Sequence information has been obtained from 5 cDNA clones encoding the major house dust mite allergen Der p I, including one which codes for the full length preproenzyme form of the molecule. All translated sequences were unique with 1–3 differences between each clone. 4/5 of the substitutions found were to residues found in Der f l and two positions had a substitution in more than one clone. The polymorphisms included residues already described to be in T cell epitopes, so as well as being necessary to consider them in the construction of synthetic allergens, the substitutions will be important for the interpretation of experimental and genetic studies.

The major mite allergen Der p II shows marked resistance to denaturation and is expressed from cDNA in bacteria with almost all of its IgE binding activity. Despite these properties, the IgE binding activity appears to be dependent on maintaining the complete primary structure. Random fragment libraries of cDNA, able to code for up to 93 of the 129 amino acid residue protein, did not express IgE binding peptides. Large overlapping peptides 1-69, 69-129 and 42-117 expressed as the fusions from the glutathione transferase of pGEX vectors only had binding activity with IgE in 15 out of 57 sera, and this was typically weak. Sera from children with atopic dermatitis bound IgE in seven out of eight cases but this was also weak compared with their strong reactivity to intact recombinant Der p II. The inability of such large peptides to form IgE binding structures suggests that the antigenic determinants of Der p II are highly conformational and restricted.

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