2A3 and 3F9. Novel lung epithelial antigens with early upregulation in hyperoxic and radiation lung injury models.

The alveolar epithelium responds to injury by upregula¬ tion of various specialized functions: proliferation and differentiation of epithelial cells, maintenance of electroyte and water balance, secretion of surfactant and associated proteins, and metabolism of xenobiotics and toxins. Genes upregulated during lung epithelial injury caused by a variety of environmental agents may serve as sensitive biomarkers of mild epithelial damage thus allowing for timely interven¬ tion. We have developed two monoclonal antibodies (2A3 and 3F9) directed to freshly isolated alveolar type II (ATII) cells1 which identify alveolar epithelial antigens with highly upregulated expression in two rat models of lung epithelial injury: hyperoxia and radiation exposure. The 2A3 mono¬ clonal antibody identifies by enzyme-linked immunosorbent assay (ELISA) and immunofluorescence freshly isolated and early-cultured ATII cells but fails to identify the antigen in lung in vivo. Since 2A3 expression occurred only during the process of isolation and culture of ATII cells, we hypothe¬ sized that ATII cell exposure to other stressful conditions, such as lung injury models, would also lead to upregulated expression of this antigen. A rat hyperoxic lung injury model was used in which 21day-old Sprague-Dawley rats were exposed to either normoxia or hyperoxia (>95% FI02) for 8 days at sea level. Im¬ munohistochemical studies demonstrated expression of2A3 only in hyperoxia-exposed rats in alveolar material, macro¬ phages, and alveolar epithelial cells. Immuno-electron mi¬ croscopy confirmed that the alveolar material staining for 2A3 was tubular myelin. A second model of lung epithelial injury was studied: a rat lung radiation injury model. Sixto 8-week-old WAG/Rij Y rats were exposed to either a single radiation dose of 15 Gy to whole thorax or sham irradiation.