Fig. 3.

Pulmonary histopathology in hMPV challenged cotton rats vaccinated with FI-hMPV. Lung in the top row from previously untreated animals or the bottom row from animals that received mock vaccine shows lymphocytes around the bronchiole (peribronchiolitis) at day 4 that is cleared by day 10. The second row shows lung from an animal previously infected with metapneumovirus, and the peribronchiolitis is accentuated and continues through day 7, but largely cleared by day 10. Mild interstitial pneumonitis and alveolitis is present at day 4 only. The third row shows the lung from an animal immunized with formalin-inactivated vaccine and challenged. There is marked accentuation of peribronchiolitis and perivasculitis continuing through day 10, thickening of alveolar walls (interstitial pneumonitis), and a cellular infiltrate in alveoli (alveolitis).