Morphologic organization of pulmonary granulomas in mice infected with Paracoccidioides brasiliensis.

A morphologic study of the lungs was carried out in Swiss mice infected with yeast isolated from Paracoccidioides brasiliensis (Pb18). The lung was processed 1, 2, 4, and 8 weeks after inoculation for histologic staining with hematoxylin and eosin (H&E), methenamine silver nitrate (Gomori-Grocott), and picrosirius to qualitative and quantitative analyses of the granulomas and the presence of fungal lesions. The numbers of CFUs/g counted in the lungs were 189.8 +/- 20.64, 353.6 +/- 46.21, 547.2 +/- 108.1, and 295.2 +/- 89.17 in the first, second, fourth, and eighth weeks, respectively. One week after infection, inflammatory cells and reticular and collagens fibers, the latest typical of fibrosis, were detected. After 2 and 4 weeks, a progressive intensification of the infection and fibrosis was observed, but in week 8 a more organized granuloma was evident, with macrophages, epithelioid cells, and yeasts in the central portion, and intense peripheral basophilia. Pycnotic structures typical of apoptotic bodies were observed in weeks 1 and 8. The different histologic staining used acted as a fundamental tool for the study of the morphologic organization of granuloma formation.