Exposure to indoor allergens and development of allergy

House dust contains several indoor allergens which can elicit hypersensitivity and various atopic symptoms, especially in childhood. This review article focusses on house dust mite hypersensitivity to one of the most important species, Dermatophagoides , as a model. A clear dose-response relationship has been demonstrated between house dust mite allergen exposure in mattress dust samples and sensitization, i.e. serum IgE to Dermatophagoides and positive histamine release from basophil leukocytes to one of the major allergens from Dermatophagoides pteronyssinus, Der p I. 2 μg major allergen of Dermatophagoides /g of dust and 8 μg major allergen of cat/g of dust have been suggested to be threshold concentrations above which the risk of sensitization in genetically predisposed atopic children is significantly increased. Epidemiological studies showed house dust mite allergens to be one of the most important risk factors in the development of atopic airway disease. A relation between age at onset of the first wheezing episode and house dust mite allergen exposure at the age of 1 year has been observed. There are various factors influencing house dust mite growth, and many studies have been performed to reduce house dust mite allergen exposure. Until now, none of the approaches appeared to have achieved sufficient mite and mite allergen reduction.     

Vacuum cleaning decreases the levels of mite allergens in house dust

To investigate the capacity of chemical treatment of surfaces and the difference in capacity among common vacuum cleaners to reduce mite allergen content in house dust, we recruited 52 families with allergic children. Ten families used their central vacuum cleaners. Forty-two families were randomly divided into four groups with 10 or 11 families in each. These families used cither new vacuum cleaners with either HEPA (High Efficiency Paniculate Air) or micro-filters, or their own vacuum cleaners with either tannic acid or placebo. Dust samples were collected from carpets and upholstered furniture in the living rooms and from the mattresses of the children at Days 0, 7, 21, and 35. Der p I and Der f I allergens were determined by sandwich ELJSA, After one week, tannic acid reduced the concentration of mite allergens/g of dust and the total amount/sampling area by 30% and 34%, respectively (p < 0.05), but there was no significant decrease in relation to placebo. After 5 weeks, central, HEPA- and micro-filter vacuum cleaners decreased the mite allergen concentration by 10–50% (p < 0.05) and the total amount of mite allergen from the investigated areas by 50–85% (p < 0.01). In relation to the placebo group the decrease was significant for HEPA-and micro-filter vacuums (p < 0.05), The total amount of mite allergens/ sampling area was more significantly (p < 0.05) reduced than the con-centration/g of dust. We conclude, that tannic acid reduces mite allergen concentrations in dust and total amount/sampling area for a short period of time. Central, HEPA- or micro-filter vacuum cleaners reduce mite ellergen concentrations and still more the total amount of mite allergen in house dust when used regularly for long periods. Therefore, when the total house is thoroughly cleaned, tannic acid should be applied to car pets and upholstery and low mite allergen levels maintained by using modern vacuum cleaners.     

Concentrations of cat (Fel d 1), dog (Can f 1) and mite (Der f 1 and Der p 1) allergens in the clothing and school environment of Swedish schoolchildren with and without pets at home

To investigate whether our hypothesis that cat and dog owners bring allergens to public areas in their clothes was true or not, we studied the levels of Fel d 1, Can f 1, Der p 1 and Der f 1 in dust from the clothes and classrooms of children in a Swedish school. We also investigated the levels of allergen in different areas in the four classrooms used by the children. Thirty-one children were selected in four classes, forming three groups: cat owners, dog owners and children without a cat or dog at home. Furthermore, a group of children with asthma was included. Cat and dog allergens were detected in all 57 samples from clothes and classrooms. Mite allergen Der f 1 was detected in low concentrations in 6 out of 48 and Der p 1 in 5 out of 46 samples investigated. The concentrations of Can f 1 were higher than those of Fel d 1 in samples from clothes (geometric mean: 2676 ng/g fine dust and 444 ng/g) and classrooms (Can f 1: 1092 ng/g, Fel d 1: 240 ng/g). The dog owners had significantly higher concentrations of Can f 1 (8434 ng/g fine dust) in their clothes than cat owners (1629 ng/g, p <0.01), children without cat or dog (2742 ng/g, p < 0.05) and children with asthma (1518 ng/g, p < 0.001). The cat owners did not have significantly higher levels of Fel d 1 (1105 ng/g) in their clothes compared to the other three groups (D: 247 ng/g, nCnD: 418 ng/g, A: 386 ng/g) but the levels were significantly higher than for all children without a cat at home (345 ng/g, p < 0.05). No concentrations of mite allergen and low concentrations of Fel d 1 and Can f 1 were found in the children's hair. There were significantly higher concentrations of Fel d 1 and Can f 1 in dust from curtains than in samples from floors and bookshelves (p < 0.05). There was no significant difference between the allergen concentrations in samples from curtains and from desks and chairs, including the teachers' chairs, the only upholstered furniture in the rooms. Our results support the hypothesis that cat and dog owners bring allergens to public areas in their clothes and support other studies showing that textiles and upholstered furniture function as reservoirs of cat and dog allergens. Thus, children with asthma and other allergic diseases will be exposed to cat and dog allergens at school and by contact with pet owners, even if they avoid animal allergens at home.     

Cat and dog allergen in mattresses and textile-covered floors of homes which do or do not have pets, either in the past or currently

The aim of this study was to measure the levels of cat and dog allergen in homes of families that had either never kept pets or kept or had kept cats or dogs. From a small residential area outside Stockholm consisting of 250 houses with similar exteriors 70 homes were included. Dust samples were collected from mattresses and textile-covered floors. The levels of cat and dog allergen were analysed by ELISA. Fel dl was found in mattress dust in all 70 homes, median 0.5 μg/g [0.24–8.89 μg/g (quartiles)] and textile-covered floors 0.7 μg/g (0.20–2.52 μg/g). Can fl, was found in 98% of the collected samples, mattress dust 1.89μg/g (0.70–9.20 μg/g) and textile-covered floor dust 2.5 μg/g (1.04–2.72 μg/g). There was a positive correlation (p < 0.001) between allergen levels in dust from mattresses and textile-covered floors for both Fel dl(r = 0.68) and Can fl (r = 0.78). The highest levels of cat and dog allergen were found in homes with furred pets (p < 0.001). A significant (p < 0.001) difference was seen in the levels of Fel dl and Can f 1 between the homes of former pet-owners and homes without pets. In summary; cat and dog allergens are present in homes regardless of whether such animals live in the house or not. Mattresses seem to be an underestimated reservoir for pet allergens even in homes without pets. It is important to note that the homes of former pet owners have much lower levels of allergen than current pet owners.     

House dust mite allergen reduction and allergy at 4 yr: Follow up of the PIAMA-study

Exposure to high allergen levels in early life is a risk factor for the development of allergy. We previously reported limited effects of mite allergen impermeable mattress covers in the prevention and incidence of asthma and mite allergy (PIAMA) cohort at the age of 1 and 2 yr. We now present the results of follow-up at 4 yr objectives. To examine the effects of early reduction of house dust mite (HDM) allergen exposure by means of mattress covers on the incidence of allergy and asthma symptoms in the PIAMA birth cohort at the age of 4 yr. High-risk children (allergic mother) were prenatally recruited and randomly allocated to three groups; receiving mite allergen impermeable mattress covers (n = 416), placebo covers (n = 394) or no intervention (n = 472). At 4 yr of age, atopy was assessed by questionnaire; specific Immunoglobulin E (IgE) to inhalant and food allergens was measured in serum. Dust samples collected from the children's mattresses were analysed for mite allergens. Dermatophagoides farinae1 allergen (Der f 1) levels in dust were reduced in the active group. However, Dermatophagoides pteronissinus 1 (Der p 1) levels, sensitization and atopic symptoms were similar in all groups. We found no effect of mite allergen impermeable mattress covers on sensitization and atopy at 4 yr. Moreover, the allergen reducing effects of the covers had disappeared for one of the two mite allergens that were measured.     

Prenatal exposure to mite and pet allergens and total serum IgE at birth in high-risk children

To examine the relationship between prenatal exposure to mite, cat and dog allergens and total serum IgE at birth in newborns at high risk of asthma. In the homes of 221 newborns with at least one first-degree relative with asthma, concentrations (ng/g dust) of allergens of house dust mite (mite), cat and dog were measured at the fourth to sixth month of pregnancy in dust samples from the maternal mattress and living room. At day 3-5 after birth, total IgE was measured in capillary heel blood. A total number of 174 blood samples were available (11 mothers refused newborn's blood sampling, and in 36 cases the blood sample was too small for analysis). In 24% of the newborns, total IgE was elevated (cut-off value 0.5 IU/ml). A significant dose response relationship was found between increasing mite allergen levels [divided in quartiles ng/g dust (qrt)] and the percentage of elevated IgE: first qrt (0-85 ng/g) 13%; second qrt (86-381) 19%; third qrt (382-2371) 26%; fourth qrt (> or =2372) 42%, respectively, p=0.01. This relationship remained significant after adjusting for passive smoking, maternal and paternal mite allergy, socio-demographic factors, birth characteristics and (breast) feeding practice in the first week of life. In high-risk newborns, prenatal exposure to mite allergens, but not to cat and dog allergens from dust of the living room and of the maternal mattress was associated with total serum IgE at birth.     

Domestic aeroallergen levels in Barcelona and Menorca (Spain)

Exposure to common indoor allergens is known to be associated with sensitization and triggers of asthma. Levels of allergens have been barely described in Mediterranean countries. This study reports domestic allergen levels among the general population of two regions of Spain. Dust samples were collected from living rooms and mattresses in homes of infants in Barcelona (n = 366) and Menorca (n = 475) and assayed for house dust mite ( Der p 1 ) and cat allergen ( Fel d 1 ) concentrations by enzyme-linked immunoabsorbent assay (ELISA). Geometric mean values (95% CI) of Der p 1 were 0.77 µg/g (0.65, 0.92) in living rooms and 0.68 (0.56, 0.82) in children's mattresses in Barcelona, and 9.06 (7.93–10.34) and 3.12 (2.71–3.59) in Menorca, respectively. Fel d 1 levels were 0.37 µg/g (0.31, 0.45) and 0.14 (0.12, 0.18) in Barcelona, and 0.42 (0.35, 0.50) and 0.20 (0.18, 0.24) in Menorca. Home characteristics were not consistently related to levels of aeroallergens in either location. Differences in Der p 1 levels in the two locations indicate that levels cannot be extrapolated from one part of a country to another with any certainty. Additionally, allergen reduction measures related to indoor sources must be specific to each location.     

Seasonal variations in house dust mite allergens--significance for children with allergy

Allergenic proteins of the house dust mites Dermatophagoides pteronyssinus and Dermatophagoides farinae and their major allergens Der p I and Der f I are one of the most significant environmental factors which may facilitate sensitization and allergic airway disease in childhood. In order to measure seasonal variations of mite allergen exposure, we collected mattress dust samples monthly in 13 homes over a period of 1 year. Der p I and Der f I were determined with a sandwich type ELISA. Mite allergen levels were significantly lower from January-June than from July-December (p less than 0.05) which was mostly due to Der p I variations. Only in 6 of the studied homes seasonal variations in mite allergen concentrations according to seasonal variations in outdoor humidity could be observed. In 7 homes mite allergen exposure stayed constant and seemed to depend only on indoor climate factors.     

Indirect contact with pets can confound the effect of cleaning procedures for reduction of animal allergen levels in house dust

To investigate the capacity of common vacuum cleaners and chemical treatment to reduce cat ( Fel d I) and dog ( Can f I) allergen content in house dust, 52 families with allergic children and no pets at home were recruited. Five groups of 10–11 families used their central vacuum cleaners (n = 10), their own old vacuum cleaners plus either tannic acid (n = 10) or placebo (n = 10) applied to carpets and upholstry after the first sample was collected on Day 0 or new vacuum cleaners equipped with either HEPA (high efficiency particulate air)- (n = 11) or micro-filters (n= 10). Dust samples were collected from carpets and upholstered furniture in the living rooms and from the mattresses of the children on Days 0, 7, 21, and 35. Fel d I and Can f I allergens were determined by sandwich ELISA methods. Central, micro-filter and HEPA-filter vacuum cleaners did not reduce the concentrations nor the total amount/sampling area of Fel d I or Can f I. Tannic acid initially reduced (p < 0.05) both the concentration and the total amount of Fel d I by 30% and Can f I by 10%, but only for one week. The levels increased to base-line after 21–35 days. The concentrations of Fel d I increased 10–30 times in homes visited by cats or cat owners. We conclude, that tannic acid treatment reduced pet allergen concentrations and total amounts in dust for one week only. Central vacuum cleaners or vacuum cleaners equipped with HEPA- or micro-filter did not reduce the pet allergen load in homes of allergics. Indirect contacts with cats caused a pronounced increase in cat allergen levels.     

The influence of exposure to house dust mite, cat, pollen and fungal allergens in the home on primary sensitisation in asthma

The homes of 68 atopic asthmatic children were studied to estimate the concentrations of perennial and seasonal aeroallergens (Der pl, Fel d1, grass pollen, tree pollen, Cladosporium , Aspergillaceae and Alternaria ) to which children were likely to have been exposed during their first few months of life, by sampling in the child's month of birth. There was a strong association between the presence or absence of the house dust mite allergen Der p1 in the air with the skin test and IgE antibody test results (p < 0.001), with a similar association for cat allergen Pel d 1 (p < 0.01), when using a low volume sampler (equivalent to the minute tidal volume of a small baby). No significant correlation was found between levels of allergen in carpet dust and air in the same room. There was a strong indication that the presence of a cat at birth was linked with a higher risk of development of allergy to cat, but high levels of Fel d 1 were sometimes found in homes even when there was no cat present, indicating that allergen may be introduced from other sources. The levels of tree pollen were significantly higher in the homes of tree pollen-allergic children than in the homes of patients without this sensitivity (p < 0.01); and the degree of sensitivity, determined by RAST, correlated significantly to the level of tree pollen in the home (p < 0.001). However, no relationship was found between specific sensitivity and the levels of Cladosporium , Aspergillaceae, Alternaria or grass pollen measured in the homes. The effect of high allergen exposure was most prominent in children under 7 yr and not beyond that age.     

Childhood asthma and exposure to indoor allergens: lowmite levels are associated with sensitivity

The prevalence and level of sensitivity to indoor allergens were studied in relation to current exposure at home in 124 children with perennial asthma living in three climatic zones of Sweden. The house dust mite (HDM) allergen levels were higher in the South than in the North (p < 0.001), while cat and dog allergen levels tended to be higher in the North than the South (n. s.). Thirty-four percent of the children were sensitive to the HDM Dermatophagoides pteronyssinus , as determined by IgE antibodies in vitro, 27% were sensitive to D. farinae , 57% to cat and 55% to dog. Sensitivity to HDM was significantly more prevalent in Southern, than in Central and Northern Sweden (p=0.001) where the children were more often sensitive to pets (cat p=0.005, dog p= 0.002). A significant association between the concentration of Der p I and Derf I in the house dust and both the prevalence of sensitivity to HDM and the IgE antibody levels against mites was found even at concentrations well below the commonly suggested risk level for sensitisation of 2 μg/g dust. No relationship was found between pet allergen concentration in the home dust and sensitivity to pets, possibly because of exposure outside home, e. g. in schools and meeting places for leisure activities. Similarly, there was no consistent association between the level of mite or pet allergen exposure at home and asthma severity as judged by symptom and medication score. The study indicates that there is no threshold value for sensitisation to mite allergens in asthmatic children, and therefore, dust allergen levels at home should be kept as low as possible in homes of children at risk for asthma.     

Determinants of indoor allergens in tropical child care centers

Limited data are available about indoor allergen determinants in child care centers (CCCs) especially in the tropics. This information is important epidemiologically and clinically considering many children attend CCCs. The purpose of this study was to determine the allergen concentrations in CCCs and their associations with CCC characteristics and indoor air quality (IAQ). A panel of indoor allergens including Der p 1, Blo t 5, Fel d 1, Can f 1, Mus m 1, Bla g 1 and Asp f 1 were evaluated from dusts vacuumed from classroom floors of CCCs. Allergen levels were assayed with antibody-based bioplex array or enzyme-linked immunosorbent assays. Indoor temperature, relative humidity and air exchange rates were measured and CCC characteristics inspected. Allergen levels were linearly regressed with CCC characteristics and IAQ. The dominant allergens found in classroom floors were Der p 1, Blo t 5 and Fel d 1. Lower indoor temperatures were associated with higher Der p 1 while lower ventilation rates were associated with higher Blo t 5 concentrations. Prevalence of cat owners was found to be a predictor for Fel d 1 concentrations. Full or partial carpeting is associated with higher dust mite allergen levels. These findings provide information for future indoor allergen exposure assessment studies in CCCs and can be used for intervention with regard to allergen avoidance.     

Study on the Prevention of Allergy in Children in Europe (SPACE): Allergic sensitization at 1 year of age in a controlled trial of allergen avoidance from birth

Several studies have demonstrated that early intervention may modulate the natural course of atopic disease. The objective of this study was to prevent sensitization to house dust mite and food allergens, as well as development of atopic symptoms, during infancy. To achieve this we employed the combination of an educational package with the use of mite allergen-impermeable mattress encasings. A multi-center European, population-based, randomized controlled study of children at increased atopic risk [study on the prevention of Allergy in Children in Europe (SPACE)] was performed in five countries (Austria, Germany, Greece, Great Britain, Lithuania) and included three cohorts of schoolchildren, toddlers and newborns. We report on the newborn cohort. A total of 696 newborns were included in Austria, Great Britain and Germany. Inclusion criteria were a positive history of parental allergy and a positive skin-prick test or specific immunoglobulin E (IgE) of ≥ 1.43 kU/l against at least one out of a panel of common aeroallergens in one or both parents. At 1 year of age the overall sensitization rate against the tested allergens [dust mite allergens: Dermatophagoides pteronyssinus and D. farinae ( Der p and Der f, respectively)] and food allergens (egg, milk) in the prophylactic group was 6.21% vs. 10.67% in the control group. The prevalence of sensitization against Der p was 1.86% in the prophylactic group vs. 5% in the control group. In conclusion, we demonstrated, in a group of newborns at risk for atopic diseases, that the sensitization rate to a panel of aero- and food allergens could be effectively decreased through the use of impermeable mattress encasings and the implementation of preventive measures that were easy to perform.     

Comparison between serial skin-prick tests and specific serum immunoglobulin E to mite allergens

Sensitization to dust mite allergens can be determined by means of a skin-prick test (SPT) or by measurement of specific IgE antibodies in serum (sIgE). In our study, concordance of the results of both methods was analyzed on the basis of reproducible SPT results. Three consecutive SPTs were performed on 138 school children (age 6–8 years) at one-year intervals. SIgE was determined at the end of a two-year observation period. Seven common inhalant allergens (Dpt, Df, birch pollens, hazel pollens, grass pollens and cat and dog dander) were analyzed. The majority of subjects with positive SPT reactions to the respective allergen also showed sIgE (Dpt: 82/86; Df: 53/53; cat dander: 31/32; dog dander: 6/9; birch pollens: 29/31; hazel pollens: 22/22; grass pollens: 37/37). A significant correlation between the SPT [weal diameter (P₁) or allergen/histamine ratio (P₂)] and sIgE was found for Dpt (P₁ = 0.004/P₂ = 0.016), birch pollens (P₁ = 0.002/P₂ = 0.0001) and grass pollens (P₁ = 0.0005/P₂ = 0.0001). There was also a significant correlation between sIgE to Dpt and to either Der p 1 (p = 0.0001) or Der p 2 (p = 0.0001), as well as between sIgE of both major allergens (p = 0.0001). In the analysis of co-sensitization of Dpt and Df, most subjects sensitized to Dpt were also sensitized to Df (57/91). Children with sIgE to Dpt (n = 87) usually showed sIgE to Df (n = 83). In this study, SPT and sIgE results are concordant and appear equivalent when using reproducible SPTs. Therefore, in the case of a positive Dpt result, additional testing for sensitization to Df can be regarded as redundant when Dpt and Df are the major contributors to the allergen content of house dust.     

Mites in dust samples from mattress surfaces from single beds or cribs in the south Brazilian city of Londrina

The aim of this study was to investigate the mite fauna in mattresses dust samples from cribs or beds in the south Brazilian city of Londrina, State of Parana. A total of 133 dust samples from upper and lower mattress surfaces, and bed frames were aspirated once from 38 dwellings (18 cribs and 21 beds), and one day nursery (six cribs). A total of 758 mite bodies were counted in slides: 233 (30.7%) from cribs and 525 (69.3%) from beds (p<0.001). House dust mites--mainly Dermatophagoides pteronyssinus, represented 72% and 84% of total mite count in crib and bed dust samples, respectively. The mean HDM body concentration in crib or bed slides were, respectively, 289.9+/-136.7 and 875.0+/-183.6 mites/g. Statistical analysis showed a significantly higher mite bodies count on lower mattress surface compared with upper surface in bed samples only (p=0.025). Data herein show that cribs like mattress have sufficient mite bodies to cause sensitization to humans. The use of mattress covers for cribs and beds should be encouraged in order to avoid allergens exposure.     

Prenatal exposure to house dust mite allergen (Der p 1), cord blood T cell phenotype and cytokine production and atopic dermatitis during the first year of life

This study investigated the influence of prenatal exposure to house dust mite (HDM, D. pteronyssinus) on interleukin (IL)-2, interferon-gamma (IFN-gamma) and IL-4 producing CD4(+) and CD8(+) T lymphocytes in cord blood as well as on the development of sensitization and occurrence of atopic dermatitis (AD) as the first symptom of allergy during the first year of life. Dust samples (n = 22) were collected by vacuum cleaning the maternal mattress during early to mid-pregnancy. In these samples, the amount of the major HDM antigen (Der p 1) was assessed by a sensitive enzyme-linked immunosorbent assay technique (detection limit 0.004 microg/g dust). Flow cytometry was used to determine cord blood lymphocyte subtypes and to quantify the intracellular amounts of IL-2, IFN-gamma and IL-4 produced by cord blood CD4(+) helper and CD8(+) cytotoxic T lymphocytes, both spontaneously and after stimulation with phorbol-12-mirystate-13-acetate and ionomycin. Children were followed for 1 yr for the presence of symptoms associated with allergy. In addition, at the age of 1 yr specific IgE to different classical inhalant and food allergens was measured. Higher prenatal exposure to Der p 1 (>0.2 microg/g dust) was associated with a significant lower percentage of IFN-gamma producing stimulated CD4(+) T lymphocytes, compared with lower prenatal Der p 1 exposure (p = 0.03). The presence of AD during the first year of life (n = 9) was associated with an increased number of naive CD4(+) CD45RA(+) lymphocytes (p = 0.03), with an increased spontaneous IL-4 production by CD8(+) lymphocytes (p = 0.04) and with a decreased percentage of IFN-gamma producing stimulated CD4(+) lymphocytes (p = 0.04). Furthermore, exposure to HDM during pregnancy tended to be higher in mothers of children with AD during the first year of life when compared with those without AD (p = 0.08). This study shows that the level of prenatal exposure to Der p 1 influences the immune profile of cord blood T lymphocytes and the clinical outcome in early life. Therefore, the prenatal environment must be regarded as a possible early risk factors for allergic diseases in children.     

Placebo-controlled study of the mite allergen-reducing effect of tannic acid plus benzyl benzoate on carpets in homes of children with house dust mite sensitization and asthma

We studied the effect of a spray containing 1% benzyl benzoate, an acaricide, and 1% tannic acid (‘Lowal’; a protein‐denaturing substance), on concentrations of major allergens from house dust mite (HDM) species Dermatophagoides pteronyssinus and D. farinae (Der p 1 and Der f 1, respectively) in carpets. In a double‐blind, placebo‐controlled study with crossover design, 30 homes of children with HDM sensitization and asthma were included. All houses showed ≥ 400 ng/g of Der p 1 + Der f 1 in carpet dust. The first treatment was performed on day 0 (group 1 active treatment, n = 15; group 2 placebo treatment, n = 15). After 2 and 8 weeks, dust samples were collected for quantification of mite allergens. After a 2‐week washout period, the second treatment was performed (group 1 placebo treatment; group 2 active treatment). Again, carpet dust was collected after 2 and 8 weeks. Twenty‐two of 30 families completed the trial: 14/15 in group 1 and eight of 15 in group 2. On day 0, there was no significant difference in mite allergen exposure between group 1 and group 2 (1,498 vs. 2,239 ng/g of Der p 1 + Der f 1, respectively). In group 1, the geometric mean for the difference of mite allergen concentration comparing day 0 and week 6 was 196 ng/g (95% CI: ?7,161 and 8,401) for the first treatment (active) and 15 ng/g (95% CI: ?1,079 and 1,292) for the second treatment (control). In group 2, the difference was 66 ng/g (95% CI: ?398 and 1,515) for the first treatment (control) and 609 ng/g (95% CI: 186 and 9,264) for the second treatment (active). Comparing placebo and active treatment in total, there was a significant decrease following placebo treatment after 14 days (p = 0.026). After 8 weeks, active treatment was superior to placebo treatment (p = 0.049), but the allergen reduction achieved was < 20% (median 1,500 ng/g on day 0 vs. 1,250 ng/g after 8 weeks). We conclude that the slight mite allergen reduction on carpets achieved by the treatment with ‘Lowal’ is unlikely to achieve worthwhile clinical benefit either in the treatment of mite‐sensitive patients or in primary or secondary prophylaxis.     

Effects of an acaricide on mite allergen levels in the homes of asthmatic children

Previous study by the current authors has shown that treating homes with D'Allergen, an acaricidal agent, can reduce bronchial hyper-reactivity in asthmatic children with house dust mite allergy. In the present study, the effects of a single D'Allergen treatment on the levels of major dust mite allergens, Der p I and Der f I was evaluated, and the duration of its effectiveness in the environment determined. Twenty randomly selected homes were treated with the acaricide and ten remained untreated. Dust samples were collected from mattresses, upholstered sofas and carpets of these homes before and 1, 2 and 4 months after treatment. The samples were then assayed for Der p I and Der f I allergens using a sandwich enzyme immunoassay. The results showed that D'Allergen was effective in reducing dust mite allergen levels in all three niches by 1.5–22.3 times below baseline values. This effect, however, was only present for 2 months, and the dust mite allergen levels increased to those of the baseline by the fourth month after treatment. These results indicated that repeated applications of the acaricide were required at 2–3 monthly intervals to obtain optimal effectiveness.     

Predictive features for persistence of atopic dermatitis in children

Allergen exposure plays an important role in atopic dermatitis (AD). Because immunological mechanisms underlying asthma and AD have great similarities, we evaluated whether features such as allergen sensitization, immune response, disease severity and duration or allergen exposure could be considered predictive for AD persistence. Seventy-one AD children (age range 14–158 months) were enrolled and followed for 3 consecutive years for AD severity using the SCORAD index (SI). At enrollment, reactivity to inhalant and food allergens using the skin prick test (SPT) and house dust mite (HDM) atopy patch test (APT), and HDM allergens in house dust were evaluated. After 3 years, 38 children outgrew their AD (AD^– group), while in 33 AD persisted (AD⁺ group). At enrollment, AD⁺ children had a higher SI, higher rate of positivity to SPT and APT for mites (p = 0.001), and higher environmental exposure to HDM allergens (p = 0.035). The AD⁺ children developed more respiratory symptoms in comparison to AD^– children (p < 0.001). None of the AD^– children presented APT positivity. In our study population, positivity of SPT and APT for HDM, environmental allergen exposure levels and severity of the disease at enrollment presented a significant predictive power towards AD persistence. Subjects with positive skin reactivity to HDM should be considered at risk of AD persistence and of possible development of allergic respiratory disorders.     

Fetal peripheral blood mononuclear cell proliferative responses to mitogenic and allergenic stimuli during gestation

Blood samples were obtained from fetuses and premature babies (n=51) (15-34 weeks gestation) to determine at what stage the fetal immune system was able to produce a positive proliferative response to common allergens. Peripheral blood mononuclear cells (PB MC) were stimulated with the mitogen, phytohaemagglutinin (PHA), and the allergens, house dust mite, cat fur. birch tree pollen, β-lactoglobulin, ovalbumin and bee venom (mellitin). Results were expressed as ratios of stimulated to unstimulated ³H thymidine incorporation, and as percent positive responders. There was an increase in proliferation ratio which correlated with increasing gestational age for PHA (p < 0.0001), cat fur (p=0.042), birch pollen (p=0.022) and β-lactoglobulin (p=0, 006). The point in gestation when cells from some individuals began responding to the allergens with a ratio of 2. 0 was at approximately 22 weeks. PBMC proliferative response ratios were higher from samples from babies > 22 weeks gestation compared to < 22 weeks for the mitogen and all allergens, except mellitin. There was also a greater proportion of positive responders from samples > 22 weeks compared to < 22 weeks for the mitogen and all allergens, except mellitin. Maternal exposure to birch pollen, which has a discrete season, was assessed to determine whether exposure had occurred at 22 weeks gestation or beyond. Results showed a higher prolifera tive response in infant cells stimulated with birch pollen (p=0.005) and higher proportion of positive responders (p=0.01) in the group of babies whose mothers had been exposed to hirch pollen beyond 22 weeks, compared to those whose mothers had not been so exposed. These results suggest that in utero fetal exposure to an allergen from around 22 weeks gestation may result in primary sensitisation to that allergen, leading to positive proliferative responses, at birth.