MMP-9 immunolocalization. Mice were killed 14 days after saline or bleomycin exposure, and the lungs were lavaged and processed for MMP-9 immunolocalization. Immunoperoxidase detection using a MMP-9 antibody was used to localize MMP-9 (brown stain) to inflammatory cells in the lungs of (A) A3R+/+ mice exposed to bleomycin and (B) A3R−/− mice exposed to bleomycin. The same antibody was used in an immunofluorecence assay to examine MMP-9 expression (green) in BAL cells from (C) A3R+/+ mice exposed to bleomycin and (D) A3R−/− mice exposed to bleomycin. Blue staining denotes DAPI-stained nuclei. Mast cells were localized in bronchi of (E) A3R+/+ mice exposed to bleomycin and (G) A3R−/− mice exposed to bleomycin using tolidine blue staining. MMP-9 immunoperoxidase detection (brown stain) was used to localize MMP-9 to mast cells in the bronchi of (F) A3R+/+ mice exposed to bleomycin and (G) A3R−/− mice exposed to bleomycin. n, neutrophils; Φ, macrophages; arrows denote mast cells. Scale bars: A and B, 50 μm; C and D, 10 μm; H, 10 μm (also applies to E–G).