Pulmonary response to ozone: reaction of bronchus-associated lymphoid tissue and lymph node lymphocytes in the rat

The purpose of this work is to assess the effect of ozone, a reactive product of environmental photochemical oxidation, on lymphocytes of the lung. We exposed male Fischer rats to ozone at a concentration of 0.5 ppm for 20 hr/day for 1-14 days. Animals were treated with radioactive thymidine and were sacrificed at Day 1, 2, 3, 7, or 14 of exposure. Lungs and mediastinal lymph nodes were removed and prepared for histologic examination, evaluation of labeling indexes, and morphometric measurement. We examined two components of the lymphocyte response of the lung: the airway-related response, represented by the reaction of the bronchus-associated lymphoid tissue (BALT), and the deep lung-related response, represented by reaction of the mediastinal lymph node. Lymphocytes of both the BALT and the mediastinal lymph node showed elevated radioactive thymidine uptake; however, no evidence of cell death was observed at either site. The cells of the specialized epithelium covering the BALT (lymphoepithelium) showed increased vacuolization, indicating altered cellular function. The average size of BALTs was unchanged by ozone exposure. Under experimental conditions ozone can affect a variety of cells in the lung including bronchial epithelial cells, macrophages, and Type 1 cells. We have shown for the first time that in addition to these cells, the rat BALT also proliferates in response to ozone. In addition we confirm previous work in the mouse which shows that the mediastinal lymph node reacts as well. The airways can be affected by inflammation, can be targets of infection, and can respond to chemical irritants with bronchoconstrictive responses. They are an important target organ for hypersensitivity responses and are a primary site for pulmonary cancer formation. A role for lymphocytes has been implicated in each of these processes. Therefore, the clinical significance of ozone on BALT and mediastinal lymph node responses could be appreciable in terms of potentiation of, or protection against, such responses.