• PNNs phagocytic index [ Time Frame: 24 hours after BAL ]
  This index relates the ability of the PNNs to produce neutrophil extracellular traps (NETs). The release of NETs was quantified by measuring fluorescence with a microplate fluorescence reader (Varioskan, ThermoFisher Scientific, USA).
• Efferocytosis index [ Time Frame: 24 hours after BAL ]
  The efferocytosis index was determined on 300 cells as the percentage of Human monocyte-derived macrophages (HMDMs) containing at least one ingested apoptotic neutrophil.
• Increase of PNNs phagocytic index with HMGB1 activator [ Time Frame: 24 hours after BAL ]
  PNNs phagocytic index is measured after incubation with an anti-HMGB1 neutralising antibody
• Increase of Efferocytosis index metformin [ Time Frame: 24 hours after BAL ]
  efferocytosis index was determined after incubation with an AMP-activated protein kinase (AMPK) activator (metformin)

Firstly, the study assesses the effect of bronchoalveolar lavage fluid (BAL) from patients in (acute respiratory distress syndrome (ARDS) on the life span of PNNs and on the phagocytosis of apoptotic cells by macrophages and polynuclear neutrophil (PNN).

Then, the effect of an antibody directed against "high-mobility group box 1" protein (HMGB1) and the effect of metformin on efferocytosis are studied.

ARDS (acute respiratory distress syndrome) is a syndrome that causes significant mortality and morbidity. This syndrome is characterized by an alveolitis with polynuclear neutrophil (PNN). PNNs play an important role in the persistence and in injuries induced by ARDS. Several animal studies have shown that lesional edema can be increased by two important mechanisms: the increase in the lifespan of PNNs in the lung and the decrease in the phagocytosis capacities of apoptotic cells (efferocytosis) by macrophages and PNNs.

However, confirmation of these data in humans does not exist, and knowledge of the mechanisms that may increase lung damage during ARDS will limit it and thus reduce the mechanical ventilation time of these patients as well as the mortality associated with ARDS.

" high-mobility group box 1 " (HMGB1) protein may be involved in reducing efferocytosis capacity. Similarly, activation of AMP-activated protein kinase (AMPk) could restore the clearance capacity of apoptotic cells in macrophages and PNNs.

• ARDS Group : Inpatients hospitalized in medical intensive care with an ARDS defined according to the Berlin criteria and requiring an BAL(for diagnostic purpose in suspicion of pneumopathy acquired under mechanical ventilation).
• Control group : The control population is made up with patients with a BAL considered normal (endoscopy patients from the pneumology department). The normality of the BAL is defined by a normocellular wash with cellularity: < 150,000 to 200,000 cells/mL Cell composition (formula): macrophages: 80-90%, lymphocytes 5 to 10% (< 20%), neutrophils: < 5%, eosinophils: < 2%.

• ARDS group
  Inpatients hospitalized in medical intensive care with a table of ARDS defined according to the Berlin criteria and requiring an BAL for a diagnostic purpose under a suspicion of pneumopathy acquired under mechanical ventilation.
  Intervention: Procedure: Bronchoalveolar lavage
• Control group
  The control group will be made up of patients with an BAL considered normal (endoscopy patients from the pneumology department). The normality of the BAL is defined by a normocellular wash with cellularity: < 150,000 to 200,000 cells/mL Cell composition (formula): macrophages: 80-90%, lymphocytes 5 to 10% (< 20%), neutrophils: < 5%, eosinophils: < 2%.
  Intervention: Procedure: Bronchoalveolar lavage

Inclusion Criteria:

• ARDS Group : Inpatients hospitalized in medical intensive care with an ARDS defined according to the Berlin criteria and requiring an BAL(for diagnostic purpose in suspicion of pneumopathy acquired under mechanical ventilation).
• Control group : The control population is made up with patients with a BAL considered normal (endoscopy patients from the pneumology department). The normality of the BAL is defined by a normocellular wash with cellularity: < 150,000 to 200,000 cells/mL Cell composition (formula): macrophages: 80-90%, lymphocytes 5 to 10% (< 20%), neutrophils: < 5%, eosinophils: < 2%.

Exclusion Criteria:

• Age < 18 years;
• Pregnant women ;
• Persons deprived of their liberty by judicial or administrative decision;
• Persons legally incapable;
• Persons not affiliated to a social security system;
• Previously immunocompromised patients (HIV infection, hematopathy, organ transplantation, immunosuppression);
• Patients who do not require a lung sample.