Serial change of neutrophil extracellular traps in tracheal aspirate of patients with acute respiratory distress syndrome: report of three cases

BACKGROUND: Neutrophil extracellular traps (NETs) are fibrous structures released from activated neutrophils. NET formation has been reported to be associated with acute respiratory distress syndrome (ARDS). However, there are no reports dealing with serial changes of NET formation in tracheal aspirate of ARDS patients. CASE PRESENTATION: We report three cases of ARDS. Case 1 is a 69-year-old man with necrotizing fasciitis of the buttocks, case 2 is a 49-year-old woman with extensive burns (80% of total body surface), and case 3 is a 73-year-old woman with severe bacterial pneumonia. We found abundant expression of citrullinated histone H3 (Cit-H3) and the formation of NETs at the onset of ARDS in all cases. The amounts of Cit-H3 and NETs decreased with the amelioration of respiratory failure in cases 1 and 2. In case 2, the amounts of Cit-H3 and NETs increased with aggravation of infection and respiratory status. In case 3, the abundant expression of Cit-H3 and NETs persisted; the patient did not recover from ARDS and eventually died. Cit-H3 and NETs were found in tracheal aspirates even if the patients had no direct injury to the lung as in cases 1 and 2. CONCLUSIONS: In these three cases, the formation of NETs was observed in tracheal aspirate of patients with ARDS by either direct or indirect insults to the lung. The amount of NET formation changed dynamically over the clinical course of each patient.