NUMBER AND PROLIFERATION OF BASAL AND PARABASAL CELLS IN NORMAL HUMANAIRWAY EPITHELIUM

Two roles have been suggested for basal cells on the basis of studies performed with laboratory animals: (I) anchoring of the tracheobronchi al epithelium; and (2) being the epithelial stem cell. Parabasal cells located just above the basal cells have also been shown to contribute to cell renewal. However, a systematic study of the composition and p roliferation of basal and parabasal cells in normal human lungs is lac king. The aims of this study were to determine in normal human conduct ing-airway epithelium: (1) the number of basal and parabasal cells; an d (2) the contribution of basal and parabasal cells to the proliferati on fraction. Samples of histologically normal tissue, free of pulmonar y disease, were taken from seven lungs obtained by autopsy. Immunohist ochemical staining was performed with the primary antibody MIB-1 as a proliferation marker and the antikeratin antibody 34 beta E12 as a mar ker for basal and parabasal cells. In the largest conducting airways ( diameter greater than or equal to 4 mm), the percentages of basal and parabasal cells were 31% and 7%, respectively; the contribution to the proliferation compartment was 51% for basal and 33% for parabasal cel ls. In the smallest airways (diameter < 0.5 mm), 6% of epithelial cell s were basal cells, with a 30% contribution to the proliferation compa rtment, whereas parabasal cells were absent. The high fraction of basa l and parabasal cells contributing to the proliferation compartment of normal human conducting-airway epithelium supports the theory that ce lls at or near the basement membrane are likely to be progenitor cells .