Eosinophilic asthma is a type of asthma characterized by increased levels of eosinophils, a white blood cell, in the airways. This condition leads to inflammation and narrowing of the bronchial tubes, contributing to asthma symptoms. Understanding the factors that contribute to this inflammation is central to effective management.
Understanding Eosinophils and Their Role
Eosinophils are immune cells produced in the bone marrow, residing in various tissues, particularly in the respiratory and digestive systems. They function as part of the body’s defense system, containing granules filled with proteins and enzymes that destroy pathogens.
In eosinophilic asthma, these protective cells become overactive or accumulate in high numbers within the airways. This leads to persistent inflammation, contributing to asthma symptoms like wheezing, coughing, and shortness of breath. Elevated eosinophils are a distinguishing feature of this asthma subtype.
Specific Triggers and Pathways in Eosinophilic Asthma
Several factors can drive eosinophil-mediated inflammation in eosinophilic asthma. Some cases are linked to external exposures, while others involve internal immune system dysregulation. Identifying these influences helps guide treatment.
Environmental allergens like pollen, dust mites, pet dander, and mold can contribute to eosinophil-driven inflammation. These trigger an immune response that recruits and activates eosinophils in the airways. This allergic reaction leads to the release of inflammatory substances that further draw eosinophils to the site. Avoiding identified allergens can reduce this inflammatory burden.
Respiratory infections, viral or bacterial, can also initiate or worsen eosinophilic inflammation. These infections provoke an immune response that increases eosinophil activity. Environmental irritants such as air pollutants, tobacco smoke, or strong fumes may also contribute to airway inflammation.
A significant aspect involves underlying immune dysregulation, often referred to as Type 2 inflammation. This pathway is driven by specific signaling proteins, called cytokines, produced by immune cells. Interleukin-5 (IL-5), Interleukin-4 (IL-4), and Interleukin-13 (IL-13) are prominent among these cytokines, playing a central role in the production, maturation, and activation of eosinophils. This internal process can lead to elevated eosinophil levels and airway inflammation even in the absence of clear external triggers, which is characteristic of non-allergic eosinophilic asthma.
Identifying Eosinophilic Asthma Triggers
Healthcare professionals use several methods to identify inflammatory pathways or triggers in eosinophilic asthma. This comprehensive evaluation helps determine the most effective management strategy.
Blood tests are a common initial step, looking for elevated eosinophil counts, typically at least 150 cells/µL, though often over 300 cells/µL. Sputum eosinophil counts, obtained from a mucus sample, are considered a comprehensive measure of airway eosinophilic inflammation, with more than 2-3% of cells being eosinophilic. A fractional exhaled nitric oxide (FeNO) test measures nitric oxide in exhaled breath, with higher levels indicating eosinophilic inflammation.
Allergy testing, including skin prick tests or blood tests that measure immunoglobulin E (IgE) levels, can help identify environmental allergens. While not all eosinophilic asthma is allergic, identifying an allergic component can inform treatment strategies. A thorough medical history, including symptom patterns and potential environmental exposures, is also essential for pinpointing potential triggers and understanding the individual’s condition.
Strategies for Managing Eosinophilic Asthma
Effective management involves identifying and addressing triggers and underlying inflammatory pathways. Avoiding or minimizing exposure to identified environmental triggers can help reduce symptom frequency and severity. This might involve reducing allergens in the home or taking precautions during periods of high outdoor allergen counts.
Treatment often involves medications that target the eosinophilic inflammatory pathway to reduce airway inflammation. Inhaled corticosteroids are commonly used. For more severe forms, oral corticosteroids may be prescribed.
Newer targeted therapies, known as biologics, are available for severe eosinophilic asthma. These medications block specific cytokines, such as IL-5, or their receptors, reducing eosinophil activity. Examples include mepolizumab, reslizumab, and benralizumab. Management typically combines trigger avoidance and these targeted medications.