Int. J. lrnmunopharmac., Vol. 13, No. I, pp, 109-115, 1991. Printed in Great Britain. 0192-0561/91 $3.00 + .00 Pergamon Press plc. International Society for lmmunopharmaeology. ALTERATIONS IN MITOGEN-INDUCED CALCIUM MOBILIZATION AND INTRACELLULAR FREE CALCIUM PRODUCED BY 7,12-DIMETHYLBENZ(a)ANTHRACENE IN THE JURKAT HUMAN T CELL LINE* SCOTT W. BURCHIEL, ~ T. ANTHONY THOMPSON and DE ANN P. DAVIS University of New Mexico College of Pharmacy Toxicology Program - - Immunotoxicology Laboratory, Albuquerque, NM 87131, U.S.A. (Received 28 February 1990 and in final form 21 June 1990) Abslract -- The purpose of these studies was to assess the effects of 7,12-dimethylbenz(a)anthracene (DMBA), an immunosuppressive polycyclic aromatic hydrocarbon (PAH), on Ca ~ z mobilization induced by phytohemagglutinin (PHA) in the Jurkat human T cell line. Intracellular levels of free cytosolic Ca ~z were examined by flow cytometry using Indo-1 loaded cells. At doses of 3 - 30/aM, DMBA was found to produce a dose and time-dependent inhibition of Ca +2 mobilization in Jurkat following in vitro exposure. The decrease in Ca ~z mobilization was correlated with an increase in baseline levels of cytoplasmic free Ca +2. Two non-immunosuppressive PAHs, benzo(e)pyrene and anthracene, failed to inhibit PHA-induced Ca ÷2 mobilization or alter baseline levels of free Ca .2. These results suggest that DMBA may produce immunosuppression by inhibiting Ca ~2 mobilization or by altering Ca ~2 homeostasis in activated T cells. Previous studies have shown that polycyclic aromatic hydrocarbons (PAHs) are suppressive to the immune system of several species (White, Lysy & Holsapple, 1985; Wodjani & Alfred, 1984; Ward, Murray & Dean, 1985). Our interests have focused on the immunosuppression produced by 7,12-dimethyl- benz(a)anthracene (DMBA), which has been shown to inhibit both humoral (Ward et al., 1985; Thurmond, Lauer, House, Cook & Dean, 1987; Burchiel, Hadley, Barton, Fincher, Lauer & Dean, 1988) and cell-mediated immunity in mice (Ward, Murray, Lauer, House & Dean, 1986; House, Lauer, Murray & Dean, 1987). While the mechanism of immunosuppression by DMBA has not been elucidated, results from our laboratory (Burchiel et aL, 1988; Burchiel, Davis, Gomez, Montano, Barton & Seamer, 1990) as well as those from others (House et al., 1987; House, Pallardy & Dean, 1989) suggest that DMBA may produce inhibitory effects on T lymphocytes. It has been known for several years that DMBA inhibits murine spleen cell mitogen responses, including a depression of 3H-thymidine incorpora- tion induced by T cell mitogens phytohemagglutinin (PHA) and concanavalin A (Con A) (Ward et al., 1986). The ability of cytotoxic T lymphocytes to kill target cells is inhibited by DMBA following in vivo or in vitro exposure (House et al., 1987, 1989). DMBA is also known to inhibit the production of IL-2 by murine splenic T cells (House et al., 1987). Due to the complexity of the immune system, it is difficult to characterize the mechanisms of xenobiotic-induced immunotoxicity using hetero- geneous cell populations obtained from lymphoid tissues and organs. Therefore, the purpose of these studies was to examine an in vitro model for the effects of DMBA on human T lymphocytes. Jurkat is a cloned human T cell leukemia cell line that has proved to be very useful in immunology studies of T cell activation and signal transduction mechanisms (Imboden, Weiss & Stobo, 1985; Rabinovitch, June, Grossman & Ledbetter, 1986). Since Ca ~2 plays an important role in cell activation and intracellular signaling (Weiss, Imboden, Hardy, Manger, Terhorst *A preliminary report of the results of these studies was February, 1988. tAuthor to whom correspondence should be addressed. presented at the 21st Meeting of The Society of Toxicology, 109