Ozone exposure enhances expression of cell-surface molecules associated with antigen-presenting activity on bronchoalveolar lavage cells in rats

In this study, we investigated the effects of ozone (O-3) exposure on expression of cell-surface molecules associated with antigen presentation and on accessory activity of bronchoalveolar lavage cells (BAL cells). Rats were exposed to 1 ppm O-3 for 3 days. Expression of cell-surface molecules was measured by flow cytometry. Accessory activity of BAL cells was assessed by the allogeneic mixed lymphocyte reaction (MLR) and specific antigen-presenting activity. O-3 exposure increased the expression of Ia, B7.1, B7.2, and CD11b/c on BAL cells. Morphological and immunological studies showed the Ia-positive cells to have monocyte-like features. Peripheral blood monocytes expressed Ia, B7.1, B7.2, and CD11b/c. The Ia expression on the monocytes was further increased by treatment of them with BAL fluid from O-3-exposed rats (O-3-BALF). Resident alveolar macrophages, however, did not express Ia antigen, and the Ia expression was not increased by O-3-BALF. Neutrophils, which also infiltrated in response to O-3 exposure, did not express Ia, B7.1, and B7.2. Therefore, infiltrating monocytes may have caused the increased expression of Ia and B7 molecules on BAL cells exposed to O-3. The accessory activity of BAL cells in terms of MLR and specific antigen-presenting activity was also enhanced by O-3 exposure. The present study suggests that monocytes infiltrating in response to O-3 exposure caused enhancements of the expression of Ia and costimulatory molecules on and the accessory activity of BAL cells.