Fong Cheng Yi

Identification of shared and unique immunoglobulin E epitopes of the highly conserved tropomyosins in Blomia tropicalis and Dermatophagoides pteronyssinus

Background Tropomyosin belongs to a class of highly conserved proteins in invertebrates and vertebrates. The invertebrate tropomyosins are allergenic in man with high IgE cross‐reactivity and have been therefore referred to as pan‐allergens.

Prevalence and distribution of indoor allergens in Singapore

Background and aims Immediate hypersensitivity to indoor allergens is known to be associated with allergic asthma. This study evaluated the prevalence and distribution of six indoor allergens in 956 dust samples obtained from homes, childcare centres, schools, and a hospital in tropical Singapore. Seasonality of mite allergens was also assessed.

Parvalbumin : the major tropical fish allergen

Fish allergy is common in countries where consumption is high. Asian nations are amongst the world’s largest consumers of fish but the allergen profiles of tropical fish are unknown. This study sought to evaluate the allergenicity of four commonly consumed tropical fish, the threadfin (Polynemus indicus), Indian anchovy (Stolephorus indicus), pomfret (Pampus chinensis) and tengirri (Scomberomorus guttatus). Immunoglobulin E (IgE) cross‐reactivity with parvalbumin of cod fish (Gad c 1), the major fish allergen, was also studied. Detection of tropical fish and cod specific‐IgE was performed by UniCap assay, and skin prick tests were also carried out. The IgE‐binding components of tropical fish were identified using IgE immunoblot techniques, and cross‐reactivity with Gad c 1 was assessed by ELISA inhibition and IgE immunoblot inhibition. Clinically, nine of 10 patients studied were allergic to multiple fish. All patients exhibited detectable specific‐IgE to cod fish (10 of 10 skin prick test positive, eight of 10 UniCap assay positive) despite lack of previous exposure. The major allergen of the four tropical fish was the 12‐kDa parvalbumin. IgE cross‐reactivity of these allergens to Gad c 1 was observed to be moderate to high in the tropical fish studied. Parvalbumins are the major allergens in commonly consumed tropical fish. They are cross‐reactive with each other as well as with Gad c 1. Commercial tests for cod fish appear to be sufficient for the detection of tropical fish specific‐IgE.

The Blomia tropicalis Allergens

Blomia tropicalis allergens are the most important mite allergens in tropical regions. Most of them only have 30-40% sequence identity with their Dermatophagoides counterparts and they share low IgE cross reactivity and exhibit different immunobiology. Unlike the pyroglyphid counterparts, Blo t 5 is the major allergen whereas Blo t 1 only has modest allergenicity.

Identification of the major allergenic components in Blomia tropicalis and the relevance of the specific IgE in asthmatic patients

BACKGROUND Blomia tropicalis has been reported to be a clinically important allergen in house dust. High prevalence of sensitization to B. tropicalis has been noted in asthmatic patients in Taiwan; however, the allergenic components and its impact on asthmatic patients remain to be clarified. OBJECTIVE To analyze the prevalence of IgE against B. tropicalis and each allergenic component in asthmatic patients. METHODS A series of recombinant allergenic components were used for skin tests. The B. tropicalis specific IgE in the serum were measured using the Pharmacia CAP System and immunoblot analysis. RESULTS A total of 131 patients were included in this study: 44% of these 131 patients were allergic to B. tropicalis, 43% of the 80 B. tropicalis-sensitive patients were allergic to Blo t 5, and 75% of the 65 Blo t 5-sensitive patients were allergic to Blo t 5 fragment 3 (Blo t 5 70-117). The sera IgE binding activity to B. tropicalis was repeatedly tested after Dermatophagoides pteronyssinus absorption, and results showed that most patients were concurrently sensitized to D. pteronyssinus and B. tropicalis. In addition, in 2 (18%) of 11 patients, the B. tropicalis sensitization was caused by the cross-reactivity of D. pteronyssinus. CONCLUSION A high prevalence of B. tropicalis sensitization was detected in our asthmatic patients, and most of them were concurrently sensitized to D. pteronyssinus and B. tropicalis. The major allergenic component and its IgE binding fragments in Blo t 5 have been identified. These allergenic components can be used for the allergenic determination in B. tropicalis and for further immunotherapy.

Molecular Cloning of Blomia tropicalis Allergens - A Major Source of Dust Mite Allergens in the Tropics and Subtropics

Allergic asthma, rhinitis, rhinoconjunctivitis and atopic dermatitis are the most common allergic disorders that are caused by the house dust mite (HDM). Beside pyroglyphid mites, the clinical importance of non-pyroglyphid mites has also been increasingly recognized in the recent years. Blomia tropicalis is the most important and ubiquitous mite species in tropical and subtropical regions of the world. Well-standardized and characterized allergens are essential for the diagnosis and therapy of house dust mite allergy as well as for the study of the pathophysiology of allergic disease. With the introduction of molecular biology, a number of house dust mite allergens were obtained by cloning the genes encoding the allergens. To date, seven allergens from Blomia tropicalis have been identified and characterized. Among these, Blo t 5, with unknown function, is the major allergen of Blomia tropicalis, with up to 92% of allergic patients sensitized to it. Native Blo t 5 has been purified and shown to consist of multiple isoforms. With advancing knowledge of these specific allergens, it is anticipated that targeted, effective, diagnostic, efficacious and safe therapeutic modalities would be developed.

Quantification of Blo t 5 in mite and dust extracts by two-site ELISA.

Background:  Blomia tropicalis is an important mite species in the tropical and sub‐tropical regions of the world. Blo t 5 is the major allergen with up to 70% sensitization rates in B. tropicalis allergic populations.

Dust mite infestation of flour samples

Background:  Ingestion of flour contaminated with dust mite may trigger severe anaphylaxis in tropical and sub‐tropical regions.

Immunoglobulin E reactivity of native Blo t 5, a major allergen of Blomia tropicalis

Background Blo t 5 is a major allergen of Blomia tropicalis and its complementary DNA (cDNA) has been expressed in both prokaryotic and eukaryotic expression systems. Although the recombinant Blo t 5 has been well characterized, relatively less is known about its native counterparts and the allergenicity comparison of the native and recombinant Blo t 5 allergens has not been reported.