Guanine content and Dermatophagoides pteronyssinus allergens in house dust samples

Contribution of cysteine and serine proteases to proteolytic digestion in an allergy-eliciting house dust mite

The digestive physiology of house dust mites (HDM) is of interest to understand their allergenicity towards humans since many of their allergens are digestive enzymes and/or are excreted into airborne fecal pellets. The aim of this study is to provide insight on the biochemical basis of proteolytic digestion in Dermatophagoides pteronyssinus, the most widespread HDM species. First, assays using non-specific protein substrates on purified fecal and body extracts determined that body-associated activity is almost exclusively dependent on cysteine proteases, and specifically on major allergen Der p 1. By contrast, cysteine and serine proteases contributed similarly to the activity estimated on fecal extracts. Second, the screening of group-specific peptide-based protease inhibitors followed by ingestion bioassays revealed that the human skin-derived cysteine protease inhibitor cystatin A produces a significant reduction in mite feeding (i.e. excreted guanine), and triggers the overproduction of Der p 1 (3-fold increase by ELISA). Noteworthy, the inhibition of cysteine proteases by cystatin A also resulted in a reduction in three non-target serine protease activities. Further incubation of these extracts with exogenous Der p 1, but not with other commercial cysteine proteases, restored trypsin (Der p 3) and chymotrypsin (Der p 6) activities, indicating that Der p 1 is responsible for their activation in vivo. Finally, the role of serine proteases on the mite's digestive physiology is discussed based on their remarkable activity in fecal extracts and the autocoprophagic behavior reported in mites in this study.

Sensitisation to mites in laboratory animal workers with rhinitis

AIMS

To determine the frequency of sensitisation to mites among rhinitic laboratory animal workers and to clarify whether sensitisation could be occupational.

METHODS

Skin prick tests (SPT) were performed in 40 subjects who were working with laboratory animals in Kuopio University research units and who had been referred to Kuopio University Hospital for work related rhinitis. The SPT panel consisted of three storage mites, two house dust mites, 11 other common environmental airborne allergens, latex, and 2-4 individually relevant laboratory animals. To determine signs of mites in animal facilities, guanine was determined in 22 dust samples taken from feedstuffs or bedding material used for laboratory animals and from rooms where these materials were stored and handled.

RESULTS

Positive SPT results were found in 35 out of 40 workers: in 14 for storage mites, four for house dust mites, 25 for other common aeroallergens, as well as positive reactions to laboratory animals in 19 individuals. The guanine test was positive, indicating the presence of mite derived material in 21 out of 22 dust samples.

CONCLUSIONS

This study suggests that subjects who are occupationally exposed to laboratory animals are also exposed to mite derived allergens. Sensitisation to mites is common and may be work related.

House-dust mites and mattresses

BACKGROUND

Despite considerable efforts to develop anti dust mite strategies, surprisingly few studies have evaluated the allergen content in different types of mattresses in everyday use. This study investigated the presence of mite feces (an indicator of mite allergens) in foam and spring mattresses.

METHODS

The homes of 152 schoolchildren in Northern Norway were investigated. Dust samples were collected in a standardized way from 24 foam mattresses without covers, 68 foam mattresses with covers, and 24 spring mattresses, and the presence of mite feces detected by a guanine colorimetric paper test (Acarex).

RESULTS

We found mite feces in 15 (40.5%) of the dust samples from the foam mattresses without covers and 18 (26.3%) of the foam mattresses with covers. Only three (12.5%) of the spring mattresses contained detectable amounts of feces. Signs of dampness, age of mattress, cleaning of mattress, frequency of vacuuming the bedroom, mechanical ventilation, bedroom temperature and bedroom relative humidity were associated with the presence of mite feces. After adjustment for relevant confounders, the risk of finding mite feces was four times higher in foam compared to spring mattresses (odds ratio 4.0, 95% confidence interval (CI) 1.1-15.1), and eight times higher for the foam mattresses without cover (OR 8.1, 95% CI 1.8-36.9).

CONCLUSION

A simple replacement of foam mattresses with spring mattresses may reduce the exposure to house-dust-mite allergens.

Influence in the quality of life of the respiratory patients by environmental control and the acaricide Frontac®

The present prospective, open, observational study assessed the effect of the use of standard environmental control measures together with the application of an acaricide-containing aerosol of esbiol/benzyl benzoate/piperonyl butoxide/2-phenylphenol (Frontac) on several clinical and environmental parameters in patients suffering from perennial allergic rhinoconjunctivitis related to house dust mites (HDM). Fifty-five patients were enrolled and studied for one year. Both symptoms and the patients' quality of life (evaluated by the Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ)) were assessed at several clinic visits. The amount of HDM antigen was semi-quantitatively estimated using the guanine test. We found a significant decrease (p < 0.001) in most nasal symptoms scores: sneezing, runny nose, stuffy nose and itching. The overall quality of life (QoL) score also showed a significant improvement during the study period; the mean score decrease found was 0.86 (CI 95 %, 0.54-1.17) (p < 0.001). Five of the seven domains included in the questionnaire decreased significantly: non-hayfever symptoms; practical problems; nasal symptoms; eye symptoms, and emotions. These QoL score decreases were found during the first 3 months and later remained stable at lower levels than at baseline. The content of guanine in dust samples decreased significantly from 2.17 0.75 to 1.43 0.68 (p < 0.001). No toxic adverse events were recorded. In conclusion, these results show an improvement in the quality of life and a clinical benefit of the long-term use of the new chemical acaricide tested, together with environmental measures, in the home of patients suffering from allergic respiratory pathology.

Guanine, mite, and cockroach allergens in Costa Rican homes

Previous studies of schoolchildren in Costa Rica have shown an asthma prevalence of 23% and a high level of sensitization, particularly to mite allergens. As a continuation of these studies, some 400 dust samples were collected from various places in Costa Rica, and parts of these were analyzed for specific mite and cockroach allergens, as well as for the number of mites and amount of guanine. Guanine was quantified by a diazo, as well as an HPLC method, which were found to be highly correlated. The concentrations of guanine by the diazo method, Der p 1, Der f 1, and the number of mites were higher in bed dust than in bedroom floor dust, and it was possible to quantify mite allergens and guanine in almost all bed-dust samples. The mean levels were 2-3 times higher than the proposed risk level for elicitation of symptoms in mite-sensitive asthmatics. Bed and bedroom floor dust contained more guanine and mite allergen in humid (> 2000 mm rain) than in drier places (P < 0.05), but the number of mites in bed and bedroom floor dust was higher in less humid places (P = 0.01). The guanine content in bedroom floor dust was higher in areas with a temperate climate than in areas with a warmer climate (P < 0.001, Bartlett's chi square [BCS]), as was the number of mites (P < 0.01, Kruskal-Wallis [KW], 0.04, BCS) and the Der p 1 concentration (P = 0.01, BCS; P = 0.02, KW). The Der f 1 concentration in bedroom floor dust was higher in a warmer than in a temperate climate (P < 0.001, BCS). More guanine and mites were found in urban than in rural bed dust (P = 0.03, KW). Dust samples from the metropolitan area (temperate climate) of Costa Rica contained higher levels of guanine (P < 0.01) and Der p 1 (P = 0.07) than the coastal areas, but very little Der f 1. In these samples, guanine and Der p 1 allergen were closely related, and 2 micrograms of the allergen was equivalent to 0.49 mg of guanine. Two-thirds of bed and floor samples collected on cotton filters contained Bla g 2 allergen at mean levels of 1.6 and 2.1 units/g dust, respectively. Cockroach allergen was, however, absent in all bed samples from the metropolitan area, but did occur in very high concentrations in the coastal bed dust samples collected with tighter polyester filters. In conclusion, the concentration of guanine and Der p 1 was very high in the bed dust of Costa Rican homes. Some factors, such as humidity, small houses for large families, and type of bedding, probably favored the heavy mite infestation, which is probably related to the widespread occurrence of bronchial asthma in this country.

Benzyl-benzoate foam: effects on mite allergens in mattress, serum and nasal secretory IgE to Dermatophagoides pteronyssinus, and bronchial hyperreactivity in children with allergic asthma

Home mattresses of 24 asthmatic children with house dust mite allergy were sprayed with either benzyl-benzoate foam or placebo in a double blind fashion, 10 days before the children left the residential house for asthmatic children Istituto Pio XII (located in the Italian Alps in an environment free of mites) and went back to their own home for the Christmas and Easter holidays. A further group of 8 children, whose mattresses received no treatment, was kept as an absolute control. Two days after spraying, benzyl-benzoate or placebo were vacuumed from the mattresses. Acarex test was performed immediately before spraying and at the end of each holiday period of 20 and 10 days, respectively. Bronchial hyperreactivity as well as serum and nasal secretory specific IgE for Dermatophagoides pteronyssinus were assessed in all children immediately before leaving and within 48 hr after returning to the residential house. The results of the study show that sprayed benzyl-benzoate foam was no more effective than placebo in reducing the level of house dust mite recovered from patients' mattresses, or in reducing bronchial hyperreactivity and IgE concentration in serum and nasal secretions.

Prediction of mite allergen levels by guanine measurements in house-dust samples

We studied the sensitivity and specificity of guanine environmental tests in the evaluation of the two mite allergen levels, i.e. 2 micrograms/g and 10 micrograms/g of Der p I and Der f I, considered to be risk factors for sensitization or for the development of acute asthma. We examined 239 house-dust samples for Der p I and Der f I levels (ELISA) and guanine contents (semiquantitative guanine test and quantitative assays). All house-dust samples with class 2 or 3 guanine tests contained more than 2 micrograms/g of Der p I and Der f I. The probability that house-dust samples of class 2 contained more than 10 micrograms/g of mite allergens was 88%; it was 100% for house-dust samples of class 3. The probability that a house-dust sample of class 0 contained less than 2 micrograms/g of mite allergen was 87%. For each level of mite allergen, a ROC curve was constructed with the true positive rates and the false positive rates calculated by different cutoffs of guanine concentration. The cutoff point which gave the best compromise between sensitivity (76%) and specificity (89%) was 2100 micrograms/g for the threshold of 2 micrograms/g of Der p I and Der f I. For detection of a mite allergen > 10 micrograms, a guanine content of 3000 micrograms/g gave the best compromise between sensitivity (86%) and specificity (93%). In conclusion, the guanine test represents a satisfactory environmental test, inexpensive and simple, for predicting mite allergen levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Mite allergen content in mattress dust of Dermatophagoides-allergic asthmatics/rhinitics and matched controls

It has been suggested that the mites Dermatophagoides pteronyssinus and D. farinae are important indoor environmental factors facilitating both the sensitization of atopic subjects and asthmatic attacks of house dust-sensitive patients. Contradictory results have been reported about the current exposure to mites or their allergens among patients and control groups of atopic or non-atopic subjects. In order to determine whether there is a difference in mite exposure levels between D. pteronyssinus-sensitized asthmatics and/or rhinitis and control subjects we considered a case-control study of 70 patients with asthma and/or rhinitis and positive skin test reactions to D. pteronyssinus and twice as many control subjects who were matched as to age and sex. The first control subject for each patient was an immediate neighbour of the patient and the second was patient arbitrarily chosen among hospitalized patients. Mite allergen exposure was measured in mattress dust collected under standardized conditions, by measuring Der p I+Der fI content and by performing a semiquantitative guanine determination (Acarex-test). The content of Der p I and Der fI was very high both in the homes of patients and those of healthy individuals: 69% of the total samples contained more than 10 micrograms Der pI+Der fI/g of dust. There was no significant difference between cases and controls with respect to Der p I, Der fI, Der p I+Der fI content and Acare class distributions. The calculated odds-ratios associated with the Acarex test and the mite allergens did not differ significantly from the level 1.0.(ABSTRACT TRUNCATED AT 250 WORDS)

Allergens and asthma

This article presents the studies that show that asthma in children is strongly associated with sensitization to dust mite and other indoor allergens. In addition, the recent evidence that this association reflects a causal relationship between allergen exposure and asthma is reviewed. The relevance of quantitative measurements of the major indoor allergens (dust mite, cockroach, and cat) in the houses of children with asthma is discussed. Finally, the increasing evidence that avoidance measures can be an effective treatment for asthma is considered together with the details about avoidance protocol for dust mite and cat allergen.

Identification of allergenic epitopes on Der ⨍ I, a major allergen of Dermatophagoides farinae, using monoclonal antibodies

The antigenic and allergenic structure of Der f I, a major allergen of the house dust mite Dermatophagoides farinae (Df) was investigated by means of a panel of 11 selected monoclonal antibodies (mAb) obtained from BALB/c mice immunized with purified Der f I. The species specificity of these mAb, tested with Der f I and Der p I--the homologous allergen from Dermatophagoides pteronyssinus--was generally restricted to Der f I since 10 out of 11 mAb reacted only with this allergen. Epitope specificity of the mAb was determined by both competitive inhibition and sandwich ELISA experiments. The results indicated the presence of at least four non-overlapping, non-repeated antigenic sites on Der f I, which were recognized by one or several mAb (sites A, B, C and D). Comparative epitope specificity studies between human IgE antibodies and mice mAb were performed, on sera and basophils of Df sensitive patients, using different inhibition assays (ELISA and histamine release experiments). The degree of inhibition varied between the patients and upon the assay design. Most of the mAb tested were found to significantly inhibit the binding of human IgE to Der f I (p less than 0.01) when compared with Der p I specific mAb as a control. The mAb reacting with site A was found to be the most potent inhibitor, presenting a mean inhibition of up to 56% in ELISA as well as in histamine release experiments. The results show that both human IgE antibodies and mAb can be directed against identical or closely related epitopes of Der f I. Therefore anti-Der f I mAb constitute immunologic probes in further allergenic epitope and peptide analysis of this major mite allergen.

Domestic endotoxin exposure and clinical severity of asthma

Endotoxins are potent pro-inflammatory substances present in several natural environments and in commercial house dust extracts. To investigate the possible effect of chronic endotoxin exposure on asthma, 28 patients with perennial chronic asthma (20 allergic to house dust mite and eight intrinsic asthmatics) were evaluated during a 4-month period (lung function, clinical and immunological criteria). At the same time, two house dust samples were collected from each patient's home to determine total house dust weight (mg/m2), endotoxin concentration and house dust mite antigen content (evaluated indirectly by guanine content with HPLC method). The mean (+/- s.d.) endotoxin concentration, as measured by quantitative Limulus assay was 2.59 (+/- 3.41) ng/mg house dust, ranging from 0.12 to 20 ng/mg. The mean guanine content was 0.13 (+/- 0.16) mg/100 mg house dust. There was no correlation between endotoxin and house dust mite concentrations. Patients were compared according to the low or high grade exposure to dust, endotoxins and guanine. Compared with patients with low grade (less than or equal to 5.6 ng/ml) exposure, subjects exposed to high endotoxin concentrations (greater than 5.6 ng/ml) showed a significant increase in dyspnea (median 2.6 vs 3.3; P less than 0.05) and treatment (median 14 vs 44.3; P less than 0.01) scores, oral corticosteroid (median 0.0 vs 13.5 mg/24 hr; P less than 0.01) and beta 2-mimetics (median four vs eight puffs/day; P less than 0.01) intake, and a significant decrease in FEV1/FVC (median 84.5 vs 67% of predicted value; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Acarex test correlates with monoclonal antibody test for dust mites

Forty-two dust samples from the homes of patients having positive mite skin tests were tested by both monoclonal antibody and Acarex techniques. A Spearman's correlation coefficient of 0.85 (p = 0.0001) was found. The Acarex test is simple to use and is much less expensive than the monoclonal antibody method. The use of either method may enhance patient compliance with mite-control instructions and may prove crucial to the effective use of miticides in infested homes.