Allergen Management in Children with Type 2-High Asthma

Abstract

Children exposed to various indoor and outdoor allergens are placed at an increased risk of developing asthma in later life, with sensitization in these individuals being a strong predictor of disease morbidity. In addition, aeroallergen exposure influences asthma outcomes through an interplay with adverse determinants of health. The goal of this review is to provide an introductory overview of factors related to aeroallergen exposure in type 2-high childhood asthma. These include the relevance of exposure in asthma exacerbations and severity, and the evidence-base for avoidance and treatment for sensitization to these allergens. This review will focus on both indoor aeroallergens (house dust mite, pet, cockroach, mold, and rodent) and outdoor aeroallergens (pollens and molds). Treatment of aeroallergen sensitization in children with asthma includes avoidance and removal measures, although there is limited evidence of clinical benefit especially with single-strategy approaches. We will also address the interplay of aeroallergens and climate change, adverse social determinants, and the current COVID-19 pandemic, when we have seen a dramatic reduction in asthma exacerbations and emergency department visits among children. While there are many factors that are hypothesized to contribute to this reduction, among them is a reduced exposure to outdoor seasonal aeroallergens.

Keywords: COVID-19; aeroallergens; asthma; social determinants of health.

Figure 1

There are three aspects to the cellular and chemical pathology of asthma: the epithelial and subepithelial response the subsequent inflammatory process; and the impact on airway mucus and bronchoconstriction. When children with asthma inhale an aeroirritant, there is a complex interplay of cells and chemical that is poorly understood. The main chemical players are called “alarmins”, and these link with cells such as Antigen-Presenting Cells and Dendritic Cells. These drive a shift in the types of T-cells that a person has. In most people with asthma there is an imbalance such that the undifferentiated T-helper cell (Th-0) is more likely to become a Th2, rather than Th1, cell. When this happens, people are said to have “Type 2-high” asthma; this is the usual phenotype in children. There are two main asthma endotypes in children with Type 2-high asthma - the eosinophilic pathway, and the IgE-mediated pathway. The key chemicals that drive these pathways include Interleukin 4/13 and Interleukin-5. Children exhibit these pathways and endotypes to varying degrees. There are other aspects of the pathogenesis, such as Th-17, which promote non-Type 2 inflammation. The consistent driver in children with Type 2-high asthma is that avoidance of aeroirritants in the first place significantly reduces the inflammatory load.