Background: Microvesicles (MV) play important roles in mediating intra-alveolar inflammation during acute lung injury. We investigated the MV profiles within bronchoalveolar lavage fluid (BALF) in patients undergoing lung transplantation and assessed relationship to the development of primary graft dysfunction (PGD).

Methods: Lung transplant patients underwent bronchoscopy after completion of surgery and BALF samples (n=31) were analysed by flow cytometry for MVs derived from leucocytes (CD45+), neutrophils (CD66b+/CD11b+), monocytes (CD45+/CD14+), alveolar macrophages (CD206+/CD71+), platelets (CD31+/42b+) and epithelial (EpCAM+/T1α+) cells. MV numbers were correlated to clinical outcomes including hypoxia and development of PGD.

Results: Various MV subpopulations were identified in BALF. Neutrophil-derived MVs were the largest population (10,548 (3,925-51,529)) compared to leucocyte MVs (9797 (4763-53444)), monocyte MVs (438 (196-25,627)), alveolar macrophage MVs (755 (343-6054) and platelets MVs (564 (286-953)) (MVs/µL, median (IQR)). Patients with PaO2/FiO2 (P/F) ratio ≤ 200mmHg at 72 hours had significantly higher levels of BALF neutrophil MVs than those with P/F ratio > 200mmHg (p=0.001). Patients who developed PGD also had significantly higher BALF neutrophil MVs than those who did not (p=0.03).

Conclusions: We have undertaken a comprehensive evaluation of MVs within BALF of lung transplant recipients and demonstrated an association of BALF neutrophil MV numbers and PGD. Our data may suggest BALF neutrophil MVs as a potential, clinically relevant biomarker for PGD. Moreover, these MV may also have a pathogenic/inflammatory role in development of PGD