Chronic allograft rejection (obliterative bronchiolitis)

Lung and heart-lung transplantation are currently recognized as effective treatment for selected patients with end-stage lung or heart-lung disease. Although the survival rates have improved in recent years, long-term survival is still hampered by the development of chronic rejection. Histologically chronic rejection is manifested by obliterative bronchiolitis (OB), a process that leads to airways obstruction, with a gradual decline in pulmonary function tests. Extensive research efforts have attempted to unravel the pathophysiology of OB and identify key cytokines and growth factors involved in the process. Since the histological diagnosis of chronic rejection remains difficult, a clinical grading system has been proposed, determined as bronchiolitis obliterans syndrome (BOS), divided into four and, more recently, five categories, depending on the severity of airflow obstruction. This paper reviews the current knowledge of chronic rejection after heart-lung and lung transplantation.