Lung histopathology at the early chronic stage of infection by highly virulent Mtb strain M299.

<p>Pathological alterations to lung tissue were observed on day 120 after infection by microscopic analysis of lung sections stained by hematoxylin-eosin (<b>A</b> and <b>B</b>), Masson´s trichrome (<b>C</b>) and Ziehl-Neelsen (<b>D</b>). Panel <b>A</b> demonstrates a necrotic lesion (black star) partially healed by fibrosis and surrounded by a rim of lymphocytes and lipid-laden foamy macrophages in the external region. Secondary granulomatous lesions are marked by white stars. Panel <b>B</b> demonstrates a higher-magnification image of two compact perivascular lymphocyte granulomas, surrounded by foamy macrophages. <b>C</b>. Masson’s staining revealed the presence of profuse collagen (in light-blue) in the central area of the necrotic lesion. Note cellular debris in the bronchiole and the absence of a bronchiolar epithelium (black arrow). <b>D</b>. Single AFB, exhibiting weak staining (black arrow heads), could be seen in necrotic areas partially healed by fibrosis and in foamy macrophages within alveoli. Bars represent 500 μm- in the panel <b>A</b>, 200 μm- in the panels <b>B</b> and <b>C</b>; and 100 μm- in the panel <b>D</b>.