Treatment with AAV9-Tert restores the proliferation of AT II cells, macrophages, and club cells and reduces the differentiation of club cells. (A) Representative immunostainings for SFTPC (purple), F4/80 (brown), and Ki67 (blue; orange and blue arrowheads indicate double SFTPC-Ki67– and F4/80-Ki67–positive cells, respectively; left); SCGB1A1 (purple) and Ki67 (blue; green arrowheads indicate double SCGB1A1-Ki67–positive club cells; center); and SCGB1A1 (blue) and SOX2 (brown; red arrowheads indicate double SCGB1A1-SOX2–positive club cells; left) in lungs of Tert^+/+ and G3 Tert^−/− mice treated with the AAV9-Tert (upper panels) or AAV9-empty (lower panels). (B–E) Quantification of SFTPC-Ki67–positive (B), F4/80-Ki67–positive (C), SCGB1A1-Ki67–positive (D), and SCGB1A1-SOX2–positive (E) cells. (F–K) Changes in total lung mRNA expression levels of Tnf (F), Il1b (G), and Il6 (H; proinflammatory markers) and Il4 (I), Il10 (J), and Il13 (K; anti-inflammatory markers) normalized to 18S expression and (L–O) protein levels of TNF (L), IL-6 (M), IL-4 (N), and IL-10 (O) assessed in lung homogenates from AAV9-empty– and AAV9-Tert–treated animals. Quantifications were performed on five different alveolar areas or bronchi in a random way. Data are expressed as mean ± SEM (n = 4–5 animals per group). *, P < 0.05; **, P < 0.01; ***, P < 0.001 (Shapiro–Wilk, Kruskal–Wallis, and Dunn–Sidak multiple comparison test). ns, not significant.