in allergic reactions.

About Allergies and IgE

• Allergies, or Type I hypersensitivity, are caused by pathological immune responses to usually harmless substances known as allergens. These reactions are primarily mediated by Immunoglobulin E (IgE).
• IgE, like other antibodies, consists of antigen binding sites and a constant Fc-part that is not involved in the recognition of antigens.
• Allergic reactions are initiated when an individual is first exposed to an allergen and B-lymphocytes specific for that allergen are stimulated to differentiate into IgE-producing cells.
• The IgE then binds to IgE Fc-receptors on basophils in the circulation and mast cells in various tissues and initiates the release of inflammatory mediators when the allergen is encountered again.
• These mediators induce immediate vascular and smooth muscle reaction and stimulate the recruitment of eosinophils, basophils, neutrophils, and lymphocytes that cause the late phase inflammatory reaction.
• Allergic diseases can be systemic or localised, affecting the skin, respiratory or digestive tract.

Allergic Diseases in Horses

• The understanding of allergic diseases is primarily based on human medicine and rodent models. In horses, certain conditions like anaphylaxis, urticaria, and Culicoides hypersensitivity are recognised as allergic.
• Other conditions like equine heaves are also suspected to have allergic components. However, experimental studies of equine allergic diseases have been hindered due to the lack of reagents specific for equine IgE.
• While the equine IgE gene has been sequenced, there are yet to be readily available reagents to detect equine IgE. The absence of these reagents makes the clinical diagnosis of allergic diseases in horses also challenging.
• Currently, diagnosis is commonly based on clinical signs, skin tests, and elimination of assumed allergens. Though skin tests can provide valuable information, they are laborious and require specialised skills to perform and interpret.

Immunoassays for Equine IgE Detection

• The research paper discusses the development of a chimeric antibody made up of the equine IgE Fc-part and a murine antigen-recognising part with known specificity.
• As this antibody has an equine Fc-part, it should be able to react with equine mast cells and basophils, initiating an allergic reaction upon administration of its antigen.
• The authors demonstrated that this chimeric IgE molecule mediates the release of histamine from equine basophils in vitro and also mediates an immediate hypersensitivity reaction in horses in vivo.
• Therefore, this chimeric equine-murine IgE can be a valuable research tool to study the mechanisms and cells involved in allergic reactions in horses.