ABSTRACT
Pulmonary endocrine cells (PECs) are part of the diffuse endocrine system (DES) distributed throughout the body. PECs share characteristics of neural and endocrine cells, collectively referred to as neuroendocrine (NE) features. The advantage of using general NE markers is that it allows investigators to study the entire population of PECs at a time. Putative precursors of PECs are demonstrable in the proximal airways of human fetal lungs at 8 weeks of gestation, and definite cells can be seen about 2 weeks later. In PEC populations of unremarkable postnatal human lungs, minimal variation occurs from childhood to old age. However, increase in PEC numbers has been described in association with multiple diseases or pathological conditions that appear heterogeneous, but in many cases involve inflammation. The physiological studies have been hampered by the fact that PECs make up only a small fraction of pulmonary cells, are diffusely distributed throughout the bronchopulmonary epithelium, and are heterogeneous.
