EXTRACELLULAR GLUTATHIONE-PEROXIDASE IN HUMAN LUNG EPITHELIAL LINING FLUID AND IN LUNG-CELLS

The epithelial cells of the lower respiratory tract are exposed to hig h levels of inhaled oxygen and other oxidants. We hypothesized that lu ng cells would secrete the antioxidant enzyme, extracellular glutathio ne peroxidase (eGPx), into epithelial lining fluid (ELF). To investiga te this hypothesis, we used specific immunoprecipitations of GPx enzym es from ELF, specific immunoprecipitations of Se-75 metabolically labe led proteins from lung cells in culture, and in situ hybridization, No rthern blot, and reverse transcription-polymerase chain reaction (RT-P CR) analyses. Fifty-seven percent of ELF GPx activity was due to eGPx and 40% was due to cellular GPx (cGPx). Primary bronchial epithelial c ells (BEG), primary alveolar macrophages (AM), and two human bronchial epithelial cell lines, BEP2D and A549, synthesized both eGPx and cGPx and secreted eGPx into the medium. Freshly isolated human AM and BEC expressed eGPx mRNA, while freshly isolated rabbit type 2 pneumocytes did not. In lung tissue, eGPx mRNA was found mainly in interstitial ce lls of tissue surrounding airways. It is concluded that more than half of GPx activity in BAL is due to eGPx, and that BEG, AM, and intersti tial cells are potential sources of pulmonary eGPx.