What causes asthma
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Summary
10 papers analyzed
These studies suggest asthma is caused by a combination of environmental factors, genetic predispositions, and respiratory infections, leading to airway inflammation and hyperresponsiveness.
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Causes of Asthma: A Comprehensive Overview
Asthma is a complex and multifactorial disease characterized by chronic inflammation of the airways. The causes of asthma are diverse, involving a combination of environmental, genetic, immunological, and microbial factors. This article synthesizes the current understanding of the various causes of asthma, drawing on recent research findings.
Environmental Factors and Asthma
Allergens and Airway Hyperresponsiveness
Environmental allergens are a primary cause of asthma, particularly through IgE-mediated inhalant allergen exposures. These allergens induce airway inflammation and hyperresponsiveness (AHR), which are key features of asthma. The late asthmatic response (LAR) to allergens is associated with persistent airway inflammation and AHR, highlighting the role of allergens in the fundamental pathophysiology of asthma.
Air Pollution and Occupational Exposures
Exposure to air pollutants, such as diesel exhaust particles (DEP), has been linked to increased asthma prevalence and severity. DEPs can induce pulmonary oxidative stress, inflammation, and activation of bronchial epithelial receptors, contributing to asthma development. Occupational exposures to low-molecular-weight chemical sensitizers and textile dust can also cause asthma through mechanisms similar to allergen exposure .
Tobacco Smoke
Environmental exposure to tobacco smoke, particularly in children, facilitates the development of asthma. Personal smoking and environmental air pollution have inconsistent but generally small effects on asthma causation.
Immunological and Genetic Factors
Th2-Type Immune Response
Asthma is strongly associated with a polarized Th2-type T-cell response. This immune response involves various cells, including Th2 lymphocytes, IgE, mast cells, eosinophils, and cytokines, which contribute to airway inflammation and remodeling. Despite targeting Th2 cytokines in therapies, most treatments still rely on bronchodilators and corticosteroids .
Genetic Predisposition
Asthma has a significant genetic component, with various genes influencing susceptibility to the disease. Genetic factors interact with environmental exposures to shape the immune response and airway structure, contributing to asthma development .
Microbial Factors
Respiratory Infections
Respiratory viral infections, particularly rhinoviruses (RV) and respiratory syncytial virus (RSV), are major triggers of asthma exacerbations. These viruses can disrupt the airway epithelial barrier and create a Th2-biased inflammatory environment, increasing the risk of asthma development. RV is associated with atopic asthma, while RSV is linked to non-atopic asthma .
Microbiome and Infections
The role of the microbiome in asthma is increasingly recognized. Commensal bacteria in the gastrointestinal tract and certain infections may induce regulatory T cells (TR) that limit airway inflammation. In the absence of such infections, Th2 cells develop, promoting asthmatic inflammation.
Structural and Functional Airway Changes
Epithelial Barrier Dysfunction
Defective epithelial barrier function and impaired innate immune responses to viral infections provide a substrate for allergic sensitization and asthma persistence. These defects can lead to airway wall remodeling and increased susceptibility to environmental triggers, such as pollutants and allergens .
Airway Remodeling
Asthma involves structural changes in the airways, including epithelial, mesenchymal, vascular, and neurological events. These changes contribute to chronic inflammation and airway hyperresponsiveness, which are hallmarks of asthma .
Conclusion
Asthma is a multifactorial disease with diverse causes, including environmental allergens, air pollutants, respiratory infections, genetic predisposition, and structural airway changes. Understanding these factors is crucial for developing targeted prevention and treatment strategies. Ongoing research continues to uncover the complex interactions between these factors, paving the way for more personalized and effective approaches to managing asthma.
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