Circulating Innate Lymphoid Cell Type 2 (ILC2) Levels and Asthma: a Case-control Study

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

Eligibility Criteria:
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