Abstract
Macrophages and α-smooth muscle actin immunopositive myofibroblasts are thought to be crucial cells in granuloma formation. In this study, the reactive cell kinetics was investigated in Sephadex bead-induced rat pulmonary granulomas (1mg/ml saline/head; intravenously) from l hour to 90 days after the injection. Intravenously administered Sephadex beads occluded pulmonary arteries and caused granulomatous pulmonary arteritis. The inflammatory cells appeared first around the trapped beads and then granuloma lesions developed within 24 hours. Three days later, the granulomas mainly consisted of neutrophils, macrophages, eosinophils, and giant cells. Immunohistochemically, the number of ED1-positive macrophages quickly increased 24 hours after the injection, and a large number of macrophages were still found 3 days after the injection. Alpha-smooth muscle actin immunopositive myofibroblasts increased in numbers from 3 to 7 days after theinjection. These results indicate that the appearance of myofibroblasts in pulmonary granulomas might be mediated by macro-phages, which were the most predominant inflammatory cells in the present pulmonary granuloma.
