Fig. 4
Microscopic findings of non-neoplastic lesions in the lung and pleura of MWNT-7-treated rats. A–C Representative histological images of the lung in rats of the control (A), low-dose (B), and high-dose (C) groups at week 26. Foci of reactive alveolar hyperplasia are scattered (arrowheads). The proliferation of the alveolar epithelium is evidenced by an increase in the immunopositivity of the nuclei for TTF-1 in the MWNT-7 treated groups (insets). D Marked MWCNT depositions in the alveolar regions of the lung of a rat in the high-dose group. Inset: a polarized light microscope image. E Bronchiolization (low-dose group). F Atypical hyperplasia (high-dose group). Epithelial cells form irregular structures (often glandular structures) with fibrous connective tissue proliferations and MWCNT depositions. G MWCNT depositions in a BALT (arrow; high-dose group). H MWCNT fiber piercing the visceral pleura (arrow) (high-dose group). Kernechtrot staining. Inset: polarized light microscope image. I MWCNT depositions in a mediastinal lymph node (arrow; high-dose group). J Thickened mesothelium of the RPF (high-dose group). Enlarged mesothelial cells and inflammatory cells such as lymphocytes and eosinophils are seen. K Focal fibrosis of the diaphragm (low-dose group). The lesion is lined by enlarged and ciliated mesothelial cells. L Thickened visceral pleura with a fibrotic change (high-dose group). Monocytes, enlarged mesothelial cells, and MWCNT-engulfing macrophages (arrows) are notable. M Thickening of the mediastinal pleura containing hyperplastic lesions (high-dose group). N Higher magnification of (M). Several focal hyperplasias can be seen as protrusions (arrows). (N1) Immunostaining for mesothelin. O Higher magnification of (N). Layered or bulging mesothelial cells with atypia are underlain by a thickened submesothelial area. MWCNT fibers phagocyted by macrophages are distributed (arrows). Insets: polarized light microscope images. All images were obtained from animals sacrificed at week 104, except (A), (B), and (C)