Identification and characterization of a novel allergen from Blomia tropicalis: Blo t 21

Background

Allergenic components from Blomia tropicalis are important triggers of allergies in the tropics.

Objective

We sought to identify and characterize a novel allergen, Blo t 21, from B tropicalis.

Methods

Blo t 21 was initially identified from an expressed sequence tag database generated from a B tropicalis cDNA library. Allergenicity of this antigen was examined by means of skin prick testing, ELISA, and IgE immuno-dot blotting. We evaluated whether Blo t 21 and Blo t 5 were cross-reactive by using IgE inhibition ELISAs.

Results

Blo t 21, a 129-amino-acid protein sharing 39% identity with Blo t 5, is a product of a single-copy gene. It has an α-helical secondary structure and localizes to midgut and hindgut contents of B tropicalis, as well as fecal particles. Positive responses to Blo t 21 were shown in 93% (40/43) by means of ELISA and 95% (41/43) by means of skin prick testing when assayed in 43 adult patients with ongoing persistent allergic rhinitis. However, sera of 494 consecutive individuals attending outpatient allergy clinics over 1½ years showed 57.9% (286/494) had positive responses to Blo t 21. Although the majority (>75%) of sensitized individuals were cosensitized to both Blo t 5 and Blo t 21, these 2 allergens had a low-to-moderate degree of cross-reactivity.

Conclusion

Blo t 21 is a major allergen in B tropicalis that is not highly cross-reactive to Blo t 5, despite sharing some sequence and structural identity.

Clinical implications

Blo t 21, representing a new group of allergens, is an important B tropicalis allergen.

Key words: Dust mite, Blomia tropicalis, allergen, IgE binding, cross-reactivity, immunolocalization, genomic organization

Abbreviations used: CD, Circular dichroism, EST, Expressed sequence tagging, ORF, Open reading frame, SPT, Skin prick test