Human SP-A is expressed in alveolar epithelial type II cells and in tracheal and bronchial submucosal gland cells in lung as well as in other tissues. SFTPA1(SP-A1) and SFTPA2(SP-A2) are expressed in the type II cells; SP-A2 is expressed in human tracheal and bronchial submucosal gland cells. The presence of SP-A in non-ciliated bronchiolar epithelial cells has been inconsistent for human lungs, but consistent positive staining of SP-A has been observed in the non-ciliated bronchiolar epithelial cells in rodents.
