Neuroendocrine (NE) cells are found in small clusters, or neuroendocrine bodies (NEBs), at branch points along the airways and in lower numbers in the more distal regions of the lungs. The NE cells contain characteristic small, dense-cored granules that cluster at the basal pole of the cell and are secreted by exocytosis. These cells synthesize and secrete a number of peptides that exhibit growth factor-like activity.
Mash1 expression is required for NE cell commitment and differentiation. The earliest NE cells can be cytologically identified in humans at 8 weeks of gestation, when airway development is just beginning.