Immunohistochemical localization of a low molecular weight surfactant-associated protein in human lung

We used an antiserum to a hydrophobic 6 KD surfactant-associated protein to localize this protein in human lung tissue. This antiserum does not crossreact with the 35 KD surfactant-associated protein. By light microscopy using the indirect immunoperoxidase technique, the protein appears to be localized within Type II alveolar epithelial cells. Staining is also detectable in alveolar macrophages and occasionally within the lumina of alveoli and bronchioles. No staining was detected within the alveolar septa or in association with blood vessels. An identical distribution is seen for the 35 KD surfactant-associated protein using an antiserum specific for that protein.