NUMBER AND PROLIFERATION OF NEUROENDOCRINE CELLS IN NORMAL HUMAN AIRWAY EPITHELIUM

Pulmonary neuroendocrine cells (PNECs) are ubiquitous in human adult a irway epithelium, and are implicated in pulmonary disease as PNEC hype rplasia has been described in a great number of different pulmonary le sions. The purpose of this study was to determine the baseline quantit y and proliferative fraction of adult PNECs in the conducting airway e pithelium of normal lungs. Autopsy was performed within 6 h of death o n 250 subjects. in 9 of 250 cases without pulmonary disease, seven seq uential samples were taken from trachea down to respiratory bronchiole s, fixed in formalin, and embedded in paraffin. After microwave pretre atment in citrate buffer, sequential immunohistochemical staining was carried out, using MIB-1 (antibody directed against recombinant parts of the Ki-67 antigen) as marker for the proliferation fraction and chr omogranin-A (CgA) for the identification of PN ECs. Quantification of all epithelial cells of the conducting airways, MIB-1, and CgA immunor eactive cells, and length of basement membrane was interactively perfo rmed using image analysis. The results show that microwave treatment s ignificantly enhances the sensitivity of CgA without loss of specifici ty. In total, 326,500 epithelial cells and 105 cm of basement membrane (BM) length were counted (3,101 cells/cm BM). The proliferation fract ion of all epithelial cells was 0.76 +/- 0.53% (mean +/- SD). No mitos is was seen. The mean quantity of PNECs was 0.41 +/- 0.17% of all epit helial cells (12.5 cells/cm BM). Many dendritic PNEC processes paralle l to the basement membrane could be appreciated between adjacent epith elial cells. No difference in the number of PNECs was found between la rge and small conducting airways. PNECs were not observed in the alveo li. Only 13 PNECs were immunoreactive for MIB-1; the proliferative fra ction of PNECs was 1 to 2%. In histologically normal adult human condu cting airway epithelium, the average overall proliferation fraction is 0.76%. The proliferation fraction of PNECs is equal to the overall pr oliferative fraction. The fraction of PNECs is 0.47%, using anti-CgA a ntiserum after microwave pretreatment of slides, 12 times more than pr eviously reported. Many dendritic neuroendocrine cell processes were s een between non-neuroendocrine epithelial cells adjacent to the baseme nt membrane. The widely held belief that neuroendocrine cells are of l ittle importance in the adult lung is contradicted by the relative hig h density of PNECs and its cytoplasmic processors.