The present invention pertains to the monitoring and treatment of lung transplant recipients. In particular, the invention pertains to the use of biomarkers to predict or detect post-lung transplantation complications (e.g., organ rejection, acute organ rejection, organ injury, bronchiolitis obliterans, bronchiolitis obliterans syndrome, organizing pneumonia), fibroproliferative repair responses, interstitial lung diseases (e.g., idiopathic pulmonary fibrosis and other fibrotic lung diseases), and other immune-mediated lung diseases (e.g., graft versus host disease, scleroderma).