title: Activated human T lymphocytes exhibit reduced susceptibility to methylmercury chloride-induced apoptosis.
abstract: Mercurials have been shown to cause apoptosis in human T cells. The objective of this study was to evaluate and compare the relative susceptibility of resting versus activated T cells to methyl mercury chloride (MeHgCl)-induced cell death. Apoptosis was assessed by Hoechst 33258 and 7-AAD staining and annexin V binding. Our results show that activation of T cells by PHA, PMA, and ionomycin, or IL-2, reduces mercury-induced apoptosis by approximately 50%. We have previously shown that the underlying basis for these toxic effects involves perturbation of mitochondrial function leading to oxidative stress and the release of cytochrome c to the cytosol. Therefore, the ability of MeHgCl to alter the mitochondrial transmembrane potential (delta psi m) and to induce the generation of reactive oxygen species (ROS) was evaluated in activated T-cells. Both resting and activated cells treated with MeHgCl exhibited a decrease in delta psi m when compared to respective control cells. ROS production was elevated in resting cells following treatment with mercury; in contrast, fewer activated T cells exhibit increased levels of ROS in the presence of MeHgCl. Similarly, MeHgCl treatment resulted in the release of cytochrome c to the cytoplasm in non-activated T cells but failed to do so in the activated population. These results lead us to examine intracellular levels of bcl-2, a protein that has been shown to regulate apoptosis, presumably via its ability to associate with the mitochondrial membrane. Bcl-2 levels were found, in resting cells, to be low in the presence or absence of mercury. In comparison, activated T cells expressed elevated levels of bcl-2. The relationship between mercury-induced apoptosis in human T cells, mitochondrial dysfunction, and intracellular levels of bcl-2 are discussed.
authors.affiliation: Department of Pathology, University of Pennsylvania School of Dental Medicine, Philadelphia 19104, USA.
authors.forename: A H
authors.initials: AH
authors.lastname: Close
authors.forename: T L
authors.initials: TL
authors.lastname: Guo
authors.forename: B J
authors.initials: BJ
authors.lastname: Shenker
mesh_terms: D000328:Adult; D017209:Apoptosis / Q000235:genetics*; D015153:Blotting, Western; D018929:Cell Culture Techniques; D003574:Cytochrome c Group / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D005453:Fluorescence; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects; D008213:Lymphocyte Activation; D008564:Membrane Potentials / Q000187:drug effects*; D008767:Methylmercury Compounds / Q000506:poisoning*; D008928:Mitochondria / Q000187:drug effects; D010539:Permeability / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D013601:T-Lymphocytes / Q000187:drug effects*
chemical_list: D003574:Cytochrome c Group; D008767:Methylmercury Compounds; D017382:Reactive Oxygen Species; C004925:methylmercuric chloride