Fig 4.

Immunohistochemistry of 1918 TIV-immunized and control ferrets following 1918 virus challenge. Photomicrographs of lung tissue sections from control (A to D) and TIV-immunized (E and F) ferrets stained (in red) for the presence of viral antigen 3 and 5 days p.c. Viral antigen was found in bronchiolar epithelial cells and in desquamated cells in the lumen of bronchioles on day 3 p.c. (A and B), in cells of submucosal serous glands of the bronchus on day 5 p.c. (C), and in alveolar cells and macrophages on day 5 p.c. (D). TIV-immunized ferrets challenged with the 1918 virus examined at day 3 p.c. displayed milder lung lesions than controls, with no specific viral antigen staining detected on day 3 p.c. (E) and day 5 p.c. (F).