Characterization of the Main IgE-Binding Components of Cat Dander

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Abstract
Cat dander extract (CDE) was fractionated by preparative isoelectric focusing (pIEF). All the fractions showed allergenic activity, but the most acidic ones (pH range 3.3–4.3) had the highest specific activity. These fractions also had the highest cat allergen 1 content and a partial antigenic identity as determined by fused rocket immunoelectrophoresis. Immunoblotting of the pIEF fractions and the crude CDE after analytical IEF showed the presence of native proteins with IgE-binding ability all along the pH range 3.3–6.2. However, when the IgE-immunoprecipitated components of the most acidic pIEF fractions were focused in the presence of urea, a neat band was found at pH3.9. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting of CDE proved the presence of, at least, 9 polypeptides with affinity to IgE, those with molecular weights of 18,000 and 22,000 daltons being the most active ones. These polypeptides presumably belong to cat allergen 1 since they were found in the most acidic pIEF fractions as well as in the crossed immunoelectrophoresis arc corresponding to this allergen. Furthermore, we found a group of active proteins with molecular weights of 10,000, 22,000, 25,000, 50,000 and 65,000 daltons (cat albumin) and with isoelectric points between 3.3 and 6.2.