Personal exposure to house dust mite allergen in bed: nasal air sampling and reservoir allergen levels

BACKGROUND: Assessment of personal exposure to dust mite allergen has relied on proxy measures. Only recently has a means to directly measure inhaled allergen particle number become available (the intra-nasal air sampler). OBJECTIVE: To quantify inspired dust mite group 1 and group 2 allergen-bearing particles in bed in undisturbed conditions prior to sleep by nasal air sampling and to investigate the relationship between inhaled particles and reservoir allergen levels. METHODS: Twelve volunteers wore nasal samplers in bed for 6 evenings, nose-breathing in undisturbed conditions. Allergen-bearing particles ('halos') were detected by immunostaining for Der p 1, Der p 2, or Der p 1 and Der p 2 together, and counted by light microscopy. Count data were square root transformed for analysis of variance. Mattress dust samples were assayed for Der p 1 and Der p 2 concentrations. RESULTS: Square root detransformed mean particle counts per 30-min sample were: Der p 1, 4.22; Der p 2, 5.9; Der p 1 + Der p 2, 4.87; and for all samples, 5.01, with no difference between the groups. With replicate samples, halo number correlated significantly with mattress allergen concentrations (Der p 1 r = 0.80, P < 0.01; Der p 2 r = 0.68, P < 0.02). CONCLUSION: Nasal air sampling can be used to quantify nocturnal Der p exposure in undisturbed conditions in an area with moderate exposure to mite allergen and can provide a direct measure of inhaled mite allergen. The choice of either Der p 1 or Der p 2 is appropriate for this purpose.     

House dust mite allergen exposure in infancy

BACKGROUND: Infancy may be a critical time for exposure to house dust mite allergens, when exposure to high levels can increase the risk of allergic sensitization and the development of asthma in later life. OBJECTIVE: To measure house dust mite allergen (Der p 1) concentration in the infants' environment and examine lifestyle factors which may influence mite allergen exposure. METHODS: Infants aged between 4 and 12 months (n = 134) from the western region of Sydney, Australia. participated. Reservoir dust samples were collected from four sites within each home: infant's bed, second bed (adult or second child's bed), lounge floor and sheepskins (where available). Settling aeroallergen was collected for 10-14 d in Petri dishes in the infant's room. Der p 1 was measured by ELISA. A questionnaire on types of bedding, sleeping and playing patterns of the infant was completed by the parents at the time of dust collection. RESULTS: All infants were exposed to at least one site with Der p 1 concentrations greater than 10 microg/g fine dust. The mean settling aeroallergen level in the infants' room was 24 ng De p l/m2 day and this was weakly related to bed allergen levels (r=0.21, P<0.05). Mattress type had a weak effect on Der p 1 levels as measured in the whole bed (P = 0.07), while bed cover and bed type had no effect (P>0.6). The mean product of time spent at a site and its allergen concentration was highest for beds in 69% of infants. CONCLUSION: The high level of allergen exposure in the environment of this group of infants places them at an increased risk of early sensitization and development of asthma. Any strategy to reduce asthma prevalence should address these high and avoidable levels.     

Clinical benefits of treatment with SQ house dust mite sublingual tablet in house dust mite allergic rhinitis

Treatment with SQ (standardised quality) house dust mite sublingual tablet for 1 year resulted in a decreased probability of having an allergic rhinitis (AR) exacerbation day (from 11% [placebo] to 5% [SQ house dust mite sublingual tablet]) and an increased probability of having a mild AR day (from 16% [placebo] to 34% [SQ house dust mite sublingual tablet]).     

Sequence polymorphisms of the Der p 3 house dust mite allergen

Background The trypsin-like protein Der p 3 is a major allergen of Dermatophagoides pteronyssinus. Like other vertebrate and invertebrate trypsin-like molecules, isoelectricfocusing studies with the natural Der p 3 protein have indicated that several isoforms exist. Objective To determine the extent of the sequence variation of the Der p 3 allergen and distinguish at the molecular level, whether the sequence isoforms represent allelic variants or multiple genes of the allergen. Methods Five cDNA clones of Der p 3 have been isolated from a λ gt 10 D. pteronyssinus library, using a radiolabelled polymerase chain reaction (PCR) Der p 3 P3WS1 probe and sequenced. Southern blot and inverse PCR analysis of Eco RI digested genomic DNA was performed. Results Southern blot analysis of Eco RI digested genomic DNA showed that the DNA encoding Der p 3 was located on a single 3.5 kb fragment and inverse polymerase chain reaction analysis (PCR) of this DNA showed that there was only a single Der p 3 gene on this 3.5 kb fragment. The nucleotide sequence of one of the clones was identical to the original Der p 3 P3WS1 clone and two clones ditfered only in their 3′untranslated sequences. The other two contained nucleotide changes which lead to several substitutions at the amino acid level, both conservative and non conservative. Clone 3 had 98.7% identity with Der p 3 P3WS1. One clone for which the full sequence was not available (clone 4) had only 84.4% identity with the original clone and is therefore consistent with an isoallergen. Conclusions These data along with our previous genomic sequence shows that for the most part, the Der p 3 allergen has only minor sequence variations (variants) although the isoallergen indicated by clone 4 needs further investigation. It is now evident that Der p 3 is encoded by a single gene and that most cDNA clones constructed from commercial mites show only minor sequence variation similar to that observed for the group I and group 2 house dust mite allergens.     

Influence of mattress characteristics on house dust mite allergen concentration

BACKGROUND: Exposure to a high level of house dust mite allergens (HDMAs) is considered as a risk factor for HDM sensitization and development of asthma in genetically disposed people. Mattresses are one of the most important sources of HDMA in people's living environment. OBJECTIVE: The aim of this study was to evaluate the association between mattress characteristics and HDMA concentrations on mattresses. METHODS: Dust samples of mattress surfaces were taken to evaluate the level of Der p 1 allergen. All participants filled in a questionnaire about the type of mattress, the type of covering (upper layer) of the mattress, dwelling characteristics and cleaning habits. Humidity and temperature of the bedroom were measured at the time of dust sampling. RESULTS: One hundred and sixty-eight questionnaires were filled in. Synthetic upper layer of the mattress was associated with a higher level of Der p 1 compared with cotton upper layer (2.6 vs. 0.8 microg/g Der p 1). Moreover, higher relative humidity (RH) was associated with significant higher concentrations and density of Der p 1. CONCLUSIONS: Two factors were associated with lower levels of Der p 1 found on mattresses, namely: a cotton upper layer of the mattress compared with a layer of synthetic material and lower RH at the time of sampling. As far as we know, the association between type of upper layer and concentration of Der p 1 has not been described before and could lead to the formulation of practical advices in order to reduce HDMA concentrations on mattresses.     

Proteolytic,lipidergic and polysaccharide molecular recognition shape innate responses to house dust mite allergens

House dust mites (HDMs) are sources of an extensive repertoire of allergens responsible for a range of allergic conditions. Technological advances have accelerated the identification of these allergens and characterized their putative roles within HDMs. Understanding their functional bioactivities is illuminating how they interact with the immune system to cause disease and how interrelations between them are essential to maximize allergic responses. Two types of allergen bioactivity, namely proteolysis and peptidolipid/lipid binding, elicit IgE and stimulate bystander responses to unrelated allergens. Much of this influence arises from Toll-like receptor (TLR) 4 or TLR2 signalling and, in the case of protease allergens, the activation of additional pleiotropic effectors with strong disease linkage. Of related interest is the interaction of HDM allergens with common components of the house dust matrix, through either their binding to allergens or their autonomous modulation of immune receptors. Herein, we provide a contemporary view of how proteolysis, lipid-binding activity and interactions with polysaccharides and polysaccharide molecular recognition systems coordinate the principal responses which underlie allergy. The power of the catalytically competent group 1 HDM protease allergen component is demonstrated by a review of disclosures surrounding the efficacy of novel inhibitors produced by structure-based design.     

Nonlinear relations between house dust mite allergen levels and mite sensitization in farm and nonfarm children

BACKGROUND: Low sensitization rates to common allergens have been observed in farm children, which might be due to high exposure to microbial agents. It is not known how microbial agents modify the association between specific allergen exposure and sensitization. OBJECTIVE: To examine the relations between house dust mite allergen exposure and mite sensitization in farm and nonfarm children and to assess the effects of microbial agents levels on this association. METHODS: Major mite allergens of Dermatophagoides pteronyssinus (Der p 1) and Dermatophagoides farinae (Der f 1), endotoxin, beta(1,3)-glucans and fungal extracellular polysaccharides were measured in mattress dust of 402 children participating in a cross-sectional study in five European countries. Mite allergen (Der p 1 + Der f 1) levels were divided into tertiles with cut-offs 1.4 and 10.4 microg/g. Sensitization was assessed by measurement of allergen-specific immunoglobulin E against house dust mite. RESULTS: Prevalence ratios of mite sensitization for medium and high when compared with low mite allergen levels were 3.1 [1.7-5.7] and 1.4 [0.7-2.8] respectively. Highest mite sensitization rates at intermediate exposure levels were consistently observed across country (except for Sweden) and in both farm and nonfarm children. The shape of the dose-response curve was similar for above and below median mattress microbial agent levels, but the 'sensitization peak' appeared to be lower for above median levels. CONCLUSIONS: Our data suggest a bell-shaped dose-response relationship between mite allergen exposure and sensitization to mite allergens. In populations with high microbial agent levels and low sensitization rates, the curve is shifted down.     

哮喘患儿家庭内尘螨过敏原分布特征及其临床意义

目的了解北京地区尘螨过敏性哮喘患儿家庭环境内尘螨过敏原含量分布特征,初步探讨尘螨过敏原暴露水平的临床意义。方法选取54例尘螨过敏性哮喘患儿,其中男性37例,女性17例;年龄3～16岁,平均年龄8岁2个月。采集患儿家庭中床垫、枕头、卧室地板、客厅地板及沙发的灰尘,采用酶联免疫吸附分析（ELISA）测定以上灰尘样本中户尘螨1组过敏原（Der p1）和粉尘螨1组过敏原（Der f1）的含量;应用荧光ELISA测定患儿血清尘螨特异性IgE浓度;评估患儿哮喘临床控制情况,应用化学发光法测定患儿呼出气一氧化氮浓度（FeNO）。结果采集灰尘样本255份,以中位数（最小值～最大值）表示尘螨过敏原含量,床垫、枕头和沙发灰尘样本中Derf1和Derp1的含量显著高于卧室地板和客厅地板灰尘样本中尘螨过敏原含量。Derf1平均含量为0.13μg/g,显著高于Derp1平均含量0.02μg/g（P〈0.05）。Derp1和Derf1联合暴露的最高含量平均为2.18（0.07～54.59）μg/g。Der p1和Der f1联合最高暴露含量≥10.00μg/g、2.00～10.00μg/g、0.05～2.00μg/g的例数分别为4例（7.4%）、24例（44.4%）、26例（48.1%）。其中未控制组患儿家庭内尘螨过敏原最高暴露水平为27.41（0.23～54.59）μg/g,均显著高于部分控制组和控制组哮喘患儿尘螨过敏原最高暴露水平1.66（0.07～26.27）μg/g、2.90（0.37～33.75）μg/g（P〈0.05）。不同sIgE浓度分级组间尘螨过敏原最高暴露水平的差异、不同FeNO浓度范围组间尘螨过敏原最高暴露水平差异均无统计学意义。结论北京地区尘螨过敏性哮喘患儿家庭尘螨以Der f1为主,床垫、枕头及沙发灰尘样本是Der p1和Der f1的主要来源;哮喘未控制者的尘螨过敏原最高暴露水平明显增高。     

Silverfish protein in house dust in relation to mite and total arthropod level

Two assays have been developed to measure arthropod levels in house dust. The first assay measures silverfish antigens. The second assay measures invertebrate tropo-myosin and gives a global assessment of the level of atthropod-derived material. These assays and a Der p 1 and Der p 2 assay were used to analyse 53 dust samples. In most dust samples the ratio of tropomyosin/Der p 2 was higher than in mite body extract, indicating that the assay measures other arthropods besides mites. Silverfish antigen was detectable in most of the dust samples. In many homes in which the inhabitants were unaware of the presence of silverfish, silverfish antigen was detectable. Therefore for information on exposure an immunochemical analysis is superior to a questionnaire.     

Distribution of house dust mite allergen: comparing house dust mite allergen levels in dust samples collected from different sites on living room floors with smooth coverings

BACKGROUND: The distribution of house dust mite allergen (Der p1) in living rooms with smooth floor coverings, as measured in the middle compared with the border of the floor was investigated. It was hypothesized that activity causes displacement of Der p1, from the middle towards the border. METHODS: Dust samples from the middle and border of 50 floors with smooth coverings were collected and analysed on Der p1 content in a standardized way. RESULTS: The Der p1 exposure expressed as per unit area (ng/m2) showed that border samples contained significantly more Der p1 compared with middle samples (median: 2.57 vs 0.27, respectively, P = 0.023). Presence of pets and presence of more than two inhabitants increased the difference. When expressed as per unit weight of dust (ng/g), significant differences were only detected when comparing Der p1 content of samples collected in households with three or more inhabitants [median: 2 (border) vs 53 (middle), respectively; P = 0.035]. CONCLUSIONS: The Der p1 is unequally distributed on living room floors with smooth coverings, most likely because of displacement of dust from the middle towards the border due to activity. Expression as ng/g of dust and ng/m2 could not obviously be interchangeable.     

Molecular characterization of Der p 10: a diagnostic marker for broad sensitization in house dust mite allergy

Background Tropomyosins represent clinically relevant seafood allergens but the role of mite tropomyosin, Der p 10, in house dust mite (HDM) allergy has not been studied in detail. Objective To express and purify a recombinant Der p 10 with equivalent IgE reactivity as natural Der p 10 and to evaluate its IgE reactivity and allergenic activity in HDM‐allergic patients. Methods rDer p 10 was expressed in Escherichia coli, purified and characterized by mass spectrometry and circular dichroism. It was tested for IgE reactivity in 1322 HDM‐allergic patients. Detailed IgE‐reactivity profiles to six HDM allergens (Der p 1, 2, 5, 7, 10, 21) were established for subgroups of Der p 10‐positive and ‐negative patients. The allergenic activity of rDer p 10 was evaluated in basophil degranulation experiments. Results rDer p 10 is an α‐helical protein sharing IgE epitopes with nDer p 10. It is recognized by 15.2% of HDM‐allergic patients. Der p 10‐negative patients were primarily sensitized to Der p 1 and/or Der p 2, whereas Der p 10‐positive patients reacted to several other HDM allergens besides the major allergens (Der p 1, Der p 2) or showed a rather selective Der p 10 reactivity. The allergenic activity of Der p 10 was generally low but patients could be identified who suffered from clinically relevant HDM allergy due to Der p 10 sensitization. Conclusion and Clinical Relevance Der p 10 may be a diagnostic marker for HDM‐allergic patients with additional sensitization to allergens other than Der p 1 and Der p 2. Such patients may require attention when allergen‐specific immunotherapy is considered. Cite this as: Y. Resch, M. Weghofer, S. Seiberler, F. Horak, S. Scheiblhofer, B. Linhart, I. Swoboda, W. R. Thomas, J. Thalhamer, R. Valenta and S. Vrtala, Clinical & Experimental Allergy, 2011 (41) 1468–1477.     

Effect of improved home ventilation on asthma control and house dust mite allergen levels

Background:  The warm, humid environment in modern homes favours the dust mite population, but the effect of improved home ventilation on asthma control has not been established. We tested the hypothesis that a domestic mechanical heat recovery ventilation system (MHRV), in addition to allergen avoidance measures, can improve asthma control by attenuating re-colonization rates.
Methods:  We conducted a randomized double-blind placebo-controlled parallel group trial of the installation of MHRV activated in half the homes of 120 adults with asthma, allergic to Dermatophagoides pteronyssinus . All homes had carpets steam cleaned and new bedding and mattress covers at baseline. The primary outcome was morning peak expiratory flow (PEF) at 12 months.
Results:  At 12 months, the primary end-point; change in mean morning PEF as compared with baseline, did not differ between the MHRV group and the control group (mean difference 13.5 l/min, 95% CI: −2.6 to 29.8, P  = 0.10). However, a secondary end-point; evening mean PEF, was significantly improved in the MHRV group (mean difference 24.5 l/min, 95% CI: 8.9–40.1, P  = 0.002). Indoor relative humidity was reduced in MHRV homes, but there was no difference between the groups in Der p 1 levels, compared with baseline.
Conclusions:  The addition of MHRV to house dust mite eradication strategies did not achieve a reduction in mite allergen levels, but did improve evening PEF.     

Molecular cloning and immunological characterization of the house dust mite allergen Der f 7

Background The allergen Der p 7 from Dermatophagoides pteronyssinus has been defined by molecular cloning and shown to be an important specificity in 50% of miteallergic patients. Objective This study compares the cDNA sequence and serological reactivity of Der f 7 from D. farinae with Der p 7. Method cDNA encoding Der f 7 was amplified by polymerase chain reaction. sequenced and expressed as a fusion with glutathione-S-transferase for IgE and monoclonal antibody binding studies. Results Der f 7 cDNA encoded a 213 polypeptide containing a predicted 17 amino acid leader sequence, no cysteines and a single N-glycosylation site similar to Der p 7. The predicted 196 residue mature polypeptide had 86% identity lo Der p 7 and a calculated molecular weight of 22 34SDa. No homologues were found in searches of the data banks. The Der f 7 fusion protein showed a single band of 46 k Da by sodium dodccyl snlfute-polyaerylamide gel electrophoresis (SDS-PAGF) and reacted with IgE antibodies in 19/41 (46%) of sera from asthmatic children. The degree of binding was usually 30% of that to Der p 7 consistent with the exposure of the patients to D. Pteronyssinus. Monoclonal antibodies (WH9 and WH22) against Der p 7 reacted with Der f 7 but inhibition studies showed a 10-fold difference in reactivity. Conclusion Der f 7 has a predicted 213 residue polypeptide with 86% homology and serological cross reactivity to Der p 7.