Development of an in vitro model system for studying the interaction of Equus caballus IgE with its high-affinity receptor FcɛRI

The binding of immunoglobulin E (IgE) to its high-affinity receptor (FcɛRI) is the central protein interaction in IgE-mediated allergic reactions. The cross-linking of the IgE/FcɛRI complex, through cognate allergens, on the surface of mast cells and basophil cells results in mediator release, and thus leads to the symptoms of type I hypersensitivity responses in mammals. To develop a baseline value for subsequent equine anti-allergy drug and vaccine research, the interaction of equine IgE with its high-affinity FcɛRI receptor was investigated following the cloning and expression of equine IgE with specificity for NIP-HSA (4-hydroxy-5-iodo-3-nitrophenylacetic acid conjugated to human serum albumin). Receptor recognition and effector functions were assessed in Rat Basophil Leukemia (RBL-2H3.1) cells transfected with the α chain of equine and canine FcɛRI. Results obtained showed that the equine FcɛRI receptor recognizes both equine and canine IgE and supports similar β-hexosaminidase release levels from RBL cells transfected with equine FcɛRI, peaking at 36.68% at 100 ng ml−1 antigen and 32.00% at 100 ng ml−1 antigen respectively. Furthermore, the binding kinetics of the equine IgE to the equine FcɛRI receptor and the canine IgE to the same receptor was measured to be KA = 6.33 × 109 M−1 and KA = 1.84 × 109 M−1 respectively. This research established basic reagents and vitro assay systems to underpin the development of rational therapeutic intervention strategies to combat equine allergic manifestations.