Complex Interactions of Pollutant and Allergen Exposures and Their Impact on People With Asthma

Abstract

Pediatric asthma has many causes and can manifest differently in different children and at different times. Understanding the many factors related to the development and exacerbation of asthma is complicated by the complexity of the many environmental exposures related to asthma development and morbidity. Furthermore, the same environmental exposures that may cause increased symptoms at 1 point in time may be protective when the exposure occurs earlier or at high enough levels. We know that environmental exposures such as allergens, irritants, and pollutants are quite complex in their composition; further examination of this complexity may improve our understanding of this complex and highly prevalent disease. Pediatrics 2009;123:S160-S167 I N THE PAST 20 years, we have begun to understand that airway inflammation in asthma arises from maladaptation to environmental stresses. In studying this process, we have tended to focus on one mechanism or another (eg, immunoglobulin E [IgE]-mediated responses to biological materials or oxidative stress resulting from ozone or particulates) and have found evidence that each is important. Patients encounter these environmental stresses simultaneously, however, and this simultaneous exposure may enhance responses (ie, adjuvant or priming) or may decrease responses to one of the stressors. We have begun to address the issue of complex responses to simultaneous exposure to other bioactive materials in the hygiene hypothesis. 1,2 Originally, this hypothesis proposed that the increased prevalence of allergic diseases was related to a population shift in immune responsiveness because infectious illnesses were less prevalent. More recently, researchers found that children had less asthma and allergic disease when they were exposed early in life to endotoxin from Gram-negative bacteria, 2 a finding that seems to confirm the hygiene hypothesis. This finding, however, could also be an example of effect modification (ie, simultaneous exposure to endotoxin in airborne particulates decreased IgE-mediated sensitization to allergens). ENVIRONMENTAL ALLERGENS ARE CARRIED ON PARTICLESOur understanding of environmental allergen exposure depends on continually developing technology that allows us to measure levels of allergenic proteins in the environment. Technological advances have made it possible to test the hypotheses that environmental allergen exposure is related to sensitization, asthma prevalence and severity, and asthma incidence rates. In addition, asthma prevalence and severity have clear dose-response relationships to allergen exposure. Indoor allergen levels measured both in settled household dust and in indoor air are more clearly related to asthma than are outdoor allergen levels 3 ; therefore, many of the data supporting a discussion of interactions between allergens and pollutants refer to indoor allergen exposure. An important corollary of those studies is the demonstration that allergens carried on airborne particles have clearly defined characteristics that are rel...

A rapid assessment of the impact of hazard reduction burning around Sydney, May 2016

“…Eggleston (2009) concluded that "the same environmental exposures that may cause increased symptoms at one point in time may be protective when the exposure occurs earlier or at high enough levels".…”

State of Childhood Asthma and Future Directions Conference: Overview and Commentary

“…The risks of engaging in outdoor activities or living near heavily polluted roadways are associated with the development of asthma in childhood and subsequently diminished lung function. In addition, as Eggleston 16 notes, children with asthma come into contact with bioactive pollutants and allergens simultaneously. He indicates that many of these small-molecule pollutants likely serve as adjuvants to magnify the immunoglobulin E-mediated inflammation that is characteristic of asthma in children.…”

“…For example, asthma morbidity can negatively influence the psychosocial environment of both the child with asthma and the family, and this can decrease the effectiveness of the child's asthma management, leading to increased asthma morbidity. 17 As Eggleston 16 points outs, the effects of allergen exposures can be accentuated by environmental pollution or viral infections. Additional complexity results from the fact that not all of these factors interact in the same way for all children.…”

Short-term Associations between Ambient Air Pollutants and Pediatric Asthma Emergency Department Visits

“…To help advance understanding of the relationships between ambient air pollutant concentrations and asthma exacerbations in children, further characterization of the dose-response and pollutant lag effects are needed, as are investigations of pollutant species beyond the commonly measured urban air pollutants (3,7). Further investigation of pollutant mixtures and effect modification may also provide insights (8,9); for example, there have been reports of stronger pollution effects during the warm season (10-15) even though pediatric asthma rates peak during the cold season (16). To lessen concerns about uncontrolled confounding, aggressive control for variables, such as meteorology and seasonal asthma trends, is required.…”

“…Our study takes advantage of daily measurements of components of particulate matter less than 2.5 mm in aerodynamic diameter (PM 2.5 ), a resource not typically available to investigators, which enables us to distinguish among the various compounds that comprise PM 2.5 . We investigated effect modification by season and potential confounding by ambient pollen concentrations and upper respiratory infections, because it is well known that these factors can trigger asthma exacerbations (9). The extent to which ambient pollen concentrations and circulating respiratory viruses confound associations between air pollutant concentrations and asthma exacerbations depends on the nature of the associations between short-term…”