IgE responsiveness to Dermatophagoides farinae in young asthmatic children: IgE binding study using recombinant allergens of Der f1, Der f2 and mutant proteins of Der f2.

IgE reactivities to two recombinant (r) allergens, rDer f1 and rDer f2, 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 f1 and rDer f2 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 f1 and rDer f2 in these young children aged 0-1. IgE reactivities to four mutant proteins of rDer f2, 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 f2. IgE binding to C8/119S, in which both Cys8 and Cys119 were replaced by Ser, lacking a disulfide 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 f2 at all ages. These results suggest that Der f1 and Der f2 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 f2 allergen.