Expression of inducible nitric oxide synthase and nitrotyrosine during theevolution of experimental pulmonary tuberculosis

Nitric oxide (NO) is a relevant antimycobacterial factor in mouse macrophag es, NO is a product of inducible nitric oxide synthase (iNOS). NO toxicity is greatly enhanced by reacting with superoxide to form peroxynitrite that reacts with many biological molecules. Tyrosine is one of the molecules wit h which NO reacts and the product is nitrotyrosine (NT). The production of peroxynitrite and the nitrosylation of proteins might play a role in bacter ial killing and also in mediating host injury. In this study, we used a wel l-characterized mouse model of pulmonary tuberculosis to examine the local kinetics of expression and cellular distribution of iNOS and NT at the cell ular and subcellular level. The histopathological study showed two phases o f the disease: early and late. The early phase was characterized by mononuc lear inflammation and granuloma formation. During this phase, high percenta ges of activated macrophages were observed that were immunostained for iNOS and NT. Immuno-electronmicroscopy showed NT immunoreactivity in lysosomes and mycobacterial wall and cytoplasm. The concentration of iNOS mRNA and NO metabolites were also elevated. The late phase was characterized by progre ssive pneumonia with focal necrosis and a decrease of iNOS mRNA and NO meta bolites. The strongest NT immunostained areas were the necrotic tissue. Mac rophages became foamy cells with scarce iNOS immunostaining but strong NT i mmunoreactivity. At the ultrastructural level, these cells showed NT immuno labeling in cytoskeleton, mitochondria, lysosomes and cell membrane. NT was also located in bronchial epithelial cell mitochondria, in cell membranes and cytoplasm of endothelial cells and in actin bundles within smooth muscl e cells. These results suggest an important role of NO in mycobacterial kil ling, particularly during the early phase of the infection. They also sugge st an important participation by NO in tissue damage during the late phase of the disease.