IgE Responsiveness to Dermatophagoides farinae in Young Asthmatic Children: IgE Binding Study Using Recombinant Allergens of Der f 1, Der f 2 and Mutant Proteins of Der f 2

IgE reactivities to two recombinant (r) allergens, rDer f 1 and rDer f 2, synthetized by cDNA clones from Dermatophagoides farinae (Df) were analyzed using sera of Df-sensitive asthmatic patients of varying ages. Positive RAST responses to rDer f 1 and rDer f 2 were found in 88 and 80%, respectively, with sera from young asthmatic children aged 0-1, positive RAST rates to these antigens increased to 100% up to 5 years of age. There was a significant correlation between RAST levels of rDer f 1 and rDer f 2 in these young children aged 0–1. IgE reactivities to four mutant proteins of rDer f 2, which have at least one amino acid substitution, were similarly examined in the asthmatic sera. IgE reactivity to D7A, in which Asp7 was replaced by Ala, was reduced to 30–60% compared to the rDer f 2. IgE binding to C8/119S, in which both Cys8 and Cysll9 were replaced by Ser, lacking a disulfíde bond between Cys8 and Cys119, was reduced almost to a background level at all ages. In contrast, A72L and A120L, in which Ala72 and Ala120 were substituted for Leu, respectively, almost retained the same IgE binding activity as the rDer f 2 at all ages. These results suggest that Der f 1 and Der f 2 are important antigens associated with early sensitization to house dust mite in young asthmatic children. In addition, the disulfide bond between Cys8 and Cys119 and the N-terminal region including the 7th amino acid residue are considered to maintain IgE epitopes of the Der f 2 allergen.