Monoclonal anti-equine IgE antibodies with specificity for different epitopes on the immunoglobulin heavy chain of native IgE.

In this study we describe the generation of monoclonal antibodies (mAbs), which recognize different epitopes of the equine IgE constant heavy chain. Equi-murine recombinant IgE (rIgE), composed of the murine V(H)186.2 heavy chain variable region, linked to the equine IgE constant heavy chain and expressed together with the murine lambda(1) chain in J558L cells was used to immunize BALB/C mice. A total of 17 different mAbs were obtained, which recognized the rIgE heavy chain constant region. None of the mAbs reacted with monoclonal equine isotypes IgM, IgG1 (IgGa), IgG3 (IgG(T)), IgG4 (IgGb) or isolated equine light chains, IgGc and IgA from horse serum, or the native mAb B1-8delta, expressing the same heavy chain variable regions and light chains. One of the mAbs (alphaIgE-132) recognized the recombinant equine IgE, but did not recognize any protein in equine serum, i.e. native IgE. A total of 16 mAbs detected a serum protein of approximately 210,000Da on Western blots, corresponding to the expected MW of native IgE. In addition, one of the mAbs (alphaIgE-176) detected a protein of 76,000Da under reducing conditions, most likely the equine IgE heavy chain. According to binding inhibition studies, the equine IgE specific mAbs recognize at least two different epitopes of the equine IgE. In an ELISA using two anti-IgE mAbs which recognized different epitopes, no significant differences in the concentration of total serum IgE could be detected between adult Icelandic horses with IgE-mediated type I allergy (summer eczema) and healthy control animals. In Icelandic horse foals, no serum IgE could be measured 6 months post partum. All anti-IgE mAbs recognized a small population (1.3+/-0.5%) of leukocytes from adult Icelandic horses by surface immunofluorescence, but no cells could be detected in foal blood. The stained leukocytes from adult horses could be enriched by magnetic cell sorting and contained 32% basophils, 53% monocytes and/or large lymphocytes, 13% small lymphocytes and 2% eosinophils.