<P> Chronic rejection explains long - term morbidity in most lung - transplant recipients, the median survival roughly 4.7 years, about half the span versus other major organ transplants . In histopathology the condition is bronchiolitis obliterans, which clinically presents as progressive airflow obstruction, often involving dyspnea and coughing, and the patient eventually succumbs to pulmonary insufficiency or secondary acute infection . </P> <P> Airflow obstruction not ascribable to other cause is labeled bronchiolitis obliterans syndrome (BOS), confirmed by a persistent drop--three or more weeks--in forced expiratory volume (FEV) by at least 20% . BOS is seen in over 50% of lung - transplant recipients by 5 years, and in over 80% by ten years . First noted is infiltration by lymphocytes, followed by epithelial cell injury, then inflammatory lesions and recruitment of fibroblasts and myofibroblasts, which proliferate and secrete proteins forming scar tissue . Generally thought unpredictable, BOS progression varies widely: lung function may suddenly fall but stabilize for years, or rapidly progress to death within a few months . Risk factors include prior acute rejection episodes, gastroesophageal reflux disease, acute infections, particular age groups, HLA mis - matching, lymphocytic bronchiolitis, and graft dysfunction (e.g., airway ischemia). </P> <P> One principal reason for transplant rejection is non-adherence to prescribed immunosuppressant regimens . This is particularly the case with adolescent recipients, with non-adherence rates near 50% in some instances . </P> <P> Diagnosis of acute rejection relies on clinical data--patient signs and symptoms but also calls on laboratory data such as blood or even tissue biopsy . The laboratory pathologist generally seeks three main histological signs: (1) infiltrating T cells, perhaps accompanied by infiltrating eosinophils, plasma cells, and neutrophils, particularly in telltale ratios, (2) structural compromise of tissue anatomy, varying by tissue type transplanted, and (3) injury to blood vessels . Tissue biopsy is restricted, however, by sampling limitations and risks / complications of the invasive procedure . Cellular magnetic resonance imaging (MRI) of immune cells radiolabeled in vivo might--similarly to Gene Expression Profiling (GEP)--offer noninvasive testing . </P>

Why does the immune system attack transplanted organs