[Blomia tropicalis: A house dust mite in the tropics]

What's childhood asthma in French Guiana? A cohort study based on children referred for allergology consultations at the Cayenne hospital center

Background

Asthma is a multifactorial chronic disease, whose most frequent etiology is allergy, especially to Blomia tropicalis. In French Guiana, the childhood prevalence of Blomia T sensitization is unkwown. The aim of this study was to determine the proportion of sensitization to Blomia T and other mites in asthmatic children, and to describe the characteristics of childhood asthma in French Guiana.

Methods

A retrospective cohort study focused on children from 0 to 18 years of age, followed for asthma at the Department of Pediatrics of the Cayenne Hospital Center in French Guiana. All asthmatic children followed by the same paediatric allergist were systematically skin-tested with Bt total extract, and Bt-specific IgE tests were additionally performed to confirm specific sensitization. All follow-up variables were collected from medical records. The outcome was sensitization to Blomia tropicalis and other allergens, and the explanatory variables were those of asthma follow-up. Patients were categorized into Blomia tropicalis sensitization yes/no. Logistic regression analysis was used to assess the relationship between follow-up variables and the outcome.

Results

302 patients were followed: 177 cases of allergic rhinitis, 135 allergic conjunctivitis, 105 atopic dermatitis, 153 food allergy, and 14 cases of drug allergy. Poly-allergy (respiratory, food, skin, and medicinal) was present in 239 children. There were 158 children followed for asthma, of whom 103 (65%) were sensitized to Blomia tropicalis. The median age of the asthmatic children sensitized to Blomia tropicalis was 7 years, and 3 years for those who were not sensitized (p < 0.001). Among the girls (n = 58), 67% were sensitized to Blomia; 97 (92%) asthmatic children co-sensitized to Blomia tropicalis, Dermatophagoides pteronyssinus, and Dermatophagoides farinae. Multivariate analysis showed that the childhood asthma in French Guiana is characterized by a median age of 7 years (p < 0.001), a high prevalence of Blomia tropicalis (p < 0.001), co-sensitization to other mites (p < 0.001), and a high prevalence of co-sensitization to cockroaches (p = 0.006). The area under the ROC curve was close to 0.9, confirming the quality of our model.

Conclusion

In French Guiana, asthma is characterized by a high prevalence of Blomia tropicalis sensitization.

[Allergenic and chemical pollutants of indoor environments and asthma: Characterization, assessment and eviction]

The environment of an asthmatic patient can contain numerous sources of pollutants that degrade the quality of indoor air and have major repercussions on the occurrence and control of asthma. Assessment and improvement of the quality of indoor air should be assigned a major role in pneumology and allergology consultations. Characterization of an asthmatic's environment entails a search for biological pollutants with mite allergens, mildew, and allergens resulting from the proximity of pets. It is important to evaluate the chemical pollution represented by exposure to volatile organic compounds, which are increasingly present in our lodgings. Active or second-hand smoking must in all circumstances be sought out and quantified. Assessment of the environment is mediated by several methods, of which the application depends not only on the pollutant sought out, but also on enzyme-linked immunosorbent assay (ELISA), which has an essential role in quantification of biological pollutants. Attempts at expulsion of the different indoor environment pollutants is mediated by indoor environment advisors, whose efforts are aimed at obtaining reliable evaluation and control of indoor air. Implemented as a form of tertiary prevention, their methods are conducive to improved asthma control, in adults as well as children.

IgE and IgG4 Epitopes of Dermatophagoides and Blomia Allergens before and after Sublingual Immunotherapy

Sublingual immunotherapy (SLIT) is used worldwide to treat house dust mites (HDM) allergy. Epitope specific immunotherapy with peptide vaccines is used far less, but it is of great interest in the treatment of allergic reactions, as it precludes the drawbacks of allergen extracts. The ideal peptide candidates would bind to IgG, blocking IgE-binding. To better elucidate IgE and IgG4 epitope profiles during SLIT, sequences of main allergens, Der p 1, 2, 5, 7, 10, 23 and Blo t 5, 6, 12, 13, were included in a 15-mer peptide microarray and tested against pooled sera from 10 patients pre- and post-1-year SLIT. All allergens were recognized to some extent by at least one antibody isotype and peptide diversity was higher post-1-year SLIT for both antibodies. IgE recognition diversity varied among allergens and timepoints without a clear tendency. Der p 10, a minor allergen in temperate regions, was the molecule with more IgE-peptides and might be a major allergen in populations highly exposed to helminths and cockroaches, such as Brazil. SLIT-induced IgG4 epitopes were directed against several, but not all, IgE-binding regions. We selected a set of peptides that recognized only IgG4 or were able to induce increased ratios of IgG4:IgE after one year of treatment and might be potential targets for vaccines.

Efficacy and safety of subcutaneous immunotherapy with a mixture of glutaraldehyde-modified extracts of Dermatophagoides pteronyssinus, Dermatophagoides farinae , and Blomia tropicalis

Background

Allergen Immunotherapy (AIT) is an effective treatment of allergic respiratory diseases induced by the inhalation of house dust mite allergens.

Objectives

To evaluate the efficacy and safety of glutaraldehyde polymerized allergen extracts using a mixture of Dermatophagoides pteronyssinus, D. farinae and Blomia tropicalis in mite allergic individuals residing in Colombia.

Methods

Two hundred and fifty (250) patients with allergic rhinoconjunctivitis with, or without asthma and sensitized to D. pteronyssinus, D. farinae and B. tropicalis were included. A glutaraldehyde-modified extract containing a mixture of D. pteronyssinus, D. farinae and B. tropicalis was employed, using a cluster up-dosing schedule followed by a monthly maintenance dose. The primary endpoints to evaluate the clinical impact were the Combined Symptom and Medication Scores (CSMS) for allergic rhinitis, the Asthma Control Test (ACT) and the reduction in medication consumption.

Results

Significant improvement was found after 3 months of treatment regarding CSMS (p < 0.0001) and ACT (p < 0.0001). Additionally, a significant decrease in medication consumption was found after 3 months of treatment (p < 0.0001). Adverse reactions, either local or systemic were mild and no severe reactions related to the vaccines were observed.

Conclusion

After 12 months of allergen immunotherapy, glutaraldehyde-modified mixture of D. pteronyssinus, D. farinae and B. tropicalis proved to be safe and effective in the treatment of patients with rhinoconjunctivitis with or without asthma due to allergy to mites.

Comparative Genomics Reveals Insights into the Divergent Evolution of Astigmatic Mites and Household Pest Adaptations

Highly diversified astigmatic mites comprise many medically important human household pests such as house dust mites causing ∼1–2% of all allergic diseases globally; however, their evolutionary origin and diverse lifestyles including reversible parasitism have not been illustrated at the genomic level, which hampers allergy prevention and our exploration of these household pests. Using six high-quality assembled and annotated genomes, this study not only refuted the monophyly of mites and ticks, but also thoroughly explored the divergence of Acariformes and the diversification of astigmatic mites. In monophyletic Acariformes, Prostigmata known as notorious plant pests first evolved, and then rapidly evolving Astigmata diverged from soil oribatid mites. Within astigmatic mites, a wide range of gene families rapidly expanded via tandem gene duplications, including ionotropic glutamate receptors, triacylglycerol lipases, serine proteases and UDP glucuronosyltransferases. Gene diversification after tandem duplications provides many genetic resources for adaptation to sensing environmental signals, digestion, and detoxification in rapidly changing household environments. Many gene decay events only occurred in the skin-burrowing parasitic mite Sarcoptes scabiei. Throughout the evolution of Acariformes, massive horizontal gene transfer events occurred in gene families such as UDP glucuronosyltransferases and several important fungal cell wall lytic enzymes, which enable detoxification and digestive functions and provide perfect drug targets for pest control. This comparative study sheds light on the divergent evolution and quick adaptation to human household environments of astigmatic mites and provides insights into the genetic adaptations and even control of human household pests.

New variants in NLRP3 inflammasome genes increase risk for asthma and Blomia tropicalis-induced allergy in a Brazilian population

Atopic asthma is a chronic lung disease of lower airways caused mainly due to action of T-helper (Th) 2 type cytokines, eosinophilic inflammation, mucus hypersecretion and airway remodelling. Interleukin (IL)-33 increases type 2 immunity polarization in airway playing critical role in eosinophilic asthma. On the other hand, NLRP3 inflammasome activation results in the release of caspase-1 (Casp-1) which, in its turn, promotes IL-33 inactivation. Recent studies have shown associations between NLRP3 variants and inflammatory diseases. However, no study with genes in NLRP3 inflammassome route has been conducted so far with asthma and atopy in any population to date. Blood samples were collected from 1246 asthmatic and non-asthmatic children. Associations were tested for single nucleotide polymorphism (SNP)s in NLRP3 and CASP1 with asthma and markers of atopy and in cultures stimulated with Blomia tropicalis (Bt) mite crude extract. The T allele of rs4925648 (NLRP3) was associated with increased asthma risk (OR 1.50, P = 0.005). In addition, the T allele of rs12130711 polymorphism, whithin the same gene, acted as a protector factor for asthma (OR 0.78, P = 0.038). On the other hand, the C allele of rs4378247 NLRP3 variant was associated with lower levels of IL-13 production when peripheral blood cells were stimulated with Bt (OR 0.39, P = 4E-04). In addition, the greater the number of risk alleles in IL33/NLRP3/CASP1 route the greater was the risk for asthma. The T allele of rs7925706 CASP1 variant was also associated with increased risk for asthma (OR 1.47, P = 0.008). In addition, this same allele increased the eosinophil counts in blood (mm3) in asthmatic individuals compared with non-asthmatic (P = 0.0004). These results suggest that NLRP3 and CASP1 polymorphisms may be associated with susceptibility for asthma and markers of atopy in our population.

A hybrid of two major Blomia tropicalis allergens as an allergy vaccine candidate

Introduction

Allergen‐specific immunotherapy (AIT) represents a curative approach for treating allergies. In the tropical and subtropical regions of the world, Blomia tropicalis (Blo t 5 and Blo t 21) is the likely dominant source of indoor allergens.

Aim

To generate a hypoallergenic Blo t 5/Blo t 21 hybrid molecule that can treat allergies caused by B tropicalis.

Methods

Using in silico design of B tropicalis hybrid proteins, we chose two hybrid proteins for heterologous expression. Wild‐type Blo t 5/Blo t 21 hybrid molecule and a hypoallergenic version, termed BTH1 and BTH2, respectively, were purified by ion exchange and size exclusion chromatography and characterized by physicochemical, as well as in vitro and in vivo immunological, experiments.

Results

BTH1, BTH2 and the parental allergens were purified to homogeneity and characterized in detail. BTH2 displayed the lowest IgE reactivity that induced basophil degranulation using sera from allergic rhinitis and asthmatic patients. BTH2 essentially presented the same endolysosomal degradation pattern as the shortened rBlo t 5 and showed a higher resistance towards degradation than the full‐length Blo t 5. In vivo immunization of mice with BTH2 led to the production of IgG antibodies that competed with human IgE for allergen binding. Stimulation of splenocytes from BTH2‐immunized mice produced higher levels of IL‐10 and decreased secretion of IL‐4 and IL‐5. In addition, BTH2 stimulated T‐cell proliferation in PBMCs isolated from allergic patients, with secretion of higher levels of IL‐10 and lower levels of IL‐5 and IL‐13, when compared to parental allergens.

Conclusions and Clinical Relevance

BTH2 is a promising hybrid vaccine candidate for immunotherapy of Blomia allergy. However, further pre‐clinical studies addressing its efficacy and safety are needed.

Proteomic Analysis Reveals Allergen Variability among Breeds of the Dust Mite Blomia tropicalis

BACKGROUND

The dawn of the "omics" technologies has changed allergy research, increasing the knowledge and identification of new allergens. However, these studies have been almost restricted to Dermatophagoides spp. Although Blomia tropicalis has long been established as a clinically important source of allergens, a thorough proteomic characterization is still lacking for this dust mite.

OBJECTIVE

To increase knowledge of B. tropicalis allergens through proteomic analysis.

METHODS

Eleven in-bred lineages of B. tropicalis were obtained from 11 unique different pregnant females. Their somatic extracts were analyzed and compared with a commercially available extract by liquid chromatography tandem mass spectrometry (LC-MS/MS).

RESULTS

Considerable differences in the protein expression profiles were found among the breeds, and most of them displayed higher expression levels of major allergens than the commercially available extract. Blo t 2 was the most prominent allergenic protein in the analyzed extracts. Six identified allergens and 14 isoforms have not yet been recognized by IUIS. Conversely, 3 previously recognized B. tropicalis allergens were not found.

CONCLUSIONS

The clear impact of inbreeding on allergen content shown by our study leads us to conclude that the quantification and/or identification of allergens from in-bred lines should be routinely considered for mite cultivation in order to select breeds with higher amounts of major allergens. In this sense, LC-MS/MS may be a useful method to achieve this quality control for research and commercial purposes.

Socio-environmental profile of child and adolescents sensitized by house dust mite in northeast of Brazil

INTRODUCTION

The association regarding the atopic sensitization to mite aeroallergens and the socio-environmental features is still inconsistent.

OBJECTIVES

We analyzed the role played by socioeconomic and environmental factors in the prevalence of sensitization to house dust mite (HDM) allergens, and associated with the risk of developing asthma symptoms.

PATIENTS AND METHODS

This is a case-control study conducted with 108 patients, aged 1-17. We inquired about family habits, socioeconomic and environmental features. We applied the International Study of Asthma and Allergies in Childhood questionnaire.

RESULTS

We observed patients sensitized to all HDM tested, Derp (42%), Derf (37%) and Blot (33%). Middle family income (OR: 2.74; CI95%: 1.127-6.684), exposure to dog (OR: 3.758, CI95%: 1.127-6.684) and artificial climatization (OR: 4.319, CI95%: 1.398-13.348) were associated with sensitization to Derp. We also observed protective factors, such as sharing of dormitories, washing cycle for bedspreads and the presence of basic sanitation. An increased risk of sensitization to Derf was associated with Blot sensitization (OR: 3.172, CI95%: 1.083-9.292) and presence of mold on the walls (OR: 3.095, CI95%: 1.063-9.008). A protective factor was dormitory sharing. For sensitization to Blot, we observed an increase in the risk associated with Derp sensitization (OR: 3.462, CI95%: 1.191-10.061) and exposure to dog (OR: 3.255, CI95%: 0.987-10.736). In addition, sensitization to Blot increases the risk of developing asthma symptoms (OR: 2.732, CI95%: 0.981-7.606).

CONCLUSION

Our data show distinct sociodemographic and environmental relations that lead to HDM sensitization and increased probability of development of allergic diseases.