Lack of human IgE cross-reactivity between mite allergens Blo t 1 and Der p 1

Background: The group 1 mite allergens are the most significant indoor allergens and they belong to the papain-like cysteine protease family. To date there is only one published report on the isolation and characterization of group 1 allergens from Blomia tropicalis mites. The aims of the study are to determine the cross-reactivity between group 1 allergens and to evaluate their clinical importance in allergic patients. Methods: The full-length Blo t 1 gene was obtained by SMART(TM) RACE cDNA amplification method using gene-specific primers. The sequence alignment was performed using LOOK followed by three-dimensional homology modeling. The cDNA was expressed in Pichia pastoris as a secretory protein. Identification of native Blo t 1 in crude mite and spent mite medium extracts was done by Western immunoblot using monoclonal antibody. Allergenicity of recombinant Blo t 1 and native Der p 1 was examined by human IgE ELISA with 80 asthmatic sera. Results: The cDNA sequence consists of 1105 base pairs, including 5'- and 3'-untranslating regions, encoding an open reading frame of 330 amino acid residues. The predicted molecular weight of the deduced protein was approximately 38 kDa. Blo t 1 shared 53 and 34% nucleotide and amino acid, respectively, sequence homology with Der p 1. Native Blo t 1 was detected in both crude mite and spent mite medium extracts, and its estimated molecular weight was about 26 kDa. The recombinant Blo t 1 reacted positively with IgE in 90 and 65% of sera from asthmatic children and adults, respectively, indicating that it is a major allergen. The correlation of human IgE reactivity between Blo t 1 and Der p 1 was low in these sera. Conclusion: The full-length cDNA encoding group 1 Blomia tropicalis mite allergen (designated as Blo t 1) has been characterized and expressed from local mites in Singapore. This fecal allergen showed high frequency of human IgE reactivity with asthmatic sera in the tropics and there was a low correlation of IgE reactivity between Blo t 1 and Der p 1.