(A) Dosing schematic for single-dose bleomycin exposure for wild-type and IL-6–deficient (IL-6KO) mice. (B) Dosing schematic for repeated-dose bleomycin exposure for wild-type and IL-6KO mice. (C) Representative images for Krt5+-stained wild-type and IL-6KO mouse lungs after single-dose bleomycin injury. Immunofluorescence staining of DAPI (blue) and Krt5 (red) in the distal airways and parenchyma. Scale bars, 100 μm. (D) Representative images for Krt5+-stained wild-type and IL-6KO mouse lungs after repeated-dose bleomycin injury. Scale bars, 100 μm. (E) Quantification of Krt5+ area in the mouse lung after single- or repeated-dose bleomycin for wild-type (single dose, n = 10; repeat dose, n = 9) and IL-6KO (single dose, n = 12; repeat dose, n = 7) mice. Error bars represent 95% confidence interval. One-way ANOVA was used for statistical comparisons. (F) Quantification of hydroxyproline in the mouse lung after single- or repeated-dose bleomycin for wild-type (single dose, n = 14; repeat dose, n = 9) and IL-6KO mice (single dose, n = 14; repeat dose, n = 7). Error bars represent 95% confidence interval. One-way ANOVA was used for statistical comparisons. (A to E) For all statistical analysis n.s. (not significant), **P < 0.01, ***P < 0.001, ****P < 0.0001.