Rationale: Eosinophilic Granulomatosis with Polyangiitis (eGPA), eosinophilic asthma and chronic rhinosinusitis with nasal polyps (CRSwNP) are airway diseases where eosinophils and interleukine-5 are involved in the pathogenesis. eGPA differs from the other diseases with respect to involvement of other organs. The investigators hypothesize that nasal microbiome dysbiosis with a central augmenting role for S. Aureus plays an important role in disease expression. The investigators expect that anti-interleukin-5 treatment with mepolizumab restores the changes of the nasal microbiome and immune responses to a healthy control phenotype. To study this, the nasal microbiome, the local and systemic immune response and the effect of mepolizumab treatment will be assessed.

See Brief summary.

Inclusion Criteria:

• 18 years of age

  • able to give informed consent
  • In CRSwNP group: availability of bilateral nasal polyps as diagnosed by endoscopy or CT scan
  • In Severe asthma group: clinical diagnosis of asthma with forced expiratory volume at one second(FEV1) <80% AND either FEV1 reversibility >12% initial or documented positive metacholine challenge (PC20 < 8 mg/ml)
  • In eGPA group: Fulfilling the 2022 ACR/EULAR criteria for eGPA (Wechsler et al., 2017)
  • In GPA group: fulfilling the American College of Rheumatology (ACR)/EULAR GPA criteria (Robson et al., 2022)
  • In healthy controls: absence of asthma symptoms, no bronchial hyperresponsiveness

Exclusion Criteria:

• unable to give informed consent
• Active smoking < (less than) 6 months from baseline visit
• Concomitant use of dupilumab within 6 months of baseline visit
• pregnant or breastfeeding woman
• in CRSwNP group: current use of asthma medication, eGPA
• in healthy controls: chronic use of local anti-inflammatory agents
• in healthy controls: use of immunosuppressive medication
• in healthy controls: use of antibiotics within the last month (before start study/screening/)

Patients with eosinophil driven inflammation for which mepolizumab might be considered for treatment

Fully anonymized data will be made available for other researchers