FIG 8.

Proliferation of lung epithelial cells measured by the Ki-67 labeling index. (Top) Images representative of the scoring system (labeling index scores 0 to 3) used to grade the extent of lung cellular proliferation (Ki-67 antigen positivity) in immunohistochemical sections taken from ferrets infected with 10⁶ TCID₅₀s of the H1N1pdm virus (A/KY/180/2010). Bar, 50 μm. (Bottom) The left and right cranial, left caudal, and middle lobes were taken at necropsy (at 0.25, 1, 2, 3, and 7 dpi) and were prepared for histology. Bronchi, bronchioles, and alveolar spaces were analyzed in the lobes of each ferret per time point (18 to 50 images [not shown] per anatomic region per time point). The images were scored by two independent observers for the levels of Ki-67 positive cells. Shown is the mean proliferation index per anatomic region over time (error bars represent the standard errors of the means). Asterisks indicate a significant difference (***, P < 0.01) from the score for mock-infected animals by a nonparametric statistical test.