Allergy to Mus m 1: Allergy to Mus m 1: A review of structural, and immunological features

A review in analytical progress for house dust mite allergens

House dust mite (HDM) allergens are one of the most important causes of allergenic diseases in the indoor environment. The World Health Organization (WHO) has defined risk thresholds for Group I HDM allergens as a concentration of 2 and 10 μg/mL in dust for producing asthma risk and polar asthma attacks, respectively. Continuing exposure to high concentrations of HDM allergens greatly increases the risk of developing allergic diseases. Therefore, it's necessary to determine the exposure levels of HDM allergens to estimate the risk. So, various approaches have been developed to directly or indirectly detect HDM allergens in the environment. This paper overviews the developmental progress of HDM allergen detection and introduces the principle of HDM allergen detection methods, including semi-quantitative radioallergosorbent test (RAST), ACAREX test, dot immunobinding assay (DIBA), radioimmunoassay (RIA) which combines the high sensitivity and accuracy, enzyme-linked immunosorbent assay (ELISA) with high accuracy, fluorescent multiple arrays which can simultaneously detect multiple HDM allergens, polymerase chain reaction (PCR), and liquid chromatograph-mass spectrometer (LC-MS) with high sensitivity and accuracy. The paper provides an overall understanding of the development of HDM allergen detection methods and guidance for choosing an appropriate method to detect HDM allergens.

Role of Small Molecule Ligands in IgE-Mediated Allergy

PURPOSE OF REVIEW

A significant fraction of allergens bind small molecular ligands, and many of these compounds are classified as lipids. However, in most cases, we do not know the role that is played by the ligands in the allergic sensitization or allergic effector phases.

RECENT FINDINGS

More effort is dedicated toward identification of allergens' ligands. This resulted in identification of some lipidic compounds that can play active immunomodulatory roles or impact allergens' molecular and allergic properties. Four allergen families (lipocalins, NPC2, nsLTP, and PR-10) are among the best characterized in terms of their ligand-binding properties. Allergens from these four families are able to bind many chemically diverse molecules. These molecules can directly interact with human immune system and/or affect conformation and stability of allergens. While there is more data on the allergens and their small molecular ligands, we are just starting to understand their role in allergy.

Perspectives of Proteomics in Respiratory Allergic Diseases

Proteomics in respiratory allergic diseases has such a battery of techniques and programs that one would almost think there is nothing impossible to find, invent or mold. All the resources that we document here are involved in solving problems in allergic diseases, both diagnostic and prognostic treatment, and immunotherapy development. The main perspectives, according to this version, are in three strands and/or a lockout immunological system: (1) Blocking the diapedesis of the cells involved, (2) Modifications and blocking of paratopes and epitopes being understood by modifications to antibodies, antagonisms, or blocking them, and (3) Blocking FcεRI high-affinity receptors to prevent specific IgEs from sticking to mast cells and basophils. These tools and targets in the allergic landscape are, in our view, the prospects in the field. However, there are still many allergens to identify, including some homologies between allergens and cross-reactions, through the identification of structures and epitopes. The current vision of using proteomics for this purpose remains a constant; this is also true for the basis of diagnostic and controlled systems for immunotherapy. Ours is an open proposal to use this vision for treatment.

Component-Resolved Diagnosis Based on a Recombinant Variant of Mus m 1 Lipocalin Allergen

Exposure to the Mus m 1 aeroallergen is a significant risk factor for laboratory animal allergy. This allergen, primarily expressed in mouse urine where it is characterized by a marked and dynamic polymorphism, is also present in epithelium and dander. Considering the relevance of sequence/structure assessment in protein antigenic reactivity, we compared the sequence of the variant Mus m 1.0102 to other members of the Mus m 1 allergen, and used Discotope 2.0 to predict conformational epitopes based on its 3D-structure. Conventional diagnosis of mouse allergy is based on serum IgE testing, using an epithelial extract as the antigen source. Given the heterogeneous and variable composition of extracts, we developed an indirect ELISA assay based on the recombinant component Mus m 1.0102. The assay performed with adequate precision and reasonable diagnostic accuracy (AUC = 0.87) compared to a routine clinical diagnostic test that exploits the native allergen. Recombinant Mus m 1.0102 turned out to be a valuable tool to study the fine epitope mapping of specific IgE reactivity to the major allergen responsible for mouse allergy. We believe that advancing in its functional characterization will lead to the standardization of murine lipocalins and to the development of allergen-specific immunotherapy.

Diversity and complexity of mouse allergens in urine, house dust, and allergen extracts assessed with an immuno-allergomic approach

BACKGROUND

Mouse allergy is an important cause of indoor asthma and allergic rhinoconjunctivitis. The major mouse allergen, Mus m 1, is a complex of homologous pheromone-binding lipocalins called major urinary proteins (MUPs).

METHODS

We analyzed the proteome of MUPs in mouse urine, commercial mouse epithelial extracts, and environmental samples using several approaches. These include as follows: two-dimensional electrophoresis and immunoblotting; liquid chromatography-high-resolution mass spectrometry (LC/HRMS); multiple reaction monitoring (MRM) mass spectrometry; and LC/HRMS analysis of glycans at the N-66 residue of MUP3.

RESULTS

Albumin is predominant in the extracts, while MUPs are predominant in urine. LC/HRMS of 4 mouse allergen extracts revealed surprising heterogeneity. Of 22 known mouse MUPs, only 6 (MUP3, MUP4, MUP5, MUP13, MUP20, and MUP21) could be identified with MRM using unique peptides. Assessment of MUP content in urine, extracts, and dust samples showed good correlation between MRM and other methods working with different detection principles. All 6 identifiable MUPs were found in electrophoretically separated urine bands, but only MUP3 and MUP20 were above LOQ in unseparated mouse urine, and only MUP3, MUP4, and MUP20 were found in mouse epithelial extracts. Glycan heterogeneity was noted among 4 individual inbred mice: of 13 glycan structures detected, 8 were unique to one mouse, and only 2 glycan modifications were present in all 4 mice.

CONCLUSIONS

Using mass spectrometry and MRM, mouse allergen extracts and urine samples are shown to be complex and heterogeneous. The efficacy and safety of commercial mouse allergen extracts will be improved with better controls of allergen content.

Molecular IgE sensitization profiles of urban and rural children in South Africa

BACKGROUND

Allergens can act as disease-triggering factors in atopic dermatitis (AD) patients. The aim of the study was to elucidate the molecular IgE sensitization profile in children with and without AD living in urban and rural areas of South Africa.

METHODS

Specific IgE reactivity was assessed in 166 Black South African children aged 9-38 months using a comprehensive panel of microarrayed allergens. According to clinical characterization children fell in four groups, urban AD cases (n = 32), urban controls (non-AD, n = 40), rural cases (n = 49) and rural controls (non-AD, n = 45).

RESULTS

IgE reactivity to at least one of the allergens was detected in 94% of urban and 86% of rural AD children. House dust mite (HDM; 81% urban, 74% rural AD) and animal-derived allergens (50% urban, 31% rural AD) were the most frequently recognized respiratory allergens, whereas IgE to pollen allergens was almost absent. Urban AD children showed significantly higher frequency of IgE reactivity (50%) to mouse lipocalin, Mus m 1, than rural AD children (12%). The most frequently recognized food allergens were from egg (63% urban, 43% rural AD), peanut (31% vs 41%), and soybean (22% vs 27%), whereas milk sensitization was rare. α-gal-specific IgE almost exclusively occurred in rural children (AD: 14%, non-AD: 49%).

CONCLUSION

Molecular allergy diagnosis detects frequent IgE sensitization to HDM, animal but not pollen allergens and to egg, peanut, and soy, but not milk allergens in African AD children. Urban AD children reacted more often to Mus m 1, whereas α-gal sensitization is more common in rural children likely due to parasite exposure.

In silico analysis of a major allergen from Rattus norvegicus, Rat n 1, and cross-reactivity with domestic pets

Background: Lipocalins play a role in the cellular trafficking of pheromones and are involved in allergic responses to domestic pets. However, the cross-reactivity among allergens of this group has been poorly explored, and the pheromone linking capacity is not well characterized. The aim of this study was to explore cross-reactive epitopes and pheromone linking capacity among Rat n 1 and homologues in domestic pets through an in silico approach. Methods: ElliPro and BepiPred in silico tools were used to predict B cell linear and cross-reactive epitopes. The pheromone linking capacity was explored by docking virtual screening with 2-ethylhexanol, 2,5-dimethylpyrazine, 2-sec-butyl-4,5-dihydrothiazole, and 2-heptanone ligands. Results: According to the analysis, Rat n 1 shares 52% identity with Equ c 1, Can f 6, Fel d 4, and Mus m 1 allergens. The overlapping structures analysis  revealed high structural homology (root mean square deviation < 1). Four lineal and three discontinuous epitopes were predicted on Ra t n 1. A lineal epitope located between amino acids residues 24 and 36 was highly conserved on all allergens explored. A cross-reactive discontinuous epitope (T142, K143, D144, L145, S146, S147, D148, K152, L170, T171, T173, D174) was also found. Docking molecular simulations revealed the region involved in linking ligands, and we identified the properties of the binding of four pheromones and the binding potential of Rat n 1. Critical residues for interactions are reported in this study. Conclusions: We identified some possible allergens from Rattus norvegicus, and those allergens could have cross-reactivity with allergens from some animals. The results need to be confirmed with in vitro studies and could be utilized to contribute to immunotherapy and reduce allergic diseases related to lipocalins.