IN-SITU DETECTION OF FRAGMENTED DNA (TUNEL ASSAY) FAILS TO DISCRIMINATE AMONG APOPTOSIS, NECROSIS, AND AUTOLYTIC CELL-DEATH - A CAUTIONARY NOTE

Detection of DNA fragments in situ using the terminal deoxyribonucleot idyl transferase (TDT)-mediated dUTP-digoxigenin nick end labeling (TU NEL) assay is increasingly applied to investigate active cell death (a poptosis). We studied the specificity of the assay in well-defined mod els of apoptosis and necrosis as well as in postmortem autolysis in ra t liver. During involution of liver hyperplasia, which follows stoppin g treatment with the hepatomitogens cyproterone acetate (CPA) or nafen opin (NAF), numerous apoptotic hepatocytes could be observed with TUNE L-positive chromatin residues. A similar TUNEL-positive reaction appea red in necrotic hepatocytes after a cytotoxic dose of carbon tetrachlo ride (CCl4) or N-nitrosomorpholine (NNM). Also, in insufficiently fixe d, autolytic livers TUNEL-positive nuclei were observed. Thus, DNA fra gmentation is common to different kinds of cell death; its detection i n situ should not be considered a specific marker of apoptosis.