Identification and characterisation of two allergens from the dust mite Acarus siro, homologous with fatty acid-binding proteins

• <b>Background:</b> Dust mites are a major cause of allergic disease worldwide. The dust mite <i>Acarus siro</i> is an inducer of occupational allergy among farmers, but sensitisation has also been found in non–farming populations. <b>Methods:</b> A degenerate primer was designed to the N–terminal amino acid sequence of a 15–kD IgE–binding protein in <i>A. siro</i> extract. The cDNA sequence was obtained by using reverse transcriptase polymerase chain reaction, standard cloning and sequencing techniques. The protein was expressed in <i>Escherichia coli</i> with a 6–histidine tag at its C–terminus. Immunoblotting of the recombinant protein and whole extract was performed using patient sera. <b>Results and conclusion:</b> 15 and 17–kD allergens were identified in a fraction of <i>A. siro</i> extract. The cDNA of the 15–kD allergen was isolated, cloned and sequenced and the allergen was expressed as a recombinant protein. The calculated molecular weight of the cDNA–encoded protein is 14.2 kD. The predicted amino acid sequence has one potential N–glycosylation site at position 4–6 and a cytosolic fatty acid–binding protein signature at position 5–22. The protein has 64% sequence identity with Blo t 13, an allergen from the dust mite <i>Blomia tropicalis</i>, as well as homology with several other fatty acid–binding proteins (FABPs) from different organisms. The allergen was named Aca s 13 and was recognised strongly by 3 of 13 (23%) of the subjects investigated. The amino acid sequence of the 17–kD protein was partly determined and it also showed high sequence homology with Blo t 13 and FABPs.

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