Frequent IgE recognition of Blomia tropicalis allergen molecules in asthmatic children and young adults in equatorial Africa

Abstract

Background: Asthma is not well investigated in equatorial Africa and little is known about the disease-associated allergen molecules recognized by IgE from patients in this area. The aim was to study the molecular IgE sensitization profile of asthmatic children and young adults in a semi-rural area (Lambaréné) of an equatorial African country (Gabon), to identify the most important allergen molecules associated with allergic asthma in equatorial Africa.

Methods: Fifty-nine asthmatic patients, mainly children and few young adults, were studied by skin prick testing to Dermatophagoides pteronyssinus (Der p), D. farinae (Der f), cat, dog, cockroach, grass, Alternaria and peanut. Sera were obtained from a subset of 35 patients, 32 with positive and 3 with negative skin reaction to Der p and tested for IgE reactivity to 176 allergen molecules from different allergen sources by ImmunoCAP ISAC microarray technology and to seven recombinant Blomia tropicalis (Blo t) allergens by IgE dot blot assay.

Results: Thirty-three of the 59 patients (56%) were sensitized to Der p and 23 of them (39%) were also sensitized to other allergen sources, whereas 9 patients (15%) were only sensitized to allergen sources other than Der p. IgE serology analyses (n=35) showed high IgE-binding frequencies to the Blo t allergens Blo t 5 (43%), Blo t 21 (43%) and Blo t 2 (40%), whereas the Der p allergens rDer p 2, rDer p 21 and rDer p 5 (34%, 29% and 26%) were less frequently recognized. Only few patients showed IgE reactivity to allergens from other allergen sources, except to allergens containing carbohydrate determinants (CCDs) or to wasp venom allergens (i.e., antigen 5).

Conclusion: Our results thus demonstrate that IgE sensitization to mite allergens is very prevalent in asthmatics in Equatorial Africa with B. tropicalis allergen molecules representing the most important ones associated with allergic asthma.

Keywords: Blomia tropicalis; Dermatophagoides; allergen microarray; allergens; allergy; asthma; equatorial Africa.

Figure 1

Flowchart of investigations in patients included in the study.

Figure 2

Frequencies of skin prick reactions to different allergen extracts. Frequencies of reactivity (y-axes) to cat extract, dog extract, D. pteronyssinus extract, D. farinae extract, grass pollen extract and peanut extract cockroach extract and Alternaria extract (x-axes) are shown (A), for all 59 patients, (B), for the 35 patients included in the study. For cockroach extract and Alternaria extract, frequencies of reactivity are shown (A), for the 49 patients and (B), for the 29 patients tested with these extracts.

Figure 3

Frequencies and intensities of IgE reactivity to individual mite allergens. Frequencies of IgE reactivity and specific IgE levels (white, ISU = 0.1-0.99; grey, ISU 1-14.99; black, ISU > 14.99) (y-axis) to 16 mite allergens (x-axis) determined by micro-array analysis are shown for the 35 patients of the study.

Figure 4

Frequencies and intensities of IgE reactivity to individual allergens from different allergen sources. Frequencies of IgE reactivity and specific IgE levels (white, ISU = 0.1-0.99; grey, ISU 1-14.99; black, ISU > 14.99) (y-axis) to individual allergens from (A), insects, (B), animals, (C), grasses, (D), trees, (E) weeds, (F), latex, (G), mould, (H), non-plant derived food and (I), plant derived food (x-axis) as determined by micro-array are shown for the 35 patients with IgE serology.

Figure 5

Concordances and discordances between skin prick tests and micro-array analysis. The number of patients (y-axis) with concordant results (left bar) or discordant results in skin prick tests and micro-array (central bar, positive SPT >3mm/negative ISAC, right bar, negative SPT/positive micro-array) for D. pteronyssinus, grass, cockroach, cat, dog and peanut (x-axis) are shown for the 35 patients of the study and for cockroach for the 29 patients tested by SPT.

Figure 6

IgE-reactivity to Blomia tropicalis allergens. Dot blotted Blomia tropicalis allergens (rBlo t 2, rBlo t 5, rBlo t 8, rBlo t 10, rBlo t 12, rBlo t 13 and rBlo t 21) and BSA were tested for IgE-reactivity with sera from the 35 asthmatic patients of the study (1-35) and serum from a non-allergic individual (NC).

Figure 7

Frequencies of IgE sensitization and IgE levels to Blo t 5 and house dust mite allergens (x-axis) (ISU = 0.1-0.99; ISU 1-14.99; ISU > 14.99) (y-axis) in patients with different asthma severity scores, 2-4 (left columns) or <2 (right columns).