Asthma is a chronic respiratory condition characterized by inflammation and narrowing of the airways, making breathing difficult. Eosinophilic asthma is a specific subtype driven by a particular white blood cell, identified by elevated levels of these immune cells in the airways.
The Role of Eosinophils in Asthma
Eosinophils are white blood cells that defend against parasitic infections and are involved in allergic reactions. In eosinophilic asthma, these cells become overactive and accumulate in the respiratory tract, including the sinuses and lower airways. This triggers inflammatory responses within the airways.
Activated eosinophils release inflammatory mediators and toxic proteins, such as major basic protein and eosinophil cationic protein, which damage airway tissues. This leads to inflammation, increased mucus production, and bronchial spasms, contributing to airway narrowing and obstruction. Unlike other forms of asthma often triggered by specific allergens, eosinophilic asthma may not be associated with allergies and involves a Type 2 inflammatory pathway.
Identifying Eosinophilic Asthma
Identifying eosinophilic asthma involves evaluating specific symptoms and conducting specialized tests.
Symptoms
Individuals with eosinophilic asthma commonly experience persistent symptoms such as wheezing, coughing, shortness of breath, and chest tightness. They may also present with chronic rhinosinusitis, nasal polyps, and a reduced sense of smell, indicating broader airway involvement. These symptoms often persist despite standard asthma treatments, prompting further investigation.
Diagnostic Tests
Diagnosis begins with blood tests to measure eosinophil counts. An elevated blood eosinophil count, often at least 150 cells/μL and commonly exceeding 300 cells/μL, can suggest eosinophilic asthma. However, a high blood eosinophil count alone is not definitive, as other conditions can also cause elevated levels, requiring clinical context for interpretation. Sputum analysis, where an eosinophil count of 2-3% or more of total cells strongly indicates eosinophilic airway inflammation.
Further Diagnostic Methods
Measuring fractional exhaled nitric oxide (FeNO) may also be elevated. Lung function tests, such as spirometry, typically show airflow obstruction consistent with asthma. A bronchial biopsy may be performed to assess eosinophil infiltration in lung tissues. A comprehensive diagnosis relies on a combination of these tests, along with the patient’s medical history and response to initial treatments.
Treatment Approaches
Managing eosinophilic asthma requires specific strategies beyond conventional asthma treatments, which may not fully control the underlying inflammation.
Initial Management
While standard therapies like inhaled corticosteroids are part of the treatment regimen, they might not be sufficient, particularly in severe cases. Oral corticosteroids can be used for acute exacerbations but carry risks of significant side effects with prolonged use. The focus for long-term management often shifts to advanced therapies.
IL-5 Targeting Biologics
Biologic medications, which are monoclonal antibodies designed to target specific components of the immune system, are a significant development. These biologics work by interfering with the pathways that drive eosinophilic inflammation. For instance, mepolizumab (Nucala) and reslizumab (Cinqair) specifically bind to interleukin-5 (IL-5), a cytokine that promotes the growth and activation of eosinophils. Benralizumab (Fasenra) targets the IL-5 receptor on eosinophils, leading to their depletion.
Other Biologics
Other biologics address different inflammatory pathways involved in Type 2 inflammation. Dupilumab (Dupixent) blocks the IL-4 receptor alpha subunit, thereby inhibiting both IL-4 and IL-13, two cytokines that contribute to airway inflammation. Tezepelumab (Tezspire) targets thymic stromal lymphopoietin (TSLP), an upstream mediator that initiates a broad inflammatory response in the airways. These targeted therapies can significantly reduce asthma exacerbations, improve lung function, and decrease the reliance on oral corticosteroids, offering improved disease control and quality of life for individuals with eosinophilic asthma.