Using Western blotting and RAST, this study examined IgE reactivities to Dermatophagoides farinae (Df) extract in three groups of children with either asthma, atopic dermatitis (AD) or a combination of both. The Df antigen presented at least nine distinct IgE-binding bands, with apparent molecular weights of 15, 25, 30, 40, 48, 59, 67, 80 and 110 kD. Positive IgE binding reactions to 15-kD proteins were found in more than 85 of subjects in all three groups, and positive reactions to 25-, 30- and 110-kD proteins in 35–45 in each group. The frequencies of positive IgE binding reaction to other components were generally low in all three groups. The pattern of IgE reactivity to Df components did not differ significantly between the three groups of subjects. IgE-binding activities to two major allergens, Der f1 and Der f2, were also examined by RAST, using recombinant antigens. High RAST reactivities to Der f1 and Der f2 were found in three groups, and the average RAST levels for Der f1 and Der f2 did not differ significantly between the three groups. These findings suggest that a difference in IgE responsiveness to house dust mite antigen is not a major discriminative factor in determining the difference between asthma and A
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