AbstractWe have recently shown that lymphocyte apoptosis induced by dexamethasone or superantigens is accompanied by reduction of mitochondrial transmembrane potential (ΔΨm) which precedes nuclear DNA fragmentation. Here, we demonstrate that fluorochromes such as 3,3′dihexyloxacarbocyanine iodide DiOC6(3) which measure ΔΨm, or fluorochromes such as hydroethidine (HE) which measure mitochondrial superoxide anion production allow the identification of thymocytes or peripheral T lymphocytes which are eliminated by apoptosisin vivo. In mice bearing transgenic α/β T cell receptor (TCR) specific for a class I‐restricted male‐specific peptide, the superoxide‐mediated oxidation of HE into ethidium (Eth) is enhanced among thymocytes which are being deleted due to negative selection (CD4+CD8+cells expressing the transgenic TCR in male mice) or lack of positive selection (CD4+CD8−thymocytes from female mice). ΔΨmreduction and/or enhanced HE oxidation are also found when apoptosis is induced by a series of pathogenic agents. Thus, lethal irradiation provokes mitochondrial and nuclear signs of apoptosis, and both these alterations are absent in mice bearing a p53 null mutation, underlying the correlation between mitochondrial perturbation and nuclear apoptosis. Similarly, superantigen‐triggered deletion of peripheral T cellsin vivois accompanied by enhanced HE → Eth conversion and reduced DiOC6(3) uptake. More importantly, as compared to normal controls. CD4+or CD8+cells from clinically asymptomatic human immunodeficiency virus‐1 (HIV‐1) carriers also contain a significantly elevated percentage of cells endowed with reduced DiOC6(3) uptake. In superantigen‐ and HIV‐induced apoptosis, the percentage of T lymphocytes with a subnormal DiOC6(3) uptake is more important than that of cells marked by enhanced HE → Eth conversion. In conclusion, mitochondrial alterations precede and/or accompany nuclear signs of apoptosis induced by physiological and a variety of dif
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