FIG. 3.

Monocytes exhibit ultrastructural features of apoptotic (B and C) and necrotic (C) cell death following exposure to 1,000 ng of C. difficile toxin A per ml. Purified monocytes were incubated for 5 h with control medium (A) or medium containing 1,000 ng of toxin A per ml (B) before they were processed for electron microscopy. Cells exhibiting morphological features characteristic of apoptosis are indicated by arrows in panel B. In panel C, the arrow indicates a cell undergoing necrotic death, with swelling of the nucleus and a lack of dense chromatin. By contrast, the adjacent cell shows features of apoptotic death, with a condensed spherical nucleus containing dense chromatin.