⁃ Healthy subjects

• Written informed consent indicating that they understand the purpose and procedures required for the study and are willing to participate in the study.

• Age higher than 18 years.

• No prior history of any chronic respiratory disease including asthma.

• No prior history of allergy, i.e. allergic rhinitis, allergic conjunctivitis, hay fever, eczema.

• No clinically significant abnormalities as determined by medical history, measurement of vital signs, physical examination, hematologic assessments and ECG at visit 1.

• Normal lung function with FEV1 \> 90%.

⁃ Non-severe asthmatics subjects

• • Written informed consent indicating that they understand the purpose and procedures required for the study and are willing to participate in the study.

• Age higher than 18 years.

• Diagnosis of non-severe asthma according to the Global Initiative for Asthma (GINA), i.e. GINA steps 1, 2 or 3 (18).

• Documented post-bronchodilator reversibility of at least 12% and at least 200 mL in FEV1 within 12 months before enrolment, or PC20 methacholine \< 16 mg/mL documented within 12 months prior to screening.

• Documented blood eosinophils ≥300 cells per μL within 12 months or blood eosinophils ≥150 cells per μL at visit 1.

⁃ Severe asthmatics subjects

• • Written inform consent indicating that they understand the purpose and procedures required for the study and are willing to participate in the study.

• Age higher than 18 years.

• Diagnosis of severe asthma according to the American Thoracic Society (ATS)/European Respiratory Society (ERS) task force (19).

• Documented post-bronchodilator reversibility of at least 12% and at least 200 mL in FEV1 within 12 months before enrolment.

• Documented blood eosinophils ≥300 cells per μL within 12 months or blood eosinophils ≥150 cells per μL at visit 1.