Proliferation and differentiation in mammalian airway epithelium

Abstract

The infrequency of mitotic figures led to dispute amongst early workers as to the occurrence of cell division in adult mammalian airway epithelium [30, 63, 83, 227]. It was not until 1951 that quantitative work in the respiratory tract began to concentrate on the distal (i.e. respiratory) portion of the lung (reviewed by BERTALANFFY (20, 21], KAUFFMAN [132], and MASSE et al. [159]). Studies of the lining epithelium of conducting airways soon followed [I I, 25, 26, 27, 32, 38, 148, 208, 230]. The present review summarizes the results of many studies of cell division and differentiation in conducting airway epithelium. I t is divided into three major sections: I) general principles and techniques used in assessment of cell kinetics; 2) normal proliferation and differentiation in conducting airways and 3) effects of irritants and carcinogens, mechanical trauma, drugs, infection and physiological factors on cell proliferation and differentiation. Proliferation and differentiation, which occur during airway development, are not discussed here: the interested reader is referred to the following papers and reviews [24, 47, 119, 129, 132, 207, 237]. At least eight epithelial cell types are recognised in the lining epithelium of conducting airways and three in the epithelium lining the alveoli (for reviews see [41, 116, 117, 118]). In man the tracheobronchial surface epithelium is pseudostratified, ciliated and columnar