[Pathology of lung transplantation and molecular aspects of pathogenesis]

Lung transplantation has become an established therapy for patients with a variety of end stage pulmonary diseases during the last twenty years. Many complications can affect the lung after transplantation, e.g. preservation related injury, mechanical complications of surgery, acute or chronic (obliterative bronchiolitis) rejection, infection, drug toxicity, recurrent disease, de novo disease, lymphoproliferative disorder. The regulation of tissue inflammation and repair mechanisms involving components of the immune systems depends on a number of cell-cell interactions. Today, our understanding of this pathogenetic and functional network is still at the beginning. The numbers of molecules and factors involved are still increasing. Technical progress has introduced a lot of new molecular techniques (e.g. PCR, cDNA Microarray etc.) for analysis of transplant reaction. Nevertheless assessment of lung allografts is usually by transbronchial biopsy and less commonly by thoracoscopic or open lung biopsy. A minimum of five fragments of alveolated lung parenchyma is required. Biopsies are examined by routine haematoxylin and eosin stain, connective tissue or elastic stains and further special stains, immunohistochemistry and molecular techniques will be performed if required. In examining biopsies from lung allografts three critical points to assess are: a. the presence or absence of acute rejection or b. chronic rejection (obliterative bronchiolitis), and c. the identification of infection. Interpretation of the histology requires knowledge of the clinical and microbiological results. New molecular techniques could help to elucidate the pathogenesis of transplant reaction and provide new insights to facilitate the clinical diagnostics of allograft pathology.