The role of indoor allergen exposure in the development of sensitization and asthma

The role of indoor allergen exposure in the development of sensitization and asthma remains a subject of controversy. From a number of cross-sectional and longitudinal studies we can conclude that there is a very close association between allergen exposure and the sensitization of an individual. The dose-response relationships seem to differ between allergens; house dust mite and cockroach allergens appear to have a positive linear relationship, whereas cat allergens appear to act quite differently, with maximum sensitization developing at moderate exposure levels. Very low levels of cat allergen exposure are likely to induce no response and very high levels are likely to develop a form of tolerance, with a modified T helper cell type 2 response and the production of IgG4 antibodies and but not IgE. The relationship between indoor allergen exposure and asthma is, however, less clear. The proposed mechanism for the development of disease is that allergen exposure causes sensitization, and continued exposure leads to airway responsiveness and inflammation. As yet, the evidence for allergen exposure being a primary cause of asthma remains weak, and the results of ongoing prospective, randomized allergen avoidance trials are awaited to clarify this issue.     

Serum IgG and IgG4 antibodies to Fel d 1 among children exposed to 20 microg Fel d 1 at home: relevance of a nonallergic modified Th2 response

Exposure to foreign antigens is an essential element of all immune responses, including allergic sensitization. For some allergens (e.g. mite and cockroach), the prevalence of sensitization is directly correlated with exposure. However, for allergens derived from domestic animals, several studies have suggested that children with a cat in the home have a decreased risk of sensitization and asthma. We have now shown that many children exposed to greater than 20 microg of Fel d 1/g of dust at home made an IgG and IgG4 antibody response to Fel d 1 without IgE antibody. This modified Th2 response is not associated with symptoms and should be regarded as a form of immunological tolerance. The fact that the dose-response relationship between cat exposure and sensitization is bell shaped, while that for mite exposure and sensitization is linear, is highly relevant to understanding the role of allergens in the increase in allergic disease.     

Monitoring allergen exposure in asthma: new treatment strategies

The development of monoclonal antibody-based enzyme-linked immunosorbent assay technology for measuring environmental allergen exposure has provided a benchmark for assessing the role of indoor allergens in causing asthma and other allergic diseases. Epidemiological studies from several parts of the world have shown that immunoglobulin E (IgE)-mediated sensitization to indoor allergens (mite, cat, dog and cockroach) is a risk factor for asthma attacks. A dose-response relationship between allergen exposure and sensitization has been demonstrated for mite allergens, and threshold values for exposure levels leading to sensitization or to exacerbations of symptoms have been defined. Comparative studies on airborne allergen levels have made it possible to determine the properties of aeroallergen particles, their concentration in indoor air, and the relationship to clinical symptoms. Together, these studies provide strong evidence that allergen exposure plays a causal role in the development of bronchial hyperreactivity and of the chronic inflammatory responses seen in patients with asthma. Logically, the primary preventive treatment should be allergen avoidance. Through knowledge of indoor allergen levels, both in dust and in the air, different avoidance strategies have been applied to the various indoor allergens, and there is increasing evidence of their clinical efficacy. Monitoring allergen levels in patients' houses should improve their understanding of the role of allergens in asthma and improve compliance with avoidance measures.     

Allergen exposure in infancy and the development of sensitization, wheeze, and asthma at 4 years

BACKGROUND: The relationship between mite and pet allergen exposure in infancy and the subsequent development of sensitization and asthma is complex. OBJECTIVE: We prospectively investigated the effect of allergen exposure at 3 months of age on the development of sensitization, wheeze, and physician-diagnosed asthma in the first 4 years of life in a birth cohort of children with and without an atopic mother. METHODS: Children participated in the Prevention and Incidence of Asthma and Mite Allergy study. Allergen exposure at 3 months of age was determined from mattress dust samples. Specific IgE to inhalant allergens was measured at 4 years of age, and information about wheeze and physician-diagnosed asthma was collected with yearly questionnaires. RESULTS: Mite and cat allergen exposure in infancy were associated with an increased risk of specific sensitization to house dust mite and cat, respectively, at 4 years of age. There were borderline significant associations between cat allergen exposure and persistent wheeze in the total study population and between dog allergen exposure and persistent wheeze in children with a nonatopic mother. In children with an atopic mother, there was some indication of a positive association between mite allergen exposure and physician-diagnosed asthma. CONCLUSION: Early house dust mite and cat allergen exposure might lead to sensitization and, in case of cat allergen exposure, to persistent wheeze. Early mite and dog allergen exposure might lead to asthma and persistent wheeze, respectively, but only in subgroups defined by maternal atopy.     

Environmental prevention in atopic eczema dermatitis syndrome (AEDS) and asthma: avoidance of indoor allergens

 Indoor allergens represent an important precipitating factor for both asthma and atopic eczema dermatitis syndromes (AEDS). There is also accumulating evidence that sensitization to those allergens is associated with the onset of atopic disorders. Patients with AEDS present aeroallergen-specific T-cell responses associated with worsening of symptoms when exposed to specific aeroallergens. Furthermore, application of indoor allergens to the skin of patient with AEDS induces a local eczematous response in one-third of these patients. Exposure to high concentrations of mite allergens in early infancy have been demonstrated to be a risk factor for developing atopic dermatitis during the first 3 years of life. Moreover, a clear dose–response relationship has been documented between mite exposure and disease activity. Primary prevention of AEDS by avoiding indoor allergen exposure has been proved to be effective only when allergenic foods have also been avoided. Mite allergen avoidance in infants with AEDS and food allergy may however, prevent mite sensitization and the onset of asthma. Indoor allergen avoidance has been demonstrated to be effective in the majority of studies performed in patients with established AEDS. Negative results may be explained either by individual susceptibility variation, by long duration of disease with the consequent irreversible pathological changes in the target tissue or by exposure to allergens outside the house. Education of the patients and public consciousness of the problems are crucial for the efficacy of indoor allergen avoidance in allergic diseases.     

Cat and dust mite sensitivity and tolerance in relation to wheezing among children raised with high exposure to both allergens

BACKGROUND: Recent evidence has suggested that high exposure to cat allergens is associated with decreased prevalence of sensitization to cat and, in some studies, decreased asthma. OBJECTIVE: Our objective was to study antibodies to cat and mite allergens and their relationship to wheezing in a country with high exposure to both allergens. METHODS: Sera from 112 wheezing and 112 control children aged 10 to 11 years in a nested case-control study in New Zealand were assayed for specific IgE antibody, as well as IgG antibody and IgG4 antibody, to Der p 1 and Fel d 1. RESULTS: IgE antibody to both mite (99/224) and cat (41/224) were strongly associated with wheezing (odds ratios, 5.2 and 6.5, respectively). Children who had ever lived with a cat were less likely to have IgE antibody to cat (20/141 vs 21/83, P < .04); however, cat ownership had no effect on IgE antibody to mite (67/141 vs 32/83, P = .23). Among sensitized children, cat ownership was associated with a lower prevalence of IgE antibody to cat (28% vs 66%, P < .001), and this analysis remained significant after exclusion of children whose families had chosen not to own a cat. Among sensitized subjects, the mean titer of IgE antibody to cat (1.7 IU/mL) was 10-fold lower than for mite (22.1 IU/mL). A cat in the home had no significant effect on endotoxin or mite allergen in house dust, whereas cat allergen was much higher (40.8 vs 3.3 microg/g). CONCLUSION: The response to these 2 allergens was distinct on the basis of the prevalence of sensitization, the titer of IgE antibody, and the effect of cat ownership. The results suggest that induction of tolerance to cat allergen is an allergen-specific phenomenon that cannot be attributed to endotoxin or family choice. The strength of the IgE antibody response to dust mite in humid climates could contribute to the increased prevalence and severity of asthma.     

Intranasal air sampling in homes: relationships among reservoir allergen concentrations and asthma severity

BACKGROUND: The relationship among inhaled allergen exposure, sensitization, and asthma severity is unknown. OBJECTIVES: To investigate the relationship among personal allergen exposure, reservoir dust allergen concentrations, and physiological measures of asthma severity; to examine the numbers of particles inspired that react with autologous IgE and IgG4. METHODS: A total of 117 patients with asthma wore 5 nasal air samplers (NASs) at home: 1 each for exposure to mite, cat and dog allergens, NAS-IgE, and NAS-IgG4. NASs were processed by HALOgen assay for allergen measurement and incubated with autologous serum for detection of NAS-IgE and NAS-IgG4. Reservoir allergen concentrations were measured by ELISA. Subjects' asthma severity was ascertained by measurement of lung function, exhaled nitric oxide, and nonspecific bronchial reactivity to histamine. RESULTS: Nasal air sampler counts correlated with reservoir concentrations for cat (r=0.31; P=.001) and dog (r=0.20; P=.03) but not mite allergen (r=0.001; P=1.0). There was no significant relationship between sensitization with exposure measured by NAS to any allergen and PD20FEV1 (F[3,60]=1.60; P=.20); however, sensitization with exposure in dust reservoirs had significant effects on PD20FEV1 for any allergen (F[3,59]=3.12; P=.03), cat (F[3,59]=3.77; P=.01), and mite (F[3,59]=2.78; P=.05), but not dog (F[3,59]=1.06; P=.37). We repeated the analysis with separate variables for sensitization and exposure, controlling for the confounders; sensitization but not exposure conferred lower PD20FEV1 values. However, increasing cat allergen exposure was associated with improving bronchial reactivity in not cat-sensitized patients. NAS-IgE and NAS-IgG4 counts bore no relationship to any measure of asthma severity. CONCLUSION: Nasal air samplers confer no advantage over reservoir dust analysis for studies of asthma severity. CLINICAL IMPLICATIONS: In common with other measures of exposure, single nasal air samples do not provide a useful measure of home allergen exposure for the individual patient with allergic asthma.     

Relevance of allergens from cats and dogs to asthma in the northernmost province of Sweden: Schools as a major site of exposure

BACKGROUND: The prevalence of asthma in the northernmost region of Sweden has been estimated at 6% to 8% in spite of the very dry climate. The causes of the increase in asthma are not clear, but conditions are unfavorable for dust mite growth, and domestic animals are thought to be the primary source of indoor allergens. OBJECTIVES: We sought to investigate the relationship between asthma, exposure, and sensitization in Northern Sweden, with a focus on the role of schools. METHODS: Serum was collected from 110 asthmatic children, 55 children with symptoms of asthma but no established diagnosis, and 63 control children (age, 7 and 8 years). Total IgE and specific IgE to 7 allergens were measured. Dust samples were collected from the classrooms of 7- and 8-year-old children in 22 schools from Kiruna and Lulea, Sweden. For comparison, dust was also collected from 24 homes in Kiruna and 2 schools in Virginia in the United States. RESULTS: Serum IgE antibody assays on 165 children with respiratory symptoms confirmed that there was a high degree of sensitization to cat, dog, and birch in Northern Sweden. Cat and dog allergens were present in almost all of the school samples in Sweden. By contrast, dust mite and cockroach allergens were generally unmeasurable. The highest levels of cat and dog allergens were found in samples from desks and chairs. Cat and dog allergen levels in the schools were comparable with but higher than those in the homes without pets. The schools in Virginia had similar allergen levels, except that samples from this humid region also had significant mite allergen. CONCLUSIONS: In this climate the primary sensitization associated with asthma is to cat dander and dog dander but also to birch pollen. Mite and cockroach allergens were not present in the dust samples, and sensitization to these allergens was not significant. The schools appear to be a major site of exposure to cat and dog allergens. These results are relevant both to an understanding of the reasons for the increase in asthma in this region and to any proposal to reduce exposure to allergens.     

House dust mite and cockroach exposure are strong risk factors for positive allergy skin test responses in the Childhood Asthma Management Program

BACKGROUND: Children with asthma have a high prevalence of environmental allergies, especially to indoor allergens. The relationships of exposure to indoor allergens (dust mites, cat, dog, cockroach, and molds) and other host factors to allergy sensitization have not been evaluated simultaneously in a large cohort. OBJECTIVES: We studied 1041 children aged 5 to 12 years with mild-to-moderate asthma to determine risk factors associated with having positive allergy skin test responses to indoor allergens. Also, we described, compared, and contrasted 6 allergens in the home environments of these children from 8 North American cities. METHODS: Data were used from baseline visits of the Childhood Asthma Management Program. Patients' sensitivities to house dust mites (Dermatophagoides farinae and Dermatophagoides pteronyssinus), cats, dogs, cockroaches, and molds were examined for relationships to demographic variables, home dust allergen exposures, number of other positive allergy skin test responses, total serum IgE levels, and smoking in the home. RESULTS: San Diego (78.5%) and Toronto (59.3%) had the topmost percentages of homes with moderate-to-high house dust mite levels. Boston (21.5%), St Louis (16.3%), and Baltimore (13.4%) had the highest percentages of homes with detectable levels of cockroach allergen. For house dust mites, the higher the level of allergen exposure, the more likely patients were to have positive allergy skin test responses, with relative odds of 9.0 (95% confidence interval, 5.4-15.1) for those exposed to high mite levels (>10.0 microg/g dust) relative to those unexposed. Even exposure to low levels of mite allergen (0.020-2.0 microg/g) was found to be a significant risk factor for sensitization. For cockroach allergen, those with detectable home exposure were more likely to have positive skin test responses (relative odds, 2.2; 95% confidence interval, 1.3-3.8) than those with undetectable exposure. In contrast, levels of exposure to cat, dog, and mold allergens were not related to sensitization rates. For cat allergen, this may reflect lower rates of cat ownership among highly sensitized subjects. Furthermore, the number of allergy skin test responses that were positive, excluding the test for the outcome of interest for each model, and total serum IgE levels were strong independent predictors of sensitization. CONCLUSIONS: Levels of exposure determined by house dust analysis are important determinants of sensitization for dust mite and cockroach allergen. This relationship was not demonstrable for cat, dog, or mold allergens, possibly because of confounding factors. For all allergens studied, the degree of atopy, determined by the total number of positive skin test responses or by total serum IgE levels, is an important contributing risk factor for sensitization.     

An experimental model of allergic asthma in cats sensitized to house dust mite or bermuda grass allergen

BACKGROUND: Animal models are used to mimic human asthma, however, not all models replicate the major characteristics of the human disease. Spontaneous development of asthma with hallmark features similar to humans has been documented to occur with relative frequency in only one animal species, the cat. We hypothesized that we could develop an experimental model of feline asthma using clinically relevant aeroallergens identified from cases of naturally developing feline asthma, and characterize immunologic, physiologic, and pathologic changes over 1 year. METHODS: House dust mite (HDMA) and Bermuda grass (BGA) allergen were selected by screening 10 privately owned pet cats with spontaneous asthma using a serum allergen-specific IgE ELISA. Parenteral sensitization and aerosol challenges were used to replicate the naturally developing disease in research cats. The asthmatic phenotype was characterized using intradermal skin testing, serum allergen-specific IgE ELISA, serum and bronchoalveolar lavage fluid (BALF) IgG and IgA ELISAs, airway hyperresponsiveness testing, BALF cytology, cytokine profiles using TaqMan PCR, and histopathologic evaluation. RESULTS: Sensitization with HDMA or BGA in cats led to allergen-specific IgE production, allergen-specific serum and BALF IgG and IgA production, airway hyperreactivity, airway eosinophilia, an acute T helper 2 cytokine profile in peripheral blood mononuclear cells and BALF cells, and histologic evidence of airway remodeling. CONCLUSIONS: Using clinically relevant aeroallergens to sensitize and challenge the cat provides an additional animal model to study the immunopathophysiologic mechanisms of allergic asthma. Chronic exposure to allergen in the cat leads to a variety of immunologic, physiologic, and pathologic changes that mimic the features seen in human asthma.     

Food allergy promotes a Th2/Th17 response that drives house dust mite-induced allergic airway inflammation in humanized mice

Food allergy is related to increasing risk of the development of allergic asthma, but the precise interplay between sensitization to different allergens in different compartments of the body is not fully understood. The aim of this study was to develop a novel humanized murine model of mixed food and respiratory allergy that recapitulates the human anaphylactic response and to more clearly understand the impact of food allergies on asthma. Immunodeficient mice transferred with peripheral blood mononuclear cells (PBMCs) from donors with peanut and house dust mite (HDM) allergy were exposed and challenged to peanut. Between peanut exposure and challenge, mice were intranasally treated to HDM. Allergic parameters were analyzed. Allergen-specific immunoglobulin (Ig)E in sera could only be measured in mice treated with peripheral blood mononuclear cells (PBMCs) plus allergen. A preceding peanut exposure increased IgE levels, histamine release, bronchial hyper-responsiveness and lung inflammation. Recruitment of inflammatory cells to the airways was aggravated associated with an enhanced T helper type 2 (Th2)/Th17 cytokine secretion when the two allergies were present. A preceding peanut exposure amplifies allergic asthma in this humanized model, which may contribute to the understanding of underlying immunological mechanism of polysensitization occurring in allergic individuals and evaluation of therapeutic interventions.     

Epidemiology of the relationship between exposure to indoor allergens and asthma

A very high prevalence of immediate hypersensitivity to common indoor allergens can be demonstrated among children and young adults, with asthma. Recent progress in the immunochemistry of cat, dust mite and cockroach allergens has made it possible to measure exposure to these allergens and to start to define threshold levels of exposure which increase the risk of sensitization and symptomatic asthma. Indeed, it is already clear that exposure to greater than 2 micrograms group I dust mite allergen (or 100 mites) per gram of dust increases the risk of children developing sensitization and asthma. Furthermore, from studies on patients presenting to emergency rooms with asthma, it is clear that the risk of sensitization to allergens derived from cats or cockroaches or grass pollen is restricted to patients who are exposed to high levels of these allergens. Given the increasing morbidity and mortality of asthma it is clear that therapeutic efforts should be focused on identifying relevant allergens and advising patients about techniques for reducing exposure.     

A randomized controlled trial of mite allergen-impermeable bed covers in adult mite-sensitized asthmatics

BACKGROUND: Mite-allergic patients with allergic disease should benefit from avoiding mite allergens. Many physicians, however, are yet to be convinced that allergen avoidance can make a significant contribution to asthma management in these patients. Many allergen-avoidance regimes include multiple measures of allergen reduction, but as mite exposure in the home is most likely to be greatest in bed dust, bedding is usually the first target for intervention. OBJECTIVE: This study selected adult patients considered to be most likely to benefit from avoiding mite allergens, namely diagnosed asthmatics, sensitized to house dust mites and exposed to mite allergen in their mattresses. Patients were randomized into a placebo-controlled trial of the use of allergen-impermeable bed covers for 12 months, without any other form of mite-reduction measures. METHODS: Adults with asthma were selected from general practices and asthma clinics in south-east London. Their serum IgE to mite allergens and allergen content of mattress dust samples were measured. Those with >0.70 kU/L mite-specific IgE and >2 microg/g Der p 1 were randomized into active or placebo treatments. Information was collected on allergic symptoms and medication use and quarterly peak flow diaries were kept throughout the trial. Dog or cat allergic patients were excluded if they had a pet at home to which they were sensitized. RESULTS: The mean decrease in microg/g Der p 1 was 25.7 (95% CI 8.9, 74.1) in the active group and 4.5 (95% CI 1.8, 11.5) in the placebo group. Der p 1 concentrations in the active and placebo groups at the end of the trial were not significantly different. There was no effect on peak flow or asthma symptoms in a simple comparison of the treatment and placebo groups. CONCLUSION: In this group of patients, mite allergen avoidance in the bed by the use of allergen-impermeable bedding alone cannot be recommended as an effective way of relieving asthma symptoms.     

Anti-IgE efficacy in murine asthma models is dependent on the method of allergen sensitization

BACKGROUND: Murine models used to delineate mechanisms and key mediators of asthma have yielded conflicting results and suggest that the dominant mechanism and mediators required for disease induction differ depending on the model and method of allergen sensitization used. OBJECTIVE: The goal of this study was to determine whether the mode of allergen sensitization influenced the role that IgE had in allergen-induced pulmonary eosinophilic inflammation. METHODS: Mice were exposed to dust mite extract in 2 models of allergic inflammation that differed in the method of sensitization. We compared sensitization by aerosol exposure with and without concomitant human respiratory syncytial virus infection with sensitization by means of systemic (intraperitoneal) exposure with adjuvant. After sensitization, animals were similarly challenged with aerosolized allergen. Animals were treated with anti-IgE mAb to deplete IgE and to determine its role in the induction of allergic inflammation and mucosa pathology in these models. RESULTS: Concomitant respiratory syncytial virus infection significantly enhanced allergen sensitization by aerosol exposure and exacerbated eosinophilic inflammation and airway mucosa pathology. Depletion of IgE in this model significantly reduced lung eosinophilic inflammation and airway mucosa pathology. However, in the model in which animals were sensitized by means of systemic allergen exposure with adjuvant, depletion of IgE had no ameliorative effect on lung inflammation or pathology. CONCLUSION: We demonstrated that the method of antigen sensitization can delineate the role of IgE in allergen-induced lung inflammation. In a murine model that more closely resembles ambient allergen exposure in human subjects, IgE had a critical role in the pathogenesis of allergic asthma and mucosa pathology. The results parallel the results reported with anti-IgE efficacy in allergic asthmatic human subjects.     

Exposure to birch pollen in infancy and development of atopic disease in childhood

BACKGROUND: The relationship between early allergen exposure, sensitization, and development of atopic disease remains controversial. In 1993, extremely high levels of birch pollen were recorded in Stockholm, Sweden, creating the unique opportunity to study children with different exposures during infancy. OBJECTIVE: We sought to assess the influence of early high-dose exposure to an inhalant allergen (birch pollen) on sensitization and development of atopic disease in children. METHODS: A total of 583 children with atopic heredity born in Stockholm in February through April 1992, 1993, or 1994 were investigated at age 4.5 to 5 years. The children were examined and underwent skin prick testing with inhalant and food allergens. IgE antibodies (RAST) against birch pollen and recombinant birch pollen allergen (rBet v 1) were analyzed in serum. RESULTS: The children born in 1993 (high-dose exposure at 0-3 months) were more often sensitized (ie, positive skin prick test response) to birch pollen than the children born in 1994 (low-dose exposure; 17.8% and 8.8%, respectively; odds ratio [OR], 2.4; 95% CI, 1.2-4.6). A tendency in the same direction was seen for children born in 1992 (high-dose exposure at 12-15 months; OR, 1.7; 95% CI, 0.9-3.2). The results were supported by the RAST analyses. The prevalence of bronchial asthma, allergic rhinoconjunctivitis, and atopic dermatitis did not differ between the birth-year groups. However, the prevalence of pollen- and animal dander-induced allergic asthma was increased in the children born in 1993 (OR, 2.6; 95% CI, 1.2-5.6). An interaction between early high-dose exposure to birch pollen and cat in the household was suggested for sensitization to cat (P =.06). CONCLUSION: Exposure to high levels of birch pollen in infancy increases the risk of sensitization to the same allergen, as well as the risk of allergic asthma.     

Longitudinal study on the relationship between cat allergen and endotoxin exposure, sensitization, cat-specific IgG and development of asthma in childhood--report of the German Multicentre Allergy Study (MAS 90)

BACKGROUND: Controversial data have emerged regarding the question whether cat exposure in childhood favours or decreases the risk of sensitization and allergic airway disease. In a prospective birth-cohort study, we assessed the association between longitudinal cat allergen exposure, sensitization (immunoglobulin E, IgE), IgG antibody (ab) levels to cat and the development of asthma in children up to the age of 10 years. METHODS: Of 1314 newborn infants enrolled in five German cities in 1990, follow-up data at age 10 years were available for 750 children. Assessments included yearly measurements of specific serum IgE to cat and at age 6 and 18 months, 3, 4 and 10 years measurement of cat allergen Fel d 1 in house dust samples. Additionally, Fel d 1-specific IgG ab were determined in 378 serum samples of 207 children. Endotoxin exposure in mattress dust was measured in a subgroup of 153 children at age 10 years. From age 4 years on, International Study of Asthma and Allergy in Childhood (ISAAC) questionnaires were completed yearly in order to assess the prevalence of wheeze and asthma. RESULTS: Serum IgG-levels to cat showed a large variation, however, intraindividually values showed rather constant concentration over a longer time period. The IgG levels at school-age correlated with cat allergen exposure during the first 2 years of life. Specific IgE to cat was clearly associated with wheeze ever, current wheeze and bronchial hyperresponsiveness (BHR), this was also observed for children with specific IgE ab to cat (>0.35 kU/l) plus IgG levels above 125 U/ml. A large percentage of very highly exposed children showed high IgG but no IgE responses to cat, however, not all highly exposed children were found to be protected from sensitization. Children with IgG but without IgE ab to cat showed the lowest prevalence of wheeze ever and current wheeze despite high cat allergen exposure, however, this trend did not achieve significance. While homes of cat owners showed higher Fel d 1 concentrations than homes without cats, homes of cat owners were not found to have higher endotoxin levels in carpet dust samples than homes without cats. CONCLUSIONS: We could confirm that high cat allergen exposure in a cohort with lower community prevalence of cats is associated with higher serum IgG and IgE levels to cat in schoolchildren. Sensitization to cat allergen (IgE) is a risk factor for childhood asthma. While exposure to cat allergen during infancy is associated with sensitization (IgE), only in the very highly exposed children the likelihood of sensitization (IgE) is decreased and high IgG levels to cat without IgE were associated with low risk of wheeze. However, cat-specific IgG ab levels did not protect children with IgE-mediated sensitization from wheeze.     

Allergic sensitization to indoor and outdoor allergens and relevance to bronchial hyperresponsiveness in younger and older subjects

BACKGROUND: Most previous epidemiological studies on the relationship between allergy and bronchial hyperresponsiveness (BHR) have made no distinction between sensitization to indoor and outdoor allergens. We studied the relationship between specific sensitization to allergen and BHR and further assessed whether this was different in young adults and older subjects. METHODS: Specific IgE to indoor allergens (house dust mite and cat) and outdoor allergens (timothy grass and birch) were measured using the CAP System. BHR was defined as PD20 /= 3). Young adults with multiple sensitization had the highest risk of BHR. Subjects who were exclusively sensitized to pollen did not show increased BHR in both age groups. Total IgE had, independently of sensitization, only a significant dose-response relationship with BHR in the oldest age group. CONCLUSIONS: The association between sensitization and BHR is dependent on the nature of the allergen and the level of specific IgE. Furthermore, this study shows for the first time that total IgE is associated with BHR at older ages, independently of sensitization.     

Focus on cat allergen (Fel d 1): immunological and aerodynamic characteristics, modality of airway sensitization and avoidance strategies

The increasing frequency of pet ownership (especially cats) in many industrialized countries has raised the level of exposure to the allergens produced by these animals. Moreover, it is likely that modern energy-saving systems and the wide use of upholstered furniture has resulted in closer contact between cats (and their allergens) and humans. Many different methods have been developed to quantify the main cat allergen (Fel d 1) in settled dust and in ambient air. The threshold levels of cat allergen inducing sensitization or triggering respiratory symptoms in sensitized patients have been calculated in settled dust, but airborne amounts of Fel d 1 probably represent a more reliable index of allergen exposure. Noticeably, the amount of Fel d 1 may be relatively high also in confined environments where cats have never been kept. It has been demonstrated that clothes of cat owners are the main source for dispersal of allergens in cat-free environments. This fact may be of relevance, because recent studies have shown that allergic sensitization to cats is more likely to develop in children exposed to moderate levels of this allergen than in children exposed to high amounts of Fel d 1. The ubiquity of cat allergen may justify the common observation that allergen avoidance is often insufficient to reduce the risk of developing allergic sensitization and/or symptom exacerbation in highly susceptible patients. Further efforts are needed to improve the efficacy of Fel d 1 avoidance strategies to try to reduce the risk of allergic sensitization to this allergen.     

Direct and indirect exposure to pets – risk of sensitization and asthma at 4 years in a birth cohort

INTRODUCTION: There are conflicting data on the association between early exposure to pets and allergic diseases. Bias related to retrospective information on pet ownership has been addressed as a reason for distorted study results. OBJECTIVE: To elucidate how early exposure to cat and dog relates to IgE-sensitization and asthma in children at 2 and 4 years of age, in a prospective birth-cohort study. METHODS: Four thousand and eighty-nine families with children born 1994-1996 in predefined areas of Stockholm answered questionnaires on environmental factors and symptoms of allergic disease at birth, one, two and four years of age. Dust samples collected from the mothers' beds at birth were analysed for Fel d 1 and Can f 1 in a subgroup of the cohort. Blood samples taken at four years from 2614 children were analysed for allergen-specific IgE to common airborne allergens. Risk associations were calculated with a multiple logistic regression model, with adjustment for potential confounders. RESULTS: A correlation was seen between allergen levels and reported exposure to cat and dog. Exposure to cat seemed to increase the risk of cat sensitization, OR (odds ratio) 1.44 (95% confidence interval 1.03-2.01), whereas dog exposure did not have any effect on dog sensitization, OR 1.16 (0.79-1.72). Dog ownership was related to a reduced risk of sensitization to other airborne allergens, OR 0.36 (0.15-0.83), and a similar tendency was seen for cat ownership OR 0.63 (0.37-1.07). Early dog ownership seemed to be associated with a lower risk of asthma, OR 0.50 (0.24-1.03), with no corresponding effect after cat ownership, OR 0.88 (0.56-1.38). CONCLUSION: Early exposure to cat seems to increase the risk of sensitization to cat but not of asthma at 4 years of age. Dog ownership, on the other hand, appears to be associated with lowered risk of sensitization to airborne allergens and asthma. Both aetiological relationships and selection effects have to be considered in the interpretation of these findings.     

Exposure to indoor allergens in homes of patients with asthma and/or rhinitis in southeast Brazil: effect of mattress and pillow covers on mite allergen levels

Background: Exposure and sensitization to indoor allergens have been associated with the development of asthma and other allergic diseases in many parts of the world. It is important to establish the degree of exposure, and to evaluate whether allergen control measures are effective in a particular area. Methods: Concentrations of major allergens of mites, cockroach, cat and dog were measured in dust samples from homes of 24 mite-allergic patients living in Ribeir?o Preto, Brazil. Allergen concentrations were quantitated by monoclonal antibody-based ELISA. Mite-impermeable mattress and pillow covers were applied to beds in the homes of 19 of the 24 patients, and group 1 mite allergen levels were measured 1 and 6 months following intervention. Results: Patients were exposed to high concentrations of mite allergens in their homes. 87.5% of the homes presented concentrations of group 1 allergens >10 microg/g of dust in at least one site. Cockroach allergen concentrations were low in most samples. Dog allergen concentrations were significantly higher in homes with dogs as compared to those without dogs. Mean concentrations of cat allergen were 0.1 microg/g. Mite allergen concentrations in bedding samples dropped from 24 microg/g at baseline to 0.9 and 1.0 microg/g, respectively, 1 and 6 months following encasement of mattresses and pillows. Conclusions: Significant mite allergen reduction can be achieved in an area of high degree of exposure to mite allergens. Further studies evaluating the effect of this reduction on symptoms and airway inflammation will be necessary to establish the effectiveness of mite avoidance measures in our area.