Early exposure to house-dust mite and cat allergens and development of childhood asthma: a cohort study. Multicentre Allergy Study Group

Comparison of quantitative ELISA and semiquantitative Dustscreen for determination of Der p 1, Der f 1, and Fel d 1 in domestic dust samples

BACKGROUND

Quantitative ELISA kits used for the measurement of indoor allergens are time-consuming. Therefore, an immunodot assay (Dustscreen) has been introduced, so that results can be obtained within 4 h. In order to assess the potential applications of the new method, we compared quantitative ELISA methods and Dustscreen.

METHODS

We compared the measurements of the mite allergens Der p 1 and Der f 1, and Fel d 1 by both Dustscreen and one brand of ELISA in 82 dust samples, and we also compared the measurement of the cat allergen Fel d 1 by Dustscreen and a different brand of ELISA in 77 dust samples. Optimum dilutions of dust extracts were compared between the ELISA and the immunodot assay. The nonparametric coefficient of correlation (Spearman's rank) was calculated for each allergen.

RESULTS

The immunodot assay was easy to perform. There was a good correlation between the results of the ELISA and Dustscreen (Der p 1: r=0.98, Der f 1: r=0.93, and Fel d 1: r=0.98). However, the coefficient of variation varied between 50% and 100% for Fel d 1 above 100 000 ng/g in Dustscreen. No cockroach allergen (Bla g 2) was detected in domestic dust samples in Berlin, and lower concentrations of group 2 allergen of mite (from not detectable to 19 500 ng/gm; median concentration 2000 ng/g) were found than mite group 1 allergens (sum of Der p 1 plus Der f 1: median 12 350 ng/g, minimum n.d., maximum 153 120 ng/g).

CONCLUSION

Our results indicate that quantification of indoor allergens in house-dust samples can be performed easily with Dustscreen, and both the technology and methodology are satisfactory.

Risk factors for asthma in urban Ghana

BACKGROUND

Asthma is increasing in prevalence and severity in Africa. Previous studies have suggested that the prevalence of atopy in West Africa was low.

OBJECTIVE

We sought to investigate the risk factors for asthma in Ghanaian school children.

METHODS

Fifty children (age range, 9-16 years) with a physician diagnosis of asthma and asthma symptoms within the previous 12 months and 50 age- and sex-matched healthy control subjects were randomly selected and evaluated by means of questionnaire, skin testing, total and specific IgE measurements, and allergen level measurements from bed dust samples (mite, cat, dog, and cockroach).

RESULTS

Asthmatic children were exposed to higher levels of mite allergens than were control children (geometric mean, 19 microg/g [95% CI, 13.6-26.5] vs. 11.2 microg/g [7.4-15.7]; P <.05). Cat and dog allergen levels were low. There was a marked dissociation between skin test responses and the presence of specific IgE to cat and dog (CAP method). However, 84% of subjects with positive cat dander-specific IgE levels in cat CAP tests and negative skin test responses did not have Fel d 1-specific IgE (chimeric ELISA). In the univariate analysis significant associations with the patient group were found for sensitization to mite (odds ratio [OR], 9.3; 95% CI, 3.7-23.4) and cockroach (OR, 3.9; 95% CI, 1.3-11.6), inner-city residence (OR, 3.5; 95% CI, 1.4-8.9), asthma in family member (OR, 3.5; 95% CI, 1.4-9.0), low (<5) position in sibship (OR, 3.6; 95% CI, 1.2-11), presence of smoker in home (OR, 3.7; 95% CI, 1.2-11.9), small household size (OR, 0.57; 95% CI, 0.35-0.93), and use of electricity as domestic fuel (OR, 0.34; 95% CI, 0.12-0.97). In the multivariate analysis sensitization to mites remained the strongest risk factor associated with the asthmatic group (OR, 10.4; 95% CI, 3.5-30.9). The other significant associations were inner-city residence (OR, 4.8; 95% CI, 1.5-5.2), sensitization to cockroach (OR, 4.9; 95% CI, 1.3-18.6), and position in sibship of less than 5 (OR, 6.3; 95% CI, 1.3-29.4).

CONCLUSION

Sensitization to dust mite and cockroach allergens, inner-city residence, and low position in sibship were independent risk factors for asthma in Ghanaian children.

Sensitization to common allergens and its association with allergic disorders at age 4 years: a whole population birth cohort study

BACKGROUND

Atopy is defined as the genetic propensity to develop immunoglobulin E antibodies in response to exposure to allergens and assessed by skin prick test responses to common allergens. Although it is generally agreed that atopy is an important risk factor for allergic diseases such as asthma, rhinitis, and eczema, the extent to which atopy accounts for these diseases is controversial.

OBJECTIVE

We aim to describe the prevalence of sensitization to common allergens and investigate the degree of association of atopy (as defined by positive skin prick test to 1 or more common allergens) to asthma, rhinitis, and eczema in a birth cohort at the age of 4 years.

METHODS

A birth cohort of 1456 children was recruited over a 14-month period (1989-1990). These children have been seen previously at 1 and 2 years of age. At 4 years, 1218 children were reviewed and an interview was administered or postal questionnaire was completed for the presence of allergic diseases (asthma, rhinitis, and eczema). Additionally, in 981 children, skin prick tests with a battery of 12 common allergens were performed. Allergens were house dust mite (Dermatophagoides pteronyssimus), grass pollen mix, cat, dog, Alternaria alternata, Cladosporium herbarum, cow's milk, hen's egg, soya, cod, wheat, and peanut. A mean wheal diameter of at least 3 mm greater than the negative control was taken as positive. This analysis is confined to the 981 (67% of the original population) who also had skin prick tests to the standard battery. chi(2) tests were used to test the univariate association between each allergic disease and positive skin test. Multiple logistic regression analysis was performed to obtain the adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for the independent effect of sensitization to each allergen on allergic disease, adjusting for the effect of sensitization to other allergens. To ascertain how much of allergic disease is attributable to atopy, we estimated the population-attributable risk. This was calculated with the formula: P(R - 1) where R is the OR for the allergic disease under consideration and P is the proportion of atopy in children with that disease.

RESULTS

Children who were skin prick-tested at 4 years were similar in most characteristics to the rest of the population, except that they had a higher prevalence of allergic disease. Allergic disorders (asthma, rhinitis, and eczema) were present in 276 (28.1%) of 981. One hundred ninety-two (19.6%) children were atopic (positive reaction to 1 or more allergens). Sensitization to inhalant allergens was relatively common (19.2%) as compared with food allergens (3.5%). House dust mite (11.9%), grass pollen (7.8%), and cat (5.8%) were the most common positive reactions. A test to the 4 most common allergens (house dust mite, grass pollen, cat, and A alternata) could detect 94% of the atopic children. Sensitization to the 4 most common allergens was strongly associated with the presence of allergic disorders. There was a graded effect with the potent allergens, such as house dust mite, having the greatest impact. For example, 50% of children sensitized to house dust mite had asthma as opposed to 44% sensitized to cat, 42% sensitized to grass pollen, and 32% sensitized to A alternata. Overall, 68.4% of children sensitized to house dust mite had asthma, eczema, and/or rhinitis. The respective figures for grass pollen, cat, and A alternata were 64.9%, 66.7%, and 57.4%. The proportion of children sensitized to cat was not higher in households with cat ownership (households with cats: 5.1% [19/374]; households without cats: 6.2% [36/580]; not significant [NS]). Similarly, no difference was seen in sensitization to dog in households with and without dogs (households with dogs: 1.8% [5/282]; households without dogs: 2.8% [19/673]; NS). Boys were atopic more often than girls at this age (male: 112 of 497 [22.5%] vs female: 80 of 484 [16.5%]; OR: 1.47, 95% CI: 1.07-2.02). Male preponderance was observed with most allergens, but this was statistically significant only for house dust mite (male: 75/497 [15.1%] vs female: 42/484 [8.7%]; OR: 1.87; CI: 1.25-2.79) and grass pollen (male: 51/497 [10.3%] vs female: 26/484 [5.4%]; OR: 2.01; CI: 1.23-3.29). An independent effect of allergen sensitization on asthma was observed only with house dust mite with an OR of 8.07 (CI: 4.60-14.14). The highest independent risk for rhinitis was sensitization to grass pollen (OR: 5.02; CI: 2.21-11.41), and for eczema, sensitization to peanut (OR: 4.65; CI: 1.02-21.34). The majority of children (98/192) were sensitized to >1 allergen. A graded effect was observed with the risk of allergic disease in the child increasing with the number of positive skin prick test reactions. This effect was consistent throughout the spectrum of allergic diseases (asthma, eczema, and rhinitis). (ABSTRACT TRUNCATED)

Effect of environmental manipulation in pregnancy and early life on respiratory symptoms and atopy during first year of life: a randomised trial

BACKGROUND

Asthma places huge demands on health-care services, and its prevalence is increasing. Reduction of exposure to environmental allergens could offer a realistic chance for primary prevention. Our aim was to ascertain whether or not living in a low-allergen environment reduces the risk of asthma and atopic diseases in infants.

METHODS

We assigned infants to four risk groups according to parental atopic status. We enrolled 291 high-risk couples (both parents atopic, no pets) into a prospective, prenatally randomised, cohort study, and allocated them to environmental manipulation, in which measures to reduce prenatal and postnatal allergen exposure were undertaken (active HRA) (n=145) or no intervention (control HRC) (n=146). Two further prospective groups were studied: 161 high-risk infants with pets in the home (HRP group) and 168 low-risk infants, whose parents were both non-atopic (LR group). The main outcome measures were signs and symptoms of atopic disease at 1 year of age.

FINDINGS

103 families dropped out or were lost to follow up. At age 1 year we followed-up 133 HRA, 118 HRC, 140 HRP, and 126 LR infants. Children in the HRA group were less likely to have respiratory symptoms during the first year of life than those in the HRC group. The most pronounced differences were in the relative risks for severe wheeze with shortness of breath (relative risk 0.44 [95% CI 0.20-1.00]), prescribed medication for the treatment of wheezy attacks (0.58 [0.36-0.95]), and wheezing after vigorous playing, crying, or exertion (0.18 [0.04-0.79]). Probability of respiratory symptoms in HRC and HRP infants was similar, whereas it was much lower in the LR than in the HRC group. Cat ownership was significantly associated with sensitisation to cats (24.6 [3.04-199.05]; p=0.003).

INTERPRETATION

Environmental manipulation reduces some respiratory symptoms in the first year of life in high-risk infants. Further follow up is needed, however, to ascertain whether living in a low-allergen environment reduces allergy and asthma in later life.

Pathophysiological mechanisms of asthma. Application of cell and molecular biology techniques

Asthma is a common increasing and relapsing disease that is associated with genetic and environmental factors such as respiratory viruses and allergens. It causes significant morbidity and mortality. The changes occurring in the airways consist of a chronic eosinophilic and lymphocytic inflammation, together with epithelial and structural remodeling and proliferation, and altered matrix proteins, which underlie airway wall narrowing and bronchial hyperresponsiveness (BHR). Several inflammatory mediators released from inflammatory cells such as histamine and cysteinyl-leukotrienes induce bronchoconstriction, mucus production, plasma exudation, and BHR. Increased expression of T-helper 2 (Th2)-derived cytokines such as interleukin-4 and 5 (IL-4, 5) have been observed in the airway mucosa, and these may cause IgE production and terminal differentiation of eosinophils. Chemoattractant cytokines (chemokines) such as eotaxin may be responsible for the chemoattraction of eosinophils to the airways. The initiating events are unclear but may be genetically determined and may be linked to the development of a Th2-skewed allergen-specific immunological memory. The use of molecular biology techniques on tissues obtained from asthmatics is increasing our understanding of the pathophysiology of asthma. With the application of functional genomics and the ability to transfer or delete genes, important pathways underlying the cause if asthma will be unraveled. The important outcome of this is that new preventive and curative treatments may ensue.

Childhood risk factors for atopy and the importance of early intervention

The increasing prevalence of atopic diseases, particularly atopy-associated asthma, has become a major challenge for allergists and public health authorities in many countries. The understanding of the natural history of the atopic march, including the determinants that are modifiable and might become candidates for preventive intervention, is still very limited. Information provided by cross-sectional studies can only generate hypotheses, which need to be supported by prospective, longitudinal, cohort studies. Ultimately, it will depend on the results of well-controlled intervention studies to identify which nutritional, environmental, or lifestyle-related factors should be considered for early intervention and might be useful to reverse the epidemiologic trend.

The bronchial epithelium in chronic and severe asthma

Although patients with severe, steroid-refractory asthma represent a minor proportion of the asthmatic population, they consume a disproportionate amount of healthcare costs and have a greatly impaired quality of life. They respond poorly to conventional anti-inflammatory therapy and frequently exhibit a component of fixed airflow obstruction that has been linked to airway wall remodeling. In addition to its classic barrier function, the bronchial epithelium responds to changes in the external environment by secreting cytoprotective molecules and mediators that signal to cells of the immune system. In asthma, the bronchial epithelium is stressed and damaged, with shedding of the columnar cells into the airway lumen. This damage and ensuing repair responses are proposed to orchestrate airway inflammation and remodeling via activation of myofibroblasts in the underlying lamina reticularis. This allows the two cell types to work as a trophic unit, propagating and amplifying the response at the cell surface into the submucosa. Because wound healing involves inflammation, repair, and remodeling processes, this review considers the evidence that exaggerated inflammation and remodeling of the airways arise as a consequence of abnormal injury and repair responses coordinated by the bronchial epithelium, highlighting, where possible, steroid-insensitive components.