Blockade of IL-22 reverses protection of Il17a^−/− mice from bleomycin-induced pulmonary inflammation. Il17a^−/− mice were intratracheally instilled with bleomycin, treated with an isotype control (Iso) or anti–IL-22 (αIL-22) mAb, and sacrificed on day 10. (A) BAL cell counts. (B and C) Neutrophil infiltration was assessed by H&E staining of BAL cell cytocentrifuge preparations (B; highlighted by white arrows) and by flow cytometry of lung cells for the frequency (left) and total number (right) of Gr-1⁺ cells (C). Bars, 10 µm. (D) H&E staining of histological lung sections demonstrating peribronchial leukocyte infiltrate (black arrows), disruption in lung architecture (white arrows), and epithelial hyperplasia (gray arrow). Bars, 100 µm. (E) Weight loss of individual mice was plotted as a percentage of starting weight. (F) Total pathology score. All data are representative of three or more independent experiments with a minimum of three to five mice per group. Data shown are means ± SEM. *, P < 0.05.