C57BL/6 WT mice received 0 or 15 Gy WTI and were sacrificed at the indicated time points post-irradiation. (A) CD73 histochemistry on lung frozen sections of irradiated and control mice using 5'-AMP or 5'-AMP (negative control) as substrates. CD73 activity is visualized by the black lead sulfide precipitate. (B) Lung CD73 enzyme activity at the indicated time points (n = 12/12, 9/9, 10/9, 5/4, 19/13 [0 Gy/15 Gy]). (C) Fold change of BALF adenosine levels (mean ± SEM) of irradiated vs. control mice. Means of control values were between 41 and 149.5 nM (n = 9/10, 7/7, 10/9, 8/7, 20/11 [0 Gy/15 Gy]). *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001 by two-way ANOVA followed by post-hoc Bonferroni test. (D) Masson´s Goldner Trichrome (MT) and H&E staining of paraffin-embedded lung sections (scale bar = 100 µm).