Abstract
It was recently found that certain cells in the alveolar septum of the bovine lung are enriched in prostaglandin F (PGF) synthase. In this study we used immunohistochemical techniques at both light and electron microscopic levels to further characterize the PGF synthase-positive cells. By double immunofluorescence staining of bovine lung cryostat sections, the alveolar septal cells labeled by anti-PGF synthase antibody were also intensely labeled for cytoplasmic actin but not for alpha-smooth muscle actin. This labeling pattern suggests that the PGF synthase-positive cells in the septum are "contractile interstitial cells," which resemble conventional fibroblasts but characteristically contain prominent bundles of actin filaments. Immunogold electron microscopy of ultra-thin frozen sections of bovine lung showed that alveolar interstitial cells extending long cytoplasmic processes and closely associated with alveolar capillaries were intensely labeled for PGF synthase. Capillary endothelial cells, alveolar epithelial cells, and some fibroblastic cells were devoid of labeling. On the basis of these findings, we conclude that PGF synthase is specifically expressed in contractile interstitial cells within the alveolar septum. The protein may be a useful marker for contractile interstitial cells, whose physiological function and role in various pathological conditions have not been characterized in detail.