[Pulmonary dendritic cells]

The dendritic cells were initially described in lymphoid organs and have been recently shown in the normal human lung at the level of the bronchioles, preferentially in the peribronchiolar connective tissue and in the alveolar parenchyma. Langerhans cells, which constitute a sub-population amongst the dendritic cells are equally present, but virtually exclusively limited to the bronchiolar epithelium. The pulmonary Langerhans cells probably derive from dendritic cells as in the skin. The number and state of differentiation of pulmonary dendritic cells vary as a function of the epithelial microenvironment which seems necessary in the differentiation of dendritic cells into Langerhans cells. Langerhans cells are frequently seen in zones of alveolar hyperplasia and/or alveolar metaplasia induced by tobacco or by inflammatory lesions. Dendritic cells and Langerhans cells have a potent capacity for presenting an antigen to lymphocytes. Their presence in the normal lung and their differentiation in the course of certain pathological pulmonary processes strongly suggest that they have a significant role in the pulmonary immune response as well as in the pathogenesis of certain diseases.