Characterization of the main IgE-binding components of cat dander

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 pH 3.9. 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.