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.     

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.     

Determinants of house dust mite allergen in homes in Wellington, New Zealand

Objectives To measure levels of the major Dermatophagoides pteronyssinus allergen (Der p 1) in homes in Wellington, New Zealand, and to examine factors which affect these levels. Methods As part of a study of risk factors for asthma among 474 8–10-year-old children, standard procedures were used to collect reservoir dust and to measure Der p 1 levels on the living room floor and child's bedroom floor and bedding. Der p 1 levels were analysed both as geometric mean μg/g of fine dust and as μg/m². Questionnaires collected information about factors which might influence these levels, and an average relative humidity in the bed and on the bedroom floor was also measured. Results Similar geometric mean levels of Der p 1 were found at each floor site – 25.5μg/g (95% CI: 22.8–28.5) in the living room and 26.4 μg/g (95% CI: 23.7–29.3) on the child's bedroom floor. The geometric mean level of Der p 1 in the child's bed was 46.6 μg/g (95% CI: 42.3–51.3). After controlling for possible confounders, geometric mean living room and bedroom floor Der p 1 levels were significantly higher in households with older carpet than households with no carpets or newer carpets, and higher in the autumn. Households with three or more children had higher levels of Der p 1 than households with fewer children. Bedding levels were significantly higher in beds with kapok or inner sprung mattresses, or wool underlays and at relative humidities above the mean (51%). Conclusion The very high levels of house dust mite allergen (Der p 1) found in Wellington are likely to be due to a variety of life-style and climatic factors. However, the type and age of floor covering appears to be the single most important factor.     

Predictors of high house dust mite allergen concentrations in residential homes in Sydney

BACKGROUND: In parts of coastal Australia, house dust mite allergen concentrations in homes are often very high with at least 80% of homes in Sydney exceeding concentrations of 10 microg of allergen per gram of fine dust. In this study, we report the relation between characteristics of the home environment and house dust mite allergen concentrations at three sites in Sydney homes. METHODS: A total of 616 families were recruited as part of the Childhood Asthma Prevention Study (CAPS). Information about the home environment and structural aspects of the home was collected using a questionnaire. Samples of dust were collected from the parents' bed, the bedroom floor and the living room floor and assayed for Der p 1. RESULTS: A total of 68% of participants' beds, 65% of bedroom floors and 56% of living room floors had Der p 1 concentrations above 10 microg/g, with the highest concentrations of allergen in the bed. The most significant predictor of high Der p 1 concentrations in the bed and floors was the age of the home. We also found that beds with mattresses over two years old and with woollen or synthetic blankets or synthetic quilts had higher Der p 1 concentrations. Carpeted floors had higher Der p 1 concentrations than hard floors. CONCLUSION: The finding that high Der p 1 allergen concentrations in homes with carpets and older mattresses indicates that control strategies directed at these sources are likely to be effective in reducing exposure. Alternatives such as the use of house dust mite impermeable mattress encasings on older mattresses may also be effective in reducing exposure.     

Cytokine responses to Der p 1 and Der p 7: house dust mite allergens with different IgE-binding activities

BACKGROUND: There is very limited information comparing T-cell responses to different house dust mite (HDM) allergens even though T cells are essential in the initiation and regulation of immunoglobulin (Ig) E synthesis and eosinophilia. OBJECTIVE: To compare the level of T-cell proliferation and cytokine production to the group 1 and group 7 HDM allergens which are known to have different IgE-binding capabilities. METHODS: Freshly isolated peripheral blood mononuclear cells (PBMC) from HDM-allergic and HDM-nonallergic donors were stimulated with the group 1 and group 7 allergens of Dermatophagoides pteronyssinus and the level of proliferation as well as IL-5 and IFNgamma production were measured. RESULTS: The proliferative and IL-5 production to the group 1 and group 7 allergens were equivalent despite the group 7 allergen's lower frequency of IgE-binding. However more IFNgamma was produced to Der p 7 than to Der p 1, particularly for the nonallergic donors. As expected IL-5 production was much higher for PBMC from the allergic donors than for cells from nonallergics; however, there was no difference in the level of T-cell proliferation between the donor groups. CONCLUSION: The relative importance of the individual HDM allergens is normally determined by measuring the frequency of IgE-binding to the allergen in sera from an allergic population. The equivalent increased IL-5 response of PBMC from allergic people to the group 1 and group 7 allergens despite the different IgE-inducing activity indicates that these allergens may be equally capable of contributing to an asthmatic response by inducing eosinophilia.     

Seasonal trends in house dust mite allergen in children's beds over a 7-year period

BACKGROUND: House dust mite (HDM) allergy is closely linked to the expression of asthma and other allergic diseases. Understanding factors influencing variation in allergen may help in controlling allergic disease. The objective of this study was to investigate the effects of seasonal changes in climate, type of bed used in very early childhood and anti-mite interventions on HDM allergen concentration. METHODS: Participants were enrolled in a randomized-controlled trial of HDM avoidance. Der p 1 was measured in dust samples from children's beds on 13 occasions, from birth to age 5 years, between 1997 and 2004. Bed types were categorized as bassinette, cot or bed. The effects of study month, type of bed and intervention group on HDM allergen concentration were estimated by multiple linear regression. The relation between climatic variables and HDM allergen concentration was investigated using a polynomial distributed lag model. RESULTS: House dust mite allergen concentrations were initially low in cots and bassinettes in 1997/1998, peaked in bassinettes and beds between 1999 and 2001 and then slowly declined during the period 2002/2004. Seasonal fluctuations occurred with minima in summer and two- to threefold higher maxima during late autumn. Allergen peaks were correlated with relative humidity peaks 2 months previously. Seasonal changes in allergen were not affected by the HDM avoidance intervention. CONCLUSIONS: House dust mite allergen concentrations in Sydney beds fluctuate approximately two- to threefold on an annual cycle, partly determined by relative humidity, with peaks in late autumn and minima in summer. Fluctuations of this magnitude might be sufficient to influence asthma symptoms.     

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.     

Genetic polymorphisms of major house dust mite allergens

BACKGROUND: Polymorphic sequence substitutions in the major mite allergens can markedly affect immunoglobulin E binding and T cell responses, but there are few studies on environmental isolates from Dermatophagoides pteronyssinus and none for D. farinae. OBJECTIVE: To determine the sequence variation of the group 1 and 2 allergens from environmental D. pteronyssinus and D. farinae. METHODS: RNA from each species was isolated from homes in Bangkok and the sequence of Der p 1, Der p 2, Der f 1, and Der f 2 determined from cDNA produced by high fidelity polymerase chain reactions. RESULTS: The enlarged data set revealed preferred amino acid substitutions in residues 19, 81, and 215 of Der p 1 as well as sporadic changes. Der p 2 showed frequent variations with clusters of amino acid substitutions, but the canonical Der p 2.0101 was not found in any of 17 sequences. Der f 2 showed variants with clusters of substitutions similar to Der p 2 but in different amino acid positions and without any structural concordance. Der f 1 in contrast to the other allergens had few amino acid sequence substitutions. CONCLUSIONS: The sequence information on variants provides data important for the optimal design of allergen formulations and useful for the genetic engineering and structure-function analyses of the major allergens.     

Heterogeneous proteolytic specificity and activity of the house dust mite proteinase allergen Der p I

Background Exposure of the skin or respiratory tract to proteinases is frequently associated with allergic sensitization. This is of particular significance in the domestic indoor environment where the proteolytic activity of Der p I, the group I allergen of the house dust mite Dermatophagoides pteronyssinus, may influence the allergenicity of mites. Using class-specific proteinase inhibitors and active-site affinity chromatography, we have previously shown that Der p I exhibits a mixed cysteine-serine proteinase activity. Measurement of the amount of cleavage, however, did not determine whether the inhibitors used were targeting exactly the same proteolytic mechanism. Objective To resolve this issue, we have examined whether the cleavage specificity of the cysteine and serine proteinase activities of Der p I was the same. Methods HPLC and mass spectrometry were used to analyse and identify the products of a Der p I-digested peptide substrate and thus identify the peptide bonds cleaved. Results Der p I cleaves different peptide bonds, depending upon the class of proteolytic mechanism used. In the model peptide substrate insulin B chain, the cysteine and serine proteinase activities of Der p I showed preference for glutamic acid and arginine respectively in the P1 position. Conclusion These data suggest the existence of more than one mechanistic form of the allergen immunologically identified as Der p I. If proteolytic activity is indeed a function of allergenicity, this information may have important implications for the pathogenicity of Der p I and the ability of innate antiproteinase defences in the respiratory tract to prevent immune sensitization.     

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.     

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.     

Cord blood mononuclear cell cytokine responses in relation to maternal house dust mite allergen exposure

BACKGROUND: Cord blood mononuclear cells have demonstrated specific immune responses to environmental allergens. OBJECTIVE: To establish whether the nature of this response is related to the level of maternal antenatal exposure to house dust mite (HDM) allergen and, hence, whether antenatal allergen avoidance may have a role in the prevention of allergic sensitization in children. METHODS: Children with a family history of asthma were recruited antenatally as subjects in a randomised controlled trial: the Childhood Asthma Prevention Study. HDM allergen (Der p 1) concentrations were measured in dust collected from the maternal bed at 36 weeks gestation. Cord blood mononuclear cells were stimulated in culture, separately, with phytohaemaglutinin (PHA) and HDM extract. Cytokine IL-4, IL-5, IL-10 and IFN-gamma concentrations in supernatant were measured by ELISA. mRNA signals for these cytokines were measured using RT-PCR. RESULTS: The median concentration of HDM allergen was 18.4 microg/g (interquartile range 7.3-35.3 microg/g). Median concentrations of IL-4, IL-5, IL-10 and IFN-gamma, after PHA stimulation were 4, 19, 401 and 1781 pg/mL, respectively. After HDM allergen stimulation the median concentrations were 0, 0, 20 and 14 pg/mL, respectively. The distribution of mRNA cytokine signals was similar. Neither cytokine protein concentrations nor cytokine mRNA signal levels were correlated with the concentration of HDM allergen in the mothers' beds at 36 weeks gestation. CONCLUSION: These findings do not support the view that the prevention of allergic disease in children requires the institution of HDM avoidance interventions during pregnancy.     

Quantitative structural and biochemical analyses of tight junction dynamics following exposure of epithelial cells to house dust mite allergen Der p 1

BACKGROUND: House dust mite allergen Der p 1 is a cysteine peptidase. Previously, we have suggested that the proteolytic activity of this allergen may contribute to asthma by damaging the barrier formed by the airways epithelium. OBJECTIVE: The present study applied novel techniques to compare changes in permeability with quantitative events in tight junctions (TJs) and desmosomes (DMs) of epithelial cells exposed to Der p 1. METHODS: Confluent monolayers of Madin-Darby canine kidney (MDCK) and 16HBE14o-human bronchial epithelial cells were used as experimental models. Permeability was estimated from mannitol clearance. Digital imaging with quantification of TJs and DMs was achieved by fluorescent antibody staining and 2-photon molecular excitation microscopy (2PMEM). Biochemical changes in TJs were studied by immunoblotting, radiolabelling and immunoprecipitation. RESULTS: Der p 1 caused a time-dependent breakage of TJs and reduction in their content of the protein ZO-1. Reduction in ZO-1 immunofluorescence at TJs occurred with a small increase in the amount of diffuse, cytoplasmic immunoreactive ZO-1 staining. Morpho-logical changes in TJs occurred in synchrony with increases in epithelial permeability. DM puncta increased both in size and intensity of staining. Immunoblotting demonstrated that the disruption of TJ morphology was associated with cleavage of ZO-1 and occludin. Cells recovered from allergen exposure by de novo synthesis of occludin. CONCLUSION: Der p 1 could contribute to sensitization and allergic responses by degrading the function of the airway epithelial barrier.     

Inhaled formaldehyde exposure: effect on bronchial response to mite allergen in sensitized asthma patients

BACKGROUND: Formaldehyde, an indoor air pollutant, is known to be an irritant and an etiologic factor in occupational asthma. An epidemiologic study suggests that it may also increase the risk of childhood asthma for concentrations above 60 microg/m(3). AIM: To evaluate the influence of pre-exposure to low-dose formaldehyde (100 microg/m(3) in 30 min according to the World Health Organization's recommended maximum value for indoor environments) on bronchial response to Dermatophagoides pteronyssinus. METHOD: Nineteen asthmatic subjects were included. Each subject underwent a mite allergen bronchial challenge test immediately after a standardized exposure in a chamber to formaldehyde or air (random order). Induced sputum were collected 24 h before and after mite challenge. RESULTS: After formaldehyde inhalation, patients developed an immediate bronchial response at a significantly lower dose of mite allergen than after air exposure (the geometric mean PD(20) for Der p 1 was 34.3 ng after formaldehyde and 45.4 ng after placebo, P = 0.05). The late-phase reaction, expressed as the maximum fall in forced expiratory volume in 1 s (FEV(1)) from baseline, was significantly higher after formaldehyde (15%vs 11%, P = 0.046). CONCLUSION: Our study demonstrated that exposure to low levels of formaldehyde significantly enhanced bronchial responsiveness to mite allergen in mite-sensitized subjects with asthma.     

The non-proteolytic house dust mite allergen Der p 2 induce NF-κB and MAPK dependent activation of bronchial epithelial cells

Background House dust mites (HDM) are well‐known as a source of indoor aeroallergens and for causing allergic airway diseases. Some proteolytic HDM allergens are known to activate respiratory epithelial cells to produce pro‐inflammatory mediators, while there is limited knowledge regarding such activity among non‐proteolytic HDM allergens. Objective To investigate whether Der p 2, a major non‐proteolytic allergen of Dermatophagoides pteronyssinus, activates respiratory epithelial cells to produce mediators involved in asthma pathogenesis and to elucidate the mechanism of such activation. Methods The human bronchial epithelial cell line BEAS‐2B, normal human bronchial epithelial (NHBE) cells and the alveolar epithelial cell line A549 were exposed to recombinant Der p 2. Following exposure, we analysed a panel of soluble mediators and cell adhesion receptors involved in asthma pathogenesis by promoting recruitment, survival and binding of inflammatory cells. The involvement of nuclear factor (NF)‐κB and mitogen‐activated protein kinases (MAPKs) was studied using specific inhibitors. Results Der p 2 activated bronchial BEAS‐2B and NHBE cells, but not alveolar A549 cells. In BEAS‐2B cells Der p 2 induced dose‐dependent up‐regulation in both mRNA level and protein secretion of granulocyte‐macrophage colony‐stimulating factor, IL‐6, IL‐8, monocyte‐chemotactic protein‐1 and macrophage inflammatory protein‐3α. Secretion as well as surface expression of intercellular adhesion molecule (ICAM)‐1 was also up‐regulated, which was associated with increased adhesion of monocytes to the epithelial cells. The release of cytokines and chemokines was regulated by NF‐κB and MAPK activation in different ways, while expression of ICAM‐1 was solely dependent on NF‐κB activation. Conclusion These results show that Der p 2 activates respiratory epithelial cells, indicating that this non‐proteolytic allergen, in addition to its immunogenic properties, can aggravate respiratory airway disease by adjuvant‐like activation of the lung epithelium.     

Molecular mimicry as the key to the dominance of the house dust mite allergen Der p 2

Evaluation of: Trompette A, Divanovic S, Visintin A et al. Allergenicity resulting from functional mimicry of a Toll-like receptor complex protein. Nature 457, 585–588 (2009).

The majority of complex sources of allergen contain a small number of dominant allergens that bind at least half of the IgE antibodies of allergic subjects. For the house dust mite Dermatophagoides pteronyssinus, these allergens are Der p 1 and Der p 2. There is evidence that the cysteine-protease activity of Der p 1 imparts adjuvant activity to the allergen. It has now been shown that Der p 2 mimics the activity of its fellow ML-domain protein, MD-2, by presenting lipopolysaccharide to Toll-like receptor-4 for the activation of inflammatory genes. In accord with this, Der p 2 presented with lipopolysaccharide also induced enhanced type 1 allergic sensitization of mice, even when they were deficient in MD-2. The mimicry of MD-2 can thus also self adjuvant Der p 2 to enhance it allergenicity. This not only describes an intriguing mechanism for enhancing allergenicity but also, since both of the dominant mite allergens have intrinsic adjuvant activity, exemplifies an important principle for driving allergic sensitization.     

Hyposensitization in asthmatics with mPEG modified and unmodified house dust mite extract

Forty-six asthmatics with verified allergy to the house dust mite, D. pteronyssinus (Dp), participated in a double-blind study comparing the effect of 2 years' hyposensitization with two different Dp extracts. Two groups received either monomethoxypolyethylene glycol modified (mPEG) Dp extract or the corresponding non-modified extract, and a third group acted as controls receiving no injections. Medicine consumption, symptom scores, and peak expiratory flow (PEF) were recorded daily from September to December prior to and after 6 and 18 months of treatment. Changes were calculated choosing changes greater than or equal to 10% as relevant. In addition, patients were asked to give their direct assessment of the clinical effect at the end of the study. After 6 months, there was an improvement in symptoms + medication in 11/14 of Dp-treated, 6/17 of the mPEG-Dp group (P greater than 0.05) and 3/15 of openly treated controls. Few patients had changed in PEF. During the second year, several Dp-treated relapsed and some controls improved. At the end of the study the same improvement rate was seen in all groups. Similarly, the retrospective questionnaire data did not disclose any significant differences between groups after 2 years. In conclusion, hyposensitization with unmodified Dp extract seemed to have a favourable short-term effect on bronchial symptoms + medication in the majority of patients. When mainly on maintenance dose, the beneficial effect was reduced. The mPEG modification of the extract had reduced not only allergenicity but also the clinical effect of equal doses. Changes in medicine and symptom scores only partly correlated to retrospective assessment, thus stressing the problems in this kind of evaluation.     

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。     

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.     

House dust mite allergen (Der p 1) accumulation on new synthetic and feather pillows

BACKGROUND: We have previously demonstrated that synthetic pillows contain significantly more Der p 1 than feather pillows. The aim of this study was to compare the accumulation of Der p 1 allergen on new synthetic and new feather pillows. METHODS: Der p 1 was measured in dust samples from pairs of synthetic and feather pillows placed together on 12 beds over a 12-month period. RESULTS: After 12 months synthetic pillows contained higher concentrations of Der p 1 (19.28 microg/g; 95% confidence interval: 9.76-38.07) than feather pillows (6.45 microg/g; 2.96-14.05). There was a significant correlation between Der p 1 concentrations of pillows at 12 months and Der p 1 concentrations of the mattresses at the beginning of the study (r = 0.72; P = 0.008 for both types of pillows). CONCLUSIONS: Synthetic pillows accumulate Der p 1 more rapidly than feather pillows and the accumulation rate of Der p 1 on pillows is governed by the Der p 1 concentration in the immediate environment they are placed in.