In this study we analysed the presence and proportions of IgE specific for Df 6 and Df 11 two purified allergens of <i>Dermatophagoides farinae</i>. The characterisation of serum IgE and cell-bound IgE for 3 <i>D. farinae</i>-sensitive patients were performed by CRIE, RAST and PRIST assays. Furthermore the basophils from these same patients were studied by histamine release assays in the presence of Df 6 and Df 11. All the individual patient’s cell and serum IgE samples displayed the presence of IgE antibodies specific for Df 6 and Df 11 but the relative quantities of the IgE for these two specificities were characteristic of each patient. The ratios (Specific IgE for Df 11): (Specific IgE for Df 6) (ratio 11:6) were similar in the serum and on the cells for an individual patient. As judged by histamine release assays, the basophil sensitivities towards Df 6 and Df 11 were very different from one atopic patient to another. Moreover cell sensitivities reflected the proportion of Df 6- and Df 11-specific IgE antibodies found in the serum and in the cell eluate.
Ammonium sulphate precipitation and DEAE chromatography is an efficient way of purifying Ag 11, the main allergen in Dermatophagoides farinae mites, which has already been characterized by crossed radioimmunoelectrophoresis. At 60% of saturation in ammonium sulphate, a precipitate is formed which, dissolved and dialysed has been named fraction A 60. It is mainly composed of Ag 11. In the fraction DE obtained by DEAE chromatography of the ammonium sulphate fraction A 60, Ag 11 appears homogeneous on crossed-immunoelectrophoresis. Isoelectrofocusing results indicate an average isoelectric point near neutrality in agreement with the non-absorbtion of Ag 11 on the DEAE cellulose at a weak ionic strength (0.01, at pH 7.2). By sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration Ag 11 has a molecular weight of 28,000.
Ag 11 appears as a single polypeptidic chain with numerous dithio-bonds implying a highly folded and resistant structure. Oligosaccharides could be present as constituting molecules as well as contaminating ones as was assumed for hexosamines. These results are discussed with reference to a similar study performed on the major allergen of Dermatophagoides pteronyssinus. The allergenic properties of Ag 11 as present in fraction DE were tested by RAST-based methods. Fraction DE is an inhibitor as good as Df 80d and when it is coated on paper discs it can bind specific IgE in sera from the majority of mite sensitive patients. The results suggest that Ag 11 is a major allergen from D. farinae.
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