Decreased GSNO reductase immunoreactivity in lung-cancer specimens. (A) Airway tissue from healthy, nonsmoking adults expresses epithelial GSNO reductase (brown stain; ×20). (B and C) Wild-type (wt) mice (B), but not GSNO reductase−/− mice (C), express pulmonary GSNO reductase in their lungs. (D) A representative neutrophil is GSNO reductase–negative. (E) A representative macrophage is GSNO reductase–positive. (F) Inflammatory cells that immunostain positively serve as a positive internal control in lung-cancer specimens (in this case, squamous-cell carcinoma). (G) Examples of squamous-cell carcinoma specimens with reduced GSNO reductase immunoreactivity. (H) This decreased GSNO reductase expression is true for a range of cancers, including squamous-cell carcinoma, adenocarcinoma and large-cell (undifferentiated) carcinoma (top, ×40; bottom, ×10).