The main objectives of the study are

1. to study the different T cell subtypes (Th1, Th2, Th17 and Treg) in the lower airways of healthy subjects and clinically different asthma patients, based on a non-invasive procedure of sputum induction. Patients will be different in function of age, in relation to the trigger (eg aspirin, without or with association with polyposis), without or with underlying atopic sensitization or different in the type of underlying inflammation (eosinophilic vs neutrophilic). This T cell pattern will become the basis of molecular phenotyping in the patients.
2. to study the usefulness of asthma molecular phenotyping (by following the balance between the inflammatory markers on the one hand and the regulatory markers on the other hand) in asthma guidance (longitudinally).

The final goal of this project is then to develop a sputum non-invasive biomarker array that can be used to distinguish the different inflammatory asthma phenotypes and that can predict steroid resistance and/or sensitivity to other anti-inflammatory medication, using a non-invasive technique that can be used also at young age and repetitively.

Inclusion Criteria:

• asthma diagnosis

Exclusion Criteria:

• viral/bacterial/fungal infection with fever (<1 month )
• other airway diseases (CF, ciliar dyskinesia, bronchiectasis)
• asthma exacerbation (<3 months)

330 asthmatics (300 adults, 30 children) will be recruited from the outpatient clinic of the university hospital of Leuven. 115 healthy subjects (100 adults, 15 children) will be recruited among students and co-workers from the KULeuven and UZ Leuven.