[Cell types of respiratory epithelium: morphology, molecular biology and clinical significance]

The epithelium of the human lower airways is composed of several different cell types. In the proximal parts of the lower airways, the basal cell, the goblet cell, and the ciliated cell are the principal cell types. In the distal airways, the Clara cell and the ciliated cell are present. Serous and mucous cells are the secretory cell types of the glands which are found in the wall of the large airways. In the last few years, several cell- and molecular-biological characteristics of these cell types have been investigated and their importance to physiological and pathological processes has been clarified. The products of secretory cell types are essential for the mucociliary clearance and thus play an important part in defense. In many diseases, such as asthma or cystic fibrosis, the structure and function of these cells are altered in a characteristic way. Another defence mechanism is represented by the ciliated cells. Their function can be impaired by inborn or acquired diseases. Knowledge about cell differentiation and cell proliferation is important to understand both the physiological regeneration as well as pathological conditions, such as wound repair or neoplasms. Further, the development of gene-therapeutical approaches depends on the investigation of the molecular biology of the airway cells. It is the aim of this article to describe the morphology of the relevant cell types and molecular biological aspects of their function.