ELISA method for detection of mite allergens in barn dust: comparison with mite counts

Nanogold - IgY antibodies. An immunoconjugated for the detection of house dust mite (Dermatophagoides) allergens

Conjugation of avian IgY antibodies to nanosensors has been extensively explored for the diagnostics of virus and parasite infection, as well as for the detection of pharmaceutically and toxicologically relevant molecules. However, to date this strategy has only been minimally applied the detection of allergens. In this study, gold nanoparticles (GNPs) were conjugated to a polyvalent IgY antibodies raised against Dermatophagoides group I allergens. GNPs were synthesized by HAuCL₄ reduction using 1% trisodium citrate, and characterized them by absorption spectroscopy and transmission electron microscopy (TEM). The most stable immunoconjugates were obtained with 18-nm monodisperse GNPs and a minimal concentration of 12.5 μg/mL of IgY at pH 7.5. The immunoconjugate was capable of detecting up to 1.5 μg of a total Dermatophagoides farinae protein extract in an immuno-dot blot assay. This immunoreactant conjugate represents a new tool for the detection and control of indoor dust mite allergens.

[House dust mites allergens]

INTRODUCTION

House dust mite allergens from the Pyroglyphidae family are one of the most frequent and potent causes of allergic sensitatisation. Since 1988, molecular knowledge has increased considerably and structures and functions have been determined for most of them.

BACKGROUND

Of the 22 defined allergens, the major IgE-binding has been reported for groups 1 and 2 accounting for 40-60% of the anti-house dust mite titres. Der p 1, 2, 4, 5, 7 allergens account for about 80% of the IgE-response. Der p 4, 5, 7, 11, 14, 15 have a prevalence of sensitization of about 10% each. The IgE-binding to groups 3, 8, 10, 20 is low. Most of the allergens can be identified by amino-acid sequences and the tertiary structures of the major allergens have been solved. Most allergens are proteolytic enzymes: Der p1 for instance is a cysteine protease. Der p 2 has structural homology with MD-2, a co-receptor of the Toll-like receptor (TLR4) whose ligand is LPS. Knowledge of the structure of mite allergens has allowed better interpretation of cross-reactions between allergens from the same family or from more distant families.

CONCLUSIONS

From a practical point of view: the occurrence of multisensitisation is better explained and molecular epidemiology has allowed a better choice of allergen molecules useful for diagnosis. Finally, new concepts of immunotherapy based on genetically engineered hypoallergenic variants of major allergens, used alone or in combination, may lead to useful therapeutic approach.

Rapid method for the detection of storage mites in cereals: feasibility of an ELISA based approach

This paper describes the development of rapid immunodiagnostic tests for the detection of storage mite infestations in cereals and cereal products. The study's first phase (proof of concept) involved the production of a species-specific enzyme-linked immunoassay (ELISA) for the flour mite, Acarus siro (L.), a major pest of stored commodities. The specificity of this new assay was assessed against key stored product contaminants (13 species of mites of which three were predatory, five species of insects and five species of fungi) in the presence and absence of grain. The assay was species-specific (no cross-reactivity to other storage contaminants) and was unaffected by the presence of cereal antigens in the extract. In the study's second phase, species- and genera-specific ELISAs were developed for a range of key storage mite pests: the cosmopolitan food mite (Lepidoglyphus destructor), the grocers' itch mite (Glycyphagus domesticus), the grainstack mite (Tyrophagus longior), mites of the Tyrophagus and Glycyphagus generas, and all storage mites. All tests were demonstrably specific to target species or genera, with no cross-reactions observed to other storage pest contaminants or cereals. The final, validation phase, involved a comparative assessment of the species-specific A. siro and the genus-specific Tyrophagus ELISAs with the flotation technique using laboratory and field samples. Both ELISAs were quantitative (0-30 mites per 10 g wheat) and produced good comparative data with the flotation technique (A. siro r(2)=0.91, Tyrophagus spp. r(2)=0.99).

Mite fauna in the home and sensitivity to house-dust and storage mites

In search of potential new indoor allergen sources, all mites in dust from homes of 55 asthmatic children living in three climatic regions in Sweden were counted and identified by light microscope. Antibodies of the IgE class against three house-dust mites and three storage mites were measured in corresponding serum samples. Mites were found in all but two homes from the northernmost area, where levels also were lower than in the other regions. The highest mite densities were most often found in bedrooms (50%) and living rooms (40%). Mite density was increased in homes with high humidity and was higher in bungalows than in flats. House-dust mites predominated in the south and storage mites in the east central area, particularly in kitchens and bathrooms. Mite-density and IgE-antibody levels against house-dust mites were significantly associated. The same association applied to storage mites. Other species numbered around 100 mites/g dust in some homes. Microscopy helps to identify potentially important mites. Analysing home dust only for house-dust mites will underestimate mite exposure. Storage mites may be as relevant to sensitivity as house-dust mites. As other species occasionally were found in high numbers, their relevance should also be assessed.

Clinical and immunologic aspects of storage mite allergy

Exposure to storage (nonpyroglyphid) mites has been increasingly recognized as a cause of asthma and rhinitis. Several species have been identified in Europe; e.g., Lepidoglyphus destructor, Acarus farris/siro, Tyrophagus spp., Glycyphagus domesticus, and Blomia tjibodas. Blomia tropicalis, on the other hand, predominates in subtropical and tropical areas. Studies from several countries have shown that IgE-mediated allergy in rural populations is of considerable importance and that storage mites are major allergens. Since these mites are found in homes, especially in regions with damp housing conditions, urban populations are at risk of becoming sensitized. Therefore, sensitization is not restricted only to those with occupational exposure. Several major allergens from storage mites have been identified and characterized. There seems to be a limited allergenic cross-reactivity between storage- and house dust mites. Molecular cloning has demonstrated that the Group 2 allergens from storage mites (Lep d 2 and Tyr p 2) show more than 40% sequence identity with the Group 2 allergens from Dermatophagoides spp. The availability of a large number of recombinant dust mite allergens will make it possible to investigate their homology and the number of allergens required for the diagnosis and treatment of storage mite allergy.

Occurrence of mites in Norway and the rest of Scandinavia

This paper gives a faunistic review of mites that have been recorded in the indoor environment, particularly homes, barns, and stored products, in Norway and the other Scandinavian countries. Some preliminary results are given from unpublished investigations in Norway. Seven species of pyroglyphid mites have been recorded: Dermatophagoides pteronyssinus, D. microceras, D. farinae, D. evansi, Euroglyphus maynei, Gymnoglyphus longior, and Hirstia chelidonis. D. pteronyssinus was the predominant species, followed by D. microceras in Scandinavia and D. farinae in Denmark. D. evansi was detected in poultry houses in Norway. Lepidoglyphus destructor was the predominant species in barn dust, but large populations of Acarus, Tyrophagus, Tydeus, and Tarsonemidae also occurred. In humid homes, Glycyphagus domesticus was found in high numbers. The result of quantification of mites depends on the method for examination of dust. When one proposes limits for the concentration of mites in relation to risk of allergic sensitization and provocation of symptoms, reference should be made to a well-described method for sampling and analyzing dust. The number of mites should be given per area, not only per weight unit of dust. The number of mites per area indicates the number of mites in the home. The number of mites per weight unit of dust describes the concentration of mites in the vacuum cleaner.