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

Gao Y.F., Wang D.Y., Ong T.C., Tay S.L., Yap K.H., Chew F.T.


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


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


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.


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 alpha-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 1(1/2) 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.


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.

J. Allergy Clin. Immunol. 120:105-112(2007) [PubMed] [Europe PMC]

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