PATHOLOGICAL STUDIES OF NEUROENDOCRINE CELLS IN HUMAN EMBRYONIC AND FETAL LUNG: Light Microscopical, Immunohistochemical and Electron Microscopical Approaches

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Abstract
Quantitative light microscopical and immunohistochemical analyses, and electron microscopical studies including routine and uranaffin procedures were carried out on specimens of human embryonic and fetal lung to establish the ontogeny and function of neuroendocrine cells (NECs) and neuroepithelial bodies (NEBs). Light microscopically, NEC and NEB were first observed at 8 and 9 weeks of gestation, respectively. The average numbers of both per 100 bronchial trees rapidly increased from the late second trimester. Electron microscopically, a few dispersed dense granules with uranaffin positivity first appeared in immature glycogen-rich epithelial cells at 7 weeks, and differentiated NECs were observed at 8 weeks. The possibility that these glycogen-rich epithelial cells might be NEC precursors was therefore proposed. Immunohistochemically, bombesin and serotonin-immunoreactive (IR) NECs were first demonstrated at 8 and 9 weeks, respectively, and calcitonin-IR NECs first appeared at 20 weeks. The average numbers of these IR NECs and NEBs increased from the late second to third trimester. Adrenocorticotropic hormone (ACTH)-IR NECs and NEBs were found only in extrauterine fetal lungs. Bombesin was a cardinal peptide in fetal lungs, and was assumed to play a pulmonary maturation-promoting or trophic role.