Eosinophilic Airway Inflammation

What is Eosinophilic airway inflammation?

Eosinophilic airway inflammation is a type of immune‑mediated inflammation of the respiratory tract in which eosinophils—a specific white‑blood cell that normally helps fight parasites and modulates allergic responses—accumulate in the lining of the airways. When eosinophils become activated they release toxic proteins, cytokines, and growth factors that cause swelling, mucus production, and airway hyper‑responsiveness. This pattern of inflammation is most commonly linked to asthma, but it can appear in other respiratory conditions as well.

The term is used both descriptively (what the physician sees under a microscope or in a sputum test) and diagnostically (e.g., “eosinophilic asthma”). Identifying eosinophilic inflammation helps clinicians choose treatments that specifically target eosinophils, such as biologic therapies, and can predict response to inhaled steroids.

Common Causes

Several diseases and triggers can lead to eosinophilic airway inflammation. The most frequent are:

• Eosinophilic asthma – a phenotype of asthma characterized by high sputum or blood eosinophil counts.
• Allergic (atopic) asthma – driven by IgE‑mediated allergy to pollen, dust mites, animal dander, etc.
• Non‑allergic (intrinsic) eosinophilic asthma – eosinophilia without identifiable allergens.
• Churg‑Strauss Syndrome (Eosinophilic Granulomatosis with Polyangiitis) – a systemic vasculitis with prominent eosinophils.
• Allergic bronchopulmonary aspergillosis (ABPA) – hypersensitivity reaction to the fungus Aspergillus.
• Eosinophilic bronchitis – chronic cough with eosinophils in sputum but normal airflow.
• Respiratory viral infections (e.g., rhinovirus, influenza) that can transiently increase eosinophils in susceptible people.
• Occupational exposures – inhalation of chemicals, dust, or fumes that provoke eosinophilic responses (e.g., diacetyl, isocyanates).
• Medication‑induced eosinophilia – drugs such as non‑steroidal anti‑inflammatory drugs (NSAIDs), some antibiotics, or biologics can trigger airway eosinophilia.
• Parasitic infections – while rare in high‑income countries, helminths (e.g., Ascaris) can cause eosinophilic lung disease.

Associated Symptoms

Because eosinophilic inflammation narrows and irritates the bronchi, patients often experience a characteristic cluster of respiratory complaints:

• Wheezing or whistling sound on exhalation.
• Shortness of breath, especially during exertion or at night.
• Persistent dry cough that may worsen in the early morning.
• Chest tightness or “band‑like” pressure.
• Increased mucus production that can be thick and white or yellow‑green.
• Frequent need for rescue (short‑acting) inhalers.
• Symptoms that improve markedly with inhaled corticosteroids (a clue to eosinophilic involvement).
• In some cases—especially ABPA—fever, weight loss, or sinus symptoms may be present.

When to See a Doctor

Prompt medical evaluation is advised if you notice any of the following:

• Symptoms that persist > 2 weeks despite use of a short‑acting bronchodilator.
• Recurrent nighttime awakenings due to coughing or breathlessness.
• Worsening wheeze or cough after starting a new medication or after a respiratory infection.
• Need for increasing doses of rescue inhaler (more than twice a week).
• Any new “tightness” or pain in the chest that feels different from usual asthma symptoms.
• Unexplained weight loss, fever, or night sweats—possible signs of a systemic condition (e.g., EGPA or ABPA).

Early assessment can prevent irreversible airway remodeling and reduce the need for high‑dose steroids.

Diagnosis

Diagnosing eosinophilic airway inflammation involves a combination of clinical history, objective lung testing, and laboratory evaluation.

1. Clinical Evaluation

• Detailed symptom diary (trigger patterns, timing, medication response).
• Review of personal and family history of allergies, asthma, or autoimmune disease.

2. Pulmonary Function Tests (PFTs)

• Spirometry – measures forced expiratory volume (FEV₁) and can show reversible obstruction typical of asthma.
• Peak flow monitoring – helps track variability over days or weeks.
• In research settings, fractional exhaled nitric oxide (FeNO) is an inexpensive bedside test that correlates with eosinophilic inflammation.

3. Eosinophil Quantification

• Peripheral blood eosinophil count – a count ≥ 300 cells/µL often supports eosinophilic asthma.
• Sputum eosinophil differential – induced sputum examined under a microscope; ≥ 2‑3 % eosinophils is considered elevated.
• Bronchoscopy with airway brushing or lavage – reserved for ambiguous cases or suspected EGPA/ABPA.

4. Imaging

• Chest X‑ray is generally normal in isolated eosinophilic asthma but can reveal infiltrates in ABPA or EGPA.
• High‑resolution CT may show bronchial wall thickening, mucus plugging, or fleeting infiltrates.

5. Additional Tests (when indicated)

• Serum IgE levels & specific allergen skin‑prick tests (to detect atopic asthma).
• Serum precipitins or IgG to Aspergillus (ABPA screening).
• ANCA testing for eosinophilic granulomatosis with polyangiitis.

Treatment Options

Therapy is aimed at reducing eosinophil numbers, controlling airway hyper‑responsiveness, and preventing exacerbations.

1. Inhaled Corticosteroids (ICS)

First‑line anti‑inflammatory agents. They suppress eosinophil activation and are the most effective way to lower airway eosinophilia. Low‑to‑moderate doses are usually sufficient for mild disease; higher doses may be needed for severe cases.

2. Long‑Acting Beta‑Agonists (LABA) + ICS

Combination inhalers improve symptom control and allow lower steroid doses.

3. Leukotriene Receptor Antagonists (LTRAs)

Medications such as montelukast can reduce eosinophil recruitment and are especially useful in patients with concomitant allergic rhinitis.

4. Systemic Corticosteroids

Short bursts (e.g., prednisone 40‑60 mg for 5‑7 days) are used for acute exacerbations or when oral steroids are needed to control severe eosinophilic asthma.

5. Biologic Therapies Targeting Eosinophils

• Mepolizumab, Reslizumab, Benralizumab – monoclonal antibodies that block interleukin‑5 (IL‑5) or its receptor, dramatically lowering eosinophil counts.
• Dupilumab – blocks IL‑4/IL‑13 signaling, useful for patients with high eosinophils and comorbid atopic dermatitis or chronic rhinosinusitis.
• These agents are reserved for patients with ≥ 150 eosinophils/µL who have frequent exacerbations despite high‑dose ICS/LABA.

6. Treatment of Underlying Causes

• Allergen avoidance and immunotherapy for atopic triggers.
• Antifungal therapy (itraconazole) and oral steroids for ABPA.
• Immunosuppressive agents (e.g., cyclophosphamide) in EGPA when systemic vasculitis is present.
• Antiparasitic medication for helminth infections.

7. Home & Lifestyle Measures

• Use a peak flow meter daily to detect early loss of control.
• Maintain a clean indoor environment – dust‑mite covers, HEPA filters, and avoidance of tobacco smoke.
• Stay up‑to‑date on vaccinations (influenza, COVID‑19, pneumococcal) to reduce infection‑related exacerbations.
• Regular aerobic exercise improves lung capacity, but warm‑up before activity is essential for asthma patients.
• Monitor and limit exposure to occupational irritants; consider protective masks if avoidance is impossible.

Prevention Tips

While not all instances of eosinophilic airway inflammation can be prevented, the following strategies lower risk and help keep disease under control:

• Identify and avoid personal allergens – pollen, pet dander, mold, or dust mites.
• Adhere to controller medication regimens even when asymptomatic.
• Use a spacer** with inhalers** to improve drug delivery to the lower airways.
• Maintain a healthy weight – obesity is linked to increased eosinophilic inflammation and reduced steroid responsiveness.
• Limit exposure to air pollutants – avoid heavy traffic routes, use air purifiers indoors, and refrain from burning incense or candles.
• Practice good respiratory hygiene – hand washing, avoiding close contact with sick individuals, and wearing masks during viral outbreaks.
• Regularly review asthma action plans with your healthcare provider and update them when symptoms change.
• Stay hydrated – adequate fluid intake helps keep mucus thin and easier to clear.