FIG. 4.

Electron micrographs of PMNs. (A) Uninfected PMNs as a control. (B) PMNs 1 h after infection with the CHA strain, showing features of oncosis: dispersed chromatin within swollen nucleus, vacuolization, and absence of cell membrane. (C) PMNs 1 h after infection with the CHA-D1 strain. (D) PMNs heated for 30 min at 56°C, showing oncotic cell death morphology with the same profile as in the CHA-infected cells. (E and F) PMNs, treated with actinomycin D, showing either early apoptotic morphology with intense perinuclear chromatin aggregation but cytoplasm integrity (E) or late apoptotic morphology characterized by degenerated nuclei, where the chromatin is completely aggregated as in early apoptosis, but dissolution of the cytoplasm (F). The arrow indicates bacteria. Bars, 1 μm.