Pulmonary immune cells: villains and confederates.

Over the past ten years or so, we have been witnessing a slow but enduring change of mainstream research in respiratory medicine. From being widely dominated by studies of lung function and pulmonary physiology, research in respiratory medicine has begun to move into the complex field of cellular and molecular biology, in its effort to understand the basic mechanisms of disease. This progress has been due not only to advances in immunological and biological science but also to the introduction of the bronchoalveolar lavage (BAL) procedure which provides access to the various cell populations of the lower respiratory tract This issue of the Journal contains the first of a series of reviews planned to highlight the recent knowledge on pulmonary immune cells in health and disease [1]. Written by experts fully familiar with the modem laboratory techniques applied to the studies of immune cells, each of the ar1icles will be devoted to a specific cell type, including dendritic cells, macrophages, lymphocytes, neutrophils, eosinophils, mast cells, and platelets. Their beneficial role in host defence against invading pathogens, but also their harmful effects in chronic lung injury, will be addressed. The series will describe the origin. maturation and differentiation of the cells, surface antigens and receptor repertoires, enzyrre and mediator oontents, as well as the mechanisms of cellular recruit:rrent and activation. In addition to biological cell functions such as secretion of lipid mxliators and cytokines, migration, ~ and interactions with other cells, the potentially deleterious role in the pathogenesis of human diseases, will be summarized with an emphasis on respiratory disorders. Lastly, the potential implications for therapeutic strategies based on this new approach to lung diseases will be assessed. The article appearing in this issue deals with dendritic cells and Langerhans cells [1]. Langerhans cells are thought to be derived from dendritic cells. However, they differ from dendritic cells, since the latter are characterized by typical cytoplasmic ~lies called Birbeck granules, visible only by electron microscopy. Both cells are potent accessory cells or antigen-presenting cells and stimulate Iymphocyte proliferation, whereas alveolar macrophages function rather poorly in this respect [2] . An important lung disease, eosinophilic granuloma or histiocytosis X, has been renamed Langerhans cell granulomatosis, following the recognition that the offending cell is the LangedJans cell. Cltrrent concepts suggest that the disease results from an abnormal immune response in cigarette smokers, initiated and maintained by Langerhans cells [1].