Transmission electron micrographs of lung tissue from mice with OVA-induced eosinophilia. Control mice treated with the isotype control Ab showed no sign of eosinophil apoptosis at 8 h (A) and 24 h (not shown). In mice treated with anti-Fas mAb there were numerous apoptotic eosinophils in the lung tissues at both 8 and 24 hours after treatment (B and C, respectively). The apoptotic eosinophils were rarely engulfed although macrophages (labeled M) commonly occurred in the tissue (B). By 24 h a majority of the apoptotic eosinophils exhibited signs of secondary necrosis and severe inflammation was recorded including neutrophil infiltration (arrow) and derangement of the epithelial lining (labeled E).