Figure 3

The lung histopathology as shown by H-E and Masson's trichrome staining after H5N1 infection in mice. On day 7 p.i., infected mice presented typical diffuse pneumonia with interstitial edema around small blood vessels (Figure 3A, solid arrow) and inflammatory cells in thickened alveolar walls (Figure 3A, open arrow). On day 14 p.i., Masson's staining showed widened alveolar spaces with collagen fibers (Figure 3B, open arrow), and thickened alveolar walls with infiltration of inflammatory cells and hyperplasia of pneumocytes (Figure 3B, solid arrow). On day 30 p.i., severe distortion of structure and diffuse fibrous areas were observed in lung fields (Figure 3C) at low magnification. Some animals displayed typical interstitial fibrosis in lungs, characterized by greatly thickened alveolar walls with cell proliferation and matrix accumulation in interstitial space (Figure 3D, solid arrow). The diffuse intra-alveolar fibrosis was a common finding, with an excessive collagen deposition and cell proliferation in airspaces that obliterated the alveolar spaces and severely distorted the structure (Figure 3E and 3F, solid arrows; Figure 3D and 3G, open arrows). The thickened bronchiolar walls with proliferated fibroblasts lead to bronchiolar stenosis (Figure 3G, solid arrow). In addition, focal alveolar collapse (Figure 3H, solid arrows) and alveolar ectasia (Figure 3D and 3H) were observed simultaneously in some sections. Original magnification: A, E, G, H-E × 200; D, F, H-E × 400; C, Masson × 100; H, Masson × 200; B, Masson × 400.