Pulmonary immune cells in health and disease: dendritic cells and Langerhans' cells.

The activation of T-lymphocytes recognizing specific antigens is a crucial and early event in the development of an immune response, but T-lymphocytes cannot respond to antigens without help of a second cell type called accessory cells or antigen-presenting cells. Studies from several groups have indicated that pulmonary dendritic cells and Langerhans' cells, like their counterparts in other tissues, are potent accessory cells, and suggest that these cells may play an extremely important role in initiating lung immune responses. The purpose of this review is to summarize current information concerning pulmonary dendritic cells and Langerhans' cells, including their origin, distribution in the lung and functional capabilities. The possible role of these cells in certain lung diseases of immune origin will also be discussed.