The primary objective of this study is to demonstrate differences in ILC2 blood levels between asthma patients and control patients.

The secondary objectives of this study are:

To show that ILC2 levels differ between asthma patients with a "TH2" (helper T cell type 2) profile and asthma patients with a "non-TH2" profile. A TH2 profile is defined as (for a given patient):

• circulating eosinophils > 500 mm^3 at least once during the year AND
• positive allergy skin or specific IgE (Immunoglobulin E) test AND
• induced sputum eosinophil level >3% of leukocytes AND
• exhaled nitric oxide > 25 ppb.

To study the variation in ILC2 levels over time among asthma patients who obtained a good level of control compared to other patients. A good level of control is defined as:

• no exacerbations during 6 months of followup (an exacerbation is defined as the un-planned need for care that modifies the patient's prescription for >48h)
• FEV1 (forced expiratory volume in 1 second) value current / FEV1 best value > 0.8
• symptom levels correspond to an ACQ (Asthma Control Questionnaire) questionnaire score of < 0.75 over the last 7 days

Inclusion Criteria for Cases:

• The subject has given his/her informed consent and signed the consent form
• The subject is affiliated with or beneficiary of a medical insurance system
• The subject has had asthma for over a year
• The following are present in the patient's medical file: (i) a positive methacholine test (PC20 < 16 mg/ml) OR (ii) reversibility > 200 ml and 12% of the FEV1 after inhaling 400 µg or less of a short acting bronchodilator.
• Treatment with >= 1000 µg inhaled beclometasone equivalents

Exclusion Criteria for Cases:

• The subject is pregnant
• The subject is breastfeeding
• The subject is participating in another interventional study
• The subject has participated in another study in the 3 months preceding inclusion
• The subject is in an exclusion period determined by a previous study
• The subject is under judicial protection or is an adult under any kind of guardianship
• The subject refuses to sign the consent
• It is impossible to correctly inform the subject
• The subject cannot fluently read French
• Chronic respiratory disease present, known or suspected (other than asthma)
• Treated with Montelukast

Inclusion Criteria for Controls:

• The subject has given his/her informed consent and signed the consent form
• The subject is affiliated with or beneficiary of a medical insurance system

Exclusion Criteria for Controls:

• The subject is pregnant
• The subject is breastfeeding
• The subject is participating in another interventional study
• The subject has participated in another study in the 3 months preceding inclusion
• The subject is in an exclusion period determined by a previous study
• The subject is under judicial protection or is an adult under any kind of guardianship
• The subject refuses to sign the consent
• It is impossible to correctly inform the subject
• The subject cannot fluently read French
• Any kind of bronchial problem
• Smokers
• Chronic respiratory disease present, known or suspected
• Treated with Montelukast

This case-control study compares cases (asthma patients) with healthy control subjects. Patients and controls are matched by sex and age (+- 5 years).