TOXICOLOGY AND APPLIED PHARMACOLOGY 139, 317–323 (1996) ARTICLE NO. 0171 Inhibition of Human T Lymphoblast Proliferation by Hydroquinone 1 QING LI,* , ²L ISA GEISELHART,* , ‡JAMES N. MITTLER,§ STANLEY P. MUDZINSKI,§ DAVID A. LAWRENCE, Ø AND BRIAN M. FREED* ,  ,2 *Transplantation Immunology and HLA Laboratory, Departments of Surgery, ² Pathology and Laboratory Medicine, and ‡Microbiology, Immunology, and Molecular Genetics, and §Cellular Immunology Laboratory, Albany Medical College, Albany, New York 12208; and Ø Wadsworth Center, New York State Department of Health, Albany, New York 12201 Received December 8, 1995; accepted April 19, 1996 burden of benzene, with another 20% of the burden resulting Inhibition of Human T Lymphoblast Proliferation by Hydroqui- from automobile travel, pumping gasoline, and living in none. LI, Q., GEISELHART, L., MITTLER, J., MUDZINSKI, S. P., houses with attached garages (Wallace, 1989). Although LAWRENCE, D. A., AND FREED, B. M. (1996). Toxicol. Appl. Phar- benzene is typically associated with myelotoxicity, inhibi- macol. 139, 317–323. tion of T- and B-cell responses in benzene-treated animals occurs in the absence of leukopenia or lymphocytopenia Hydroquinone (HQ) is a major metabolite of benzene and is present in large quantities in cigarette tar as a result of the combus- (Rozen et al., 1984; Aoyama, 1986; Rosenthal and Snyder, tion of tobacco leaf pigments. We hypothesize that the immuno- 1987; Hsieh et al., 1988), suggesting that lymphocyte re- suppressive effects of cigarette smoking are due, in part, to the sponses may represent the most sensitive level of benzene deposition of large quantities of HQ in the lungs. Exposure of immunotoxicity. This hypothesis is further supported by the primary human T lymphoblasts (HTL) in vitro to 50 mM HQ observation that the inhalation of cigarette smoke preferen- blocked IL-2-dependent proliferation by ú90% with no loss in tially suppresses the Con A response of lung lymphocytes, viability. Inhibition of DNA synthesis was observed immediately with little or no effect on the response of peripheral lympho- after the addition of HQ to the cells. However, this effect could cytes (Daniele et al., 1977). The immunosuppressive charac- be reversed up to 6 hr later by simply washing the cells and recul- teristics of cigarette smoke are not associated with either turing them in the absence of HQ. HQ did not significantly alter decreased numbers or viability of T cells in the lungs (Da- intracellular glutathione levels up to 24 hr later, and the presence of 50 mM 2-mercaptoethanol or 500 mM dithiothreitol during the niele et al., 1977). treatment did not prevent inhibition of DNA synthesis. HQ did Studies from a number of laboratories have clearly shown not block binding of 125 I-IL-2 to the cells, but inhibited the IL-2- that the metabolites of benzene, rather than the parent com- dependent progression of HTL through S phase of the cell cycle. pound, are responsible for both the immunosuppressive and These observations demonstrate that HQ, in concentrations com- myelotoxic effects (Snyder and Kocsis, 1975; Tunek et al., parable to those found in cigarette tar, is a potent inhibitorof IL- 1978; Rickert et al., 1979; Irons et al., 1979; Greenlee and 2-dependent T cell proliferation and may therefore help to explain Bus, 1980; Irons and Pfeifer, 1982). The metabolites of ben- the potent immunosuppressive effects of cigarette smoke on lung zene differ considerably in immunosuppressive activity. Hy- T lymphocytes.  1996 Academic Press, Inc. droquinone (HQ), 1,2,4-benzenetriol (BT), and catechol sup- press the in vitro response of rat spleen cells to PHA at concentrations between 10 and 100 mM, while benzene and Among the organic compounds with known immunotoxic phenol exhibit no inhibitory effects at concentrations as high properties, benzene is produced in the largest quantities and as 1 mM (Pfeifer and Irons, 1981; Post et al., 1985). The has the widest human exposure. A recent report by the Envi- strict requirement for more than one hydroxyl group suggests ronmental Protection Agency indicated that the tar in ciga- that the immunosuppressive activity of the polyhydroxy me- rette smoke accounts for almost 50% of the total population tabolites may be due to further oxidation to thiol-reactive quinones. This hypothesis, initially proposed by Irons and Pfeifer (1982), is supported by several observations. First, 1 This work was supported by United States Public Health Service NIH Grant ES-05673 from the National Institute of Environmental Health Sci- p-benzoquinone (p-BQ) is ú2-fold more inhibitory than HQ ences, National Institute of Health. in vitro (Irons and Pfeifer, 1982). Second, the inhibitory 2 To whom correspondence should be addressed at Transplantation Im- effect of HQ on in vitro mitogenic responses of rat spleno- munology and HLA Laboratory, Room ME-524 (A-62), Albany Medical cytes can be blocked by coadministration of the thiol-reac- College, Albany, NY 12208. Fax: (518) 262-6274. E-mail: transimm@aol. com. tive agent, dithiothreitol, suggesting that electrophilic p-BQ 317 0041-008X/96 $18.00 Copyright  1996 by Academic Press, Inc. All rights of reproduction in any form reserved.