Figure 2

emphysema over time in the titratable PPE model. (A) Mice treated with only 500 µL of tracheal PBS (zero activity units of PPE) had a small but not significant increase in mean linear intercept (MLI) between days 21 and 84 post-administration. Dashed line represents 21 day PBS MLI. (B) A representative 10X photomicrograph from 21 and (C) 84 days. (D) While the MLI of mice treated with 0.5 units of PPE was slightly more than that of mice treated with PBS (dashed line), there was a small but significant increase in MLI at 84 days. (E) A representative 10X photomicrograph from 21 and (F) 84 days. (G) A larger increase in MLI was seen in mice treated with 2 units of PPE, and a larger increase over time was also seen. (H) A representative 10X photomicrograph from 21 and (I) 84 days. (J) Emphysema at 21 days and increase at 84 days was even greater after treatment with 4 units of PPE. (K) A representative 10X photomicrograph from 21 and (L) 84 days. (M) The increase in MLI at 21 days was not significant between PBS and 0.5 units of PPE but was significantly higher for 2 and 4 units. (N) These differences were more pronounced at 84 days. (O) Each mouse had 20 MLI measurements made of its lungs. The variability in these measures increased with greater emphysema. **p < 0.01, ***p < 0.001, ****p < 0.0001 by Welch’s t-test for 2-group and by holm post hoc test after ANOVA for 4-group comparisons.