TGF-β-positive cells are present at Day 21. Tissue sections recovered at 21 days post instillation of sham control (A-C), S-Ag NWs (D-F) or L-Ag NWs (G-I), and stained with TGF-β immunohistochemical stain. Panels are Brightfield microscopy images of responses in tissues from rats instilled with a single dose of 1.0 mg/kg Ag NWs. Brown cells (indicated by arrows) in the alveoli (left), terminal bronchioles [TB (middle)], and pleural region (right) are TGF-β-positive. BV = blood vessel. Scale bar is 25 μm.