Figure 1. Haematoxylin and eosin staining of paraffin-embedded brain tissue from a hypoxia-treated neonatal pig is demonstrated. Neuronal cell apoptosis is indicated with an arrow. The cell is shrunken, the cytoplasm condensed and eosinophilic, and several spots of condensed nuclear chromatin are easily visible. The other neuronal cell nuclei seen here are normal. The long thin cell under the arrow is likely a structural cell such as a glial cell.

Figure 2. (a) A single apoptotic cell is demonstrated (arrow) in the tubular epithelium of a human kidney (light microscopy of paraffin section stained with Periodic acid-Schiff reagent). (b) Apoptotic bodies (arrowed) have been phagocytosed by an adjacent viable cell, whose nucleus is visible (n). In the lower apoptotic body (large arrow), lysosomal degradation of the phagocytosed nuclear material is seen, in comparison with the upper apoptotic bodies (smaller arrows) where crescents of compacted nuclear chromatin can still be seen by transmission electron microscopy. (c) The irregularly clumped nuclear chromatin of necrosis (called karyorrhexis) is seen in a cell in tissue culture. Note the loss of membrane definition of both the cell and the nucleus (method is transmission electron microscopy).

Figure 3. Electron microscopy of apoptotic B-cell lymphoma cell treated in cell culture with etoposide, showing plasma membrane degradation around the apoptotic cell. This often occurs in cell culture some time after the structural changes of apoptosis can be detected, and is the start of a degradative change called ‘secondary necrosis’. Note here that the typical nuclear changes of apoptosis (condensation and margination of the chromatin along the nuclear membrane) are still visible. From unpublished work of Alan Blood, Department of Molecular and Cellular Pathology, University of Queensland 1998.

Figure 4. (a) A diagram is shown of possible outcomes of apoptosis in a monolayer cell culture. The apoptotic cell in the centre of the monolayer is showing rounding, loss of surface microvilli, cytoplasmic condensation and fragmentation of the nucleus. An apoptotic body is seen blebbing away from the layer of cells into the supernatant (*), and another apoptotic body is seen being phagocytosed by an adjacent viable cell (arrow). (b) and (c) Apoptosis is often analysed in cell culture. (b) Normally growing suspension culture cells show some cytoplasmic vacuolation but the nuclei, some with multiple nucleoli, are healthy. (c) The same cells treated with cisplatin show apoptosis (some examples arrowed). There is evidence of pale cell debris in the background of (c). This demonstrates secondary degradation in some of the apoptotic cells (one demonstrated with *) where there remains typical nuclear condensation of apoptosis, but the cytoplasm is now pale and degraded.

Figure 5. (a) The tubular epithelium and interstitium of the kidney after ischemia-reperfusion have many cells with nuclei positively labelled for TUNEL (arrow heads). (b) Renal tubular epithelial cells in culture have been treated with 1 mM hydrogen peroxide for 16 h. Apoptotic nuclei labelled with TUNEL are arrowed. The counterstain of haematoxylin stains all other nuclei blue. The cytoplasm of the cells cannot be seen as it is unstained.

Figure 6. Immunohistochemistry against activated, or cleaved, caspase-3 is often used as a molecular marker of apoptosis. Here several apoptotic leucocytes (arrowed) have labelled positively for activated caspase-3 in a small blood vessel of rat heart after endotoxin treatment.