Effect of Cigarette Smoke on Autoimmunity in Murine and Human Systemic Lupus Erythematosus

Several studies have found that smoking cigarettes is a risk factor for systemic lupus erythematosus (SLE). To examine this issue in a mouse model, we subjected pre-autoimmune MRL-lpr/lpr mice for 4 weeks to cigarette smoke to provide standardized smoke effluents equivalent to moderate or to heavy smoking habits for people. The spontaneous production of IgG anti-chromatin but not IgM anti-chromatin, anti-denatured DNA, or rheumatoid factor antibodies was lower in mice exposed to 250 mg/m3 particulates from mainstream smoke, and this suppression of autoimmunity was sustained for 8 weeks (p < 0.02). In contrast to control mice anti-chromatin activity in smoke-exposed mice began to increase in 16-week-old mice, reaching levels at 6 months that were two- to three-fold higher than controls for IgG (p < 0.03) and 10-fold higher for IgM (p < 0.001). There was no significant effect on total IgG or IgM. In newly diagnosed SLE patients, smoking was negatively correlated with IgG anti-DNA antibodies (p < 0.03). However, of nine patients who discontinued smoking prior to diagnosis, eight had elevated IgG anti-DNA compared to 29/79 never smokers and 9/31 smokers (p < 0.01 compared to former smokers). Inhaled cigarette smoke appears to have a long-lasting immunosuppressive effect on T-cell-dependent autoimmune responses, although autoantibodies increase to supra-elevated levels after the suppressive effect has abated.

Cytochrome P450 1B1 Is Required for 7,12-Dimethylbenz(a)-anthracene (DMBA) Induced Spleen Cell Immunotoxicity

7,12-Dimethylbenz(a)anthracene (DMBA) is a potent carcinogen that induces immunosuppression of both humoral and cell-mediated immunity in mice and other species. Previous studies have shown that CYP1B1 is required for bone marrow toxicity produced by DMBA in mice. Therefore, the purpose of these studies was to determine whether CYP1B1 was required for spleen cell immunotoxicity. Female C57BL/6N wild-type (WT) and CYP1B1 knockout (-/-) mice were treated with 0, 17, 50, or 150 mg/kg (cumulative dose) DMBA in corn oil by oral gavage once a day for five days. Several immunotoxicological assays were used to assess the effects of DMBA on systemic immunity. These included the in vitro T-dependent antibody response to sheep red blood cells (SRBC) measured using a direct plaque forming cell (PFC) assay, T- and B-cell mitogenesis induced by Con A and LPS, and nonspecific cell-mediated immunity was evaluated using an NK cytotoxicity assay. In addition, lymphocyte subpopulations were measured by flow cytometry using specific cell surface markers. Following five days of DMBA treatment, the body weights and spleen cell surface markers of the WT and CYP1B1 (-/-) mice showed no significant changes. A decrease in NK activity was found at the 50 mg/kg DMBA dose in WT mice, but not in the CYP1B1 (-/-) mice. Interestingly, at the 150 mg/kg dose of DMBA, CYP1B1 null mice had decreased NK activity, whereas WT mice did not. The SRBC PFC response demonstrated that the IgM antibody response was suppressed by DMBA in WT mice in a dose-dependent manner (significant at 50 and 150 mg/kg). However, there were no changes in the SRBC PFC responses in any DMBA test group in the CYP1B1 (-/-) mice. Similarly, while DMBA suppressed B- and T-cell mitogenesis at the 50 and 150 mg/kg dose levels in C57BL/6N WT mice, no effect was seen in CYP1B1 (-/-) mice. Thus, CYP1B1 appears to be critical for the immunosuppression of DMBA in mice, suggesting a role for bioreactive metabolites in the spleen cell immunotoxicity produced by DMBA.

Hardwood smoke alters murine splenic T cell responses to mitogens following a 6-month whole body inhalation exposure

The purpose of these studies was to assess the effects of hardwood smoke (HWS) inhalation (30-1000 microg/m3) on the systemic immune responses of A/J mice evaluated after 6 months of daily exposures. Spleen cells obtained from mice were assessed for changes in cell number, cell surface marker expression [B, T, macrophage, and natural killer (NK) cells], and responses to B cell (LPS, endotoxin) and T cell (Con A) mitogens. Results showed that HWS smoke increased T cell proliferation in the 100 microg/m3 exposure group and produced a concentration-dependent suppression of T cell proliferation at concentrations >300 microg/m3. There were no effects on B cell proliferation or in spleen cell surface marker expression. Analyses of the exposure atmospheres revealed the presence of significant levels of naphthalene and methylated napthalenes, fluorene, phenanthrene, and anthracene in the exposure chambers, as well as low concentrations of several metals (K, Ca, and Fe). Our results demonstrate that environmentally relevant concentrations of HWS may be immunosuppressive to the immune system of mice exposed during a 6-month period.

Systemic immunotoxicity in AJ mice following 6-month whole body inhalation exposure to diesel exhaust

The purpose of these studies was to determine the effects of subchronic diesel exposure on indicators of systemic immunity in mice. AJ mice were exposed daily for 6 months (6 h/day) to atmospheres containing one of four concentrations (30, 100, 300, and 1000 microg/m(3)) of diluted diesel exhaust (DE) in whole body exposure chambers. The effects of DE were compared to chamber exposure controls receiving fresh air. DE was assessed for effects on systemic immunity by measuring the proliferative response of spleen cells following stimulation with T cell (phytohemagglutinin, or PHA) or B cell (lipopolysaccharide, or LPS) mitogens. The results showed that DE at all exposure levels suppressed the proliferative response of T cells. B cell proliferation was increased at 30 microg/m(3) and was unaffected at the 100, 300, and 1000 microg/m(3) exposures. Polycyclic aromatic hydrocarbons (PAHs) are known to suppress spleen cell mitogenic responses, and it has been hypothesized by several groups that PAHs and perhaps benzo(a)pyrene (BaP)-quinones (BPQs) may be responsible for the effects of DE or diesel exhaust particles (DEP). Therefore, a second purpose of these studies was to determine the effects of in vitro BPQs on AJ mouse spleen cell mitogenic responses and compare to DE in preliminary studies. Unlike DE, BPQs were found to increase T cell proliferation. In addition, analysis of chamber atmospheres showed that there was little if any PAH and BPQs in DE. Therefore, these results demonstrate that because of the absence of BPQs in DE, they are likely not responsible for the immunosuppressive effect of DE on murine spleen cell responses.

Benzo(a)pyrene quinones increase cell proliferation, generate reactive oxygen species, and transactivate the epidermal growth factor receptor in breast epithelial cells

Polycyclic aromatic hydrocarbons, such as benzo(a)pyrene (BaP), are known mammary carcinogens in rodents and may be involved in human breast cancer. We have reported previously that BaP can mimic growth factor signaling and increase cell proliferation in primary human mammary epithelial cells and the human mammary epithelial cell line MCF-10A. BaP-quinones (BPQs) are important metabolites of BaP that have been associated with the production of reactive oxygen species. Using a model of epidermal growth factor (EGF) withdrawal in MCF-10A, we hypothesized that production of reactive oxygen species by BPQs could lead to the activation of the EGF receptor (EGFR). Here, we demonstrate through electron paramagnetic resonance spectroscopy and flow cytometry that 1,6-BPQ and 3,6-BPQ produce superoxide anion and hydrogen peroxide in MCF-10A cells. Furthermore, we show that BPQs increase EGFR, Akt, and extracellular signal-regulated kinase activity, leading to increased cell number in the absence of EGF. The BPQ-induced EGFR activity and associated cell proliferation were attenuated by the EGFR inhibitor AG1478, as well as by the antioxidant N-acetyl cysteine. Overexpression of catalase, but not Cu/Zn superoxide dismutase, reduced the extent of BPQ-dependent increased cell number and EGFR pathway activation. Moreover, the direct treatment of MCF-10A cells with hydrogen peroxide enhanced EGFR, Akt, and extracellular-regulated kinase phosphorylation that could be similarly inhibited by AG1478, N-acetyl cysteine, and catalase. Taken together, these data indicate that BPQs, through the generation of hydrogen peroxide, activate the EGFR in MCF-10A cells, leading to increased cell number under EGF-deficient conditions.

Aryl hydrocarbon receptor-mediated activity of particulate organic matter from the Paso del Norte airshed along the U.S.-Mexico border

In this study, we determined the biologic activity of dichloromethane-extracted particulate matter < 10 micro m in aerodynamic diameter (PM10) obtained from filters at three sites in the Paso del Norte airshed, which includes El Paso, Texas, USA; Juarez, Chihuahua, Mexico, and Sunland Park, New Mexico, USA. The extracts were rich in polycyclic aromatic hydrocarbons (PAHs) and had significant biologic activity, measured using two in vitro assay systems: ethoxyresorufin-(O-deethylase (EROD) induction and the aryl hydrocarbon-receptor luciferase reporter system. In most cases, both EROD (5.25 pmol/min/mg protein) and luciferase activities (994 relative light units/mg) were highest in extracts from the Advance site located in an industrial neighborhood in Juarez. These values represented 58% and 55%, respectively, of induction associated with 1 micro M ss-naphthoflavone exposures. In contrast, little activity was observed at the Northeast Clinic site in El Paso, the reference site. In most cases, luciferase and EROD activity from extracts collected from the Tillman Health Center site, situated in downtown El Paso, fell between those observed at the other two sites. Overall, a statistically significant correlation existed between PM10 and EROD and luciferase activities. Chemical analysis of extracts collected from the Advance site demonstrated that concentrations of most PAHs were higher than those reported in most other metropolitan areas in the United States. Calculations made with these data suggest a cancer risk of 5-12 cases per 100,000 people. This risk estimate, as well as comparisons with the work of other investigators, raises concern regarding the potential for adverse health effects to the residents of this airshed. Further work is needed to understand the sources, exposure, and effects of PM10 and particulate organic material in the Paso del Norte airshed.

The aryl hydrocarbon receptor antagonist, 3'methoxy-4'nitroflavone, attenuates 2,3,7,8-tetrachlorodibenzo-p-dioxin-dependent regulation of growth factor signaling and apoptosis in the MCF-10A cell line

Previous studies have demonstrated that 2,3,7,8 tetracholorodibenzo-p-dioxin (TCDD) mimics epidermal growth factor receptor (EGFR) signaling in the MCF-10A human mammary epithelial cell line and protects cells from EGF withdrawal-induced apoptosis. These effects appear to be due to the ability of TCDD to increase the expression of transforming growth factor-alpha (TGFalpha), a known EGFR ligand. Because TCDD's effects occurred at concentrations as low as 1 nM, a role for the aryl hydrocarbon receptor (AhR) was hypothesized. In the present study, 3'methoxy-4'nitroflavone (MNF), a known AhR antagonist, was used to analyze AhR signaling in this cell line. MNF suppressed TCDD-dependent dioxin response element (DRE)-driven luciferase activity at concentrations as low as 10 nM. In addition, MNF attenuated TCDD's ability to inhibit apoptosis and to activate Akt and Erk1,2, two EGFR-dependent signaling molecules. Finally, the TCDD-dependent increase in TGFalpha mRNA was also suppressed by MNF. MNF's effects on TCDD action in the MCF-10A cell line occurred at concentrations ranging from 1 nM for Akt phosphorylation and TGFalpha expression to 100 nM for inhibition of apoptosis. Attenuation of TCDD-dependent luciferase activity occurred at concentrations as low as 10 nM, which suggests that TCDD inhibits apoptosis in human mammary epithelial cells by multiple mechanisms.

Environmental polycyclic aromatic hydrocarbons, benzo(a) pyrene (BaP) and BaP-quinones, enhance IgE-mediated histamine release and IL-4 production in human basophils

Polycyclic aromatic hydrocarbons (PAHs) are major components of diesel exhaust particles found in pollutant respirable particles. There is growing evidence that these fossil fuel combustion products exacerbate allergic inflammation. Basophils contribute to allergic inflammation through the release of preformed and granule-derived mediators. To determine whether allergens and PAHs interact, we incubated human basophils with PAHs and measured the release of histamine and IL-4 with and without added antigen. None of the PAHs induced mediator release by itself and none affected total cellular histamine levels. However, several PAHs enhanced histamine release and IL-4 production in response to crosslinking the high-affinity IgE receptor, Fc epsilon RI. The enhancement seen with 1,6-BaP-quinone involved an increase in tyrosine phosphorylation in several different substrates, including the Fc epsilon RI-associated tyrosine kinase, Lyn, and elevated reactive oxygen species (ROS) levels detected by dichlorofluorescein fluorescence and flow cytometry. The PAH-induced enhancement of mediator release and ROS production could be inhibited with the antioxidant N-acetylcysteine. These data provide further evidence that environmental pollutants can influence allergic inflammation through enhanced Fc epsilon RI-coupled mediator release from human basophils.

3-methylindole-induced toxicity to human bronchial epithelial cell lines

Transfected BEAS-2B cells that express different cytochrome P450 enzymes were used to assess whether human bronchial epithelial cell lines are target cells for 3-methylindole (3MI)-induced damage. Four different transfected BEAS-2B lines overexpressing P450s 2A6, 3A4, 2F1, and 2E1 (B-CMV2A6, B-CMV3A4, B-CMV2F1, and B-CMV2E1), respectively, were compared. The B-CMV2F1 and B-CMV3A4 cells were the most susceptible to 3MI-mediated cytotoxicity, measured by leakage of lactate dehydrogenase into the medium after a 48-h incubation. The toxicity was ameliorated by pretreatment with 1-aminobenzotriazole (ABT). Depletion of glutathione with diethylmaleate decreased the onset and increased the extent of cell death with 3MI. Thus, 3MI is cytotoxic to immortalized bronchial epithelial cells overexpressing 2F1 without concomitant depletion of GSH, but depletion of GSH modestly enhances the cytotoxicity of 3MI to human lung cells. Additional studies clearly demonstrated that a low concentration of 3MI (10 micro M) induced apoptosis in BEAS-2B cells that was measured by DNA fragmentation, and apoptosis was inhibited by the presence of ABT. The B-CMV2F1 cells overexpressing 2F1 demonstrated increased apoptosis (measured by Annexin-V binding) at 24 h with 100 micro M 3MI. Therefore, CYP2F1 in human bronchial epithelial lung cells may bioactivate 3MI to 3-methyleneindolenine, which induces programmed cell death at relatively low concentrations. Human lung cells may be susceptible to this prototypical pneumotoxicant.

Determining the site of spin trapping of the equine myoglobin radical by combined use of EPR, electrophoretic purification, and mass spectrometry

Although myoglobin protein radicals are thought important intermediates in peroxide-induced toxicity, the site of spin trapping of this radical in equine myoglobin using the trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) is unclear. We have combined EPR, electrophoretic adduct purification, and mass spectrometry approaches to unambiguously determine the site of trapping to be Tyr-103 and suggest that reports of trapping at Trp-7 or Trp-14 may be due to nonradical addition to proteolytically derived Trp-containing peptides with DBNBS. The technique developed here of combining electrophoretic separation of DBNBS adducts with MS of resultant peptides will also allow proteomic-like approaches to determining identities and sites of radical formation and translocation on complex mixtures of proteins.

Prevention of apoptosis by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the MCF-10A cell line: correlation with increased transforming growth factor alpha production

We have recently reported that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inhibits epidermal growth factor (EGF) withdrawal-induced apoptosis in the human mammary epithelial cell line MCF-10A. We hypothesized that TCDD-mediated inhibition of apoptosis was due to its ability to stimulate the EGF receptor (EGFR) pathway. Indeed, in the present studies, the EGFR inhibitor AG1478 was able to prevent TCDD-, EGF-, and transforming growth factor alpha (TGF-alpha)-dependent cell recovery and inhibition of apoptosis. These effects were specific for an EGFR-mediated pathway because cotreatment with AG825, an erbB2 inhibitor, had little effect on apoptosis. In addition, TCDD was able to mimic the EGF and TGF-alpha signaling as demonstrated by increasing Akt and extracellular signal-regulated kinase 1,2 phosphorylation. These effects were dependent on EGFR activity because AG1478, but not AG825, was able to prevent EGF-, TGF-alpha, or TCDD-mediated Akt and extracellular signal-regulated kinase 1,2 phosphorylation. The ability of TCDD to stimulate the EGFR pathway and inhibit apoptosis may be due to the ability of TCDD to increase expression of TGF-alpha, a ligand for EGFR. Treatment with 10 nM TCDD increased TGF-alpha mRNA at 2 h and TGF-alpha protein at 6 h. These data suggest a mechanism whereby TCDD is able to inhibit apoptosis in human mammary epithelial cells by stimulating TGF-alpha production, resulting in an autocrine effect.

A bioactive metabolite of benzo[a]pyrene, benzo[a]pyrene-7,8-dione, selectively alters microsomal Ca2+ transport and ryanodine receptor function

Polycyclic aromatic hydrocarbons are environmental pollutants known to be carcinogenic and immunotoxic. In intact cell assays, benzo[a]pyrene (B[a]P) disrupts Ca(2+) homeostasis in both immune and nonimmune cells, but the molecular mechanism is undefined. In this study, B[a]P and five metabolites are examined for their ability to alter Ca(2+) transport across microsomal membranes. Using a well-defined model system, junctional SR vesicles from skeletal muscle, we show that a single o-quinone metabolite of B[a]P, B[a]P-7,8-dione, can account for altered Ca(2+) transport across microsomal membranes. B[a]P-7,8-dione induces net Ca(2+) release from actively loaded vesicles in a dose-, time-, and Ca(2+)-dependent manner. In the presence of 5 microM extravesicular Ca(2+), B[a]P-7,8-dione exhibited threshold and EC(50) values of 0.4 and 2 microM, respectively, and a maximal release rate of 2 micromol of Ca(2+) min(-1) mg(-1). The mechanism by which B[a]P-7,8-dione enhanced Ca(2+) efflux was further investigated by measuring macroscopic fluxes and single RyR1 channels reconstituted in bilayer lipid membranes and direct measurements of SERCA catalytic activity. B[a]P-7,8-dione (< or = 20 microM) had no measurable effect on initial rates of Ca(2+) accumulation in the presence of ruthenium red to block ryanodine receptor (RyR1), nor did it alter Ca(2+)-dependent (thapsigargin-sensitive) ATPase activity. B[a]P-7,8-dione selectively altered the function of RyR1 in a time-dependent diphasic manner, first activating then inhibiting channel activity. Considering that RyR1 and its two alternate isoforms are broadly expressed in mammalian cells and their important role in Ca(2+)-signaling, the present results reveal a mechanism by which metabolic bioactivation of B[a]P may mediate RyR dysfunction of pathophysiological significance.

Analysis of genetic and epigenetic mechanisms of toxicity: potential roles of toxicogenomics and proteomics in toxicology

The article highlighted in this issue is "An Aryl Hydrocarbon Receptor Independent Mechanism of JP-8 Jet Fuel Immunotoxicity in Ah-Responsive and Ah-Nonresponsive Mice" by Andrew C. Dudley, Margie M. Peden-Adams, Jackie EuDaly, Richard S. Pollenz, and Deborah E. Keil (pp. 251-259).

Signaling by environmental polycyclic aromatic hydrocarbons in human lymphocytes

During the past decade there has been significant progress made in understanding how environmental agents, drugs, certain chemicals present in the diet, and occupational agents affect the immune system of animals and humans. Polycyclic aromatic hydrocarbons (PAHs) are an important class of environmentally prevalent xenobiotics that exert complex effects on the immune system. These agents, typified by benzo(a)pyrene (BaP), have been shown to alter antigen and mitogen receptor signaling pathways, leading to suppression of humoral and cell-mediated immunity, and at high exposure levels to activation of genes involved in apoptosis in lymphoid cells. Interestingly, at low exposure levels, PAHs may actually augment cell signaling pathways, resulting in immune enhancement or an adjuvant effect. While the biochemical targets and mechanisms responsible for immune modulation are still under investigation, several themes are evolving. PAHs, principally through their cytochrome-P450-derived metabolites, activate oxidative and electrophilic signaling pathways in lymphoid and nonlymphoid cells, including myeloid, epithelial, and other cells. Although PAHs affect signaling pathways in nonlymphoid cells leading to complex interactions between antigen-specific and nonspecific immune and inflammatory responses, this brief review focuses on the mechanisms of signaling by environmentally prevalent PAHs in human lymphocytes. Understanding the mechanisms by which xenobiotics alter adaptive and nonadaptive immune responses may shed light on the etiology of environmental and occupational immune diseases.

Interactions between benzo[a]pyrene and UVA light affecting ATP levels, cytoskeletal organization, and resistance to trypsinization

Polycyclic aromatic hydrocarbons affect cells in many ways, including covalent modifications of DNA, participation in redox cycling, and alterations in cellular signaling pathways. Similarly, exposure to ultraviolet (UV) light may modify DNA, generate reactive oxygen species, and alter signaling. Because environmental conditions may interact to affect cellular functions, we investigated the combined effects of benzo[a]pyrene (BaP) and UV light in a cell line in which BaP-induced alterations in Ca(2+) homeostasis have previously been shown. Exposure of MCF-10A cells to BaP (18 h) followed by a brief (5 min) exposure to UVA resulted in resistance to trypsinization of cells grown on type I collagen (Vitrogen). This effect was not seen following treatment with BaP or UVA alone nor with benzo(e)pyrene (BeP)+UVA. BaP+UVA light also caused actin filaments to reorganize from typical stress fibers to substrate-associated aggregates of actin and caused depletion of cellular adenosine triphosphate (ATP). The effects of BaP+UVA on adhesion and actin aggregate formation were partially prevented by treatment with reduced glutathione. Depletion of cellular ATP affected resistance to trypsinization and actin organization in a similar manner. Thus, these studies suggest a redox-sensitive interaction between BaP+UVA light to deplete cellular ATP levels, resulting in resistance to trypsinization and actin filament reorganization in MCF-10A cells.

Analysis of free intracellular calcium by flow cytometry: multiparameter and pharmacologic applications

Flow cytometry offers numerous advantages over traditional techniques for measuring intracellular Ca(2+) in lymphoid and nonlymphoid cells. In particular, the heterogeneity of cell responses can be defined by flow cytometry, and multiparameter analyses permit the determination of intracellular Ca(2+) in surface-marker-defined target cells as well as correlation of changes in Ca(2+) with other biochemical markers, including ligand binding. This article presents several established methods for measuring intracellular Ca(2+) by flow cytometry in lymphoid and nonlymphoid cells. Examples are provided for determination of Ca(2+) in human peripheral blood leukocytes and two human epithelial cell lines grown in monolayer. In addition, applications are reviewed or presented for correlating changes in intracellular Ca(2+) with other cell parameters, including cell cycle analysis, changes in cell membrane integrity, and the induction of apoptosis markers. Finally, a number of novel sample handling capabilities useful for performing kinetic analyses of Ca(2+) changes by flow cytometry are now available and one application is presented which is finding utility in pharmacologic studies.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) inhibits growth factor withdrawal-induced apoptosis in the human mammary epithelial cell line, MCF-10A

Previous studies have demonstrated that 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) increases cell recovery in the human mammary epithelial cell line MCF-10A grown under growth factor-restricted conditions. TCDD was also found to mimic growth factor signaling pathways by stimulating the tyrosine phosphorylation of numerous effector molecules, and increased phosphatidylinositol 3-kinase (PI3K) activity in the absence of exogenously added growth factors. In the present studies, we have expanded on these initial results to show that TCDD (3-30 nM) increases cell recovery on days 2-6 by as much as 80% when insulin or epidermal growth factor (EGF) was removed from the media. The mechanism for this effect appears to be complex as TCDD inhibited apoptosis stimulated by EGF, or EGF and insulin, withdrawal by almost 80% as determined by Annexin V binding. However, withdrawal of insulin alone did not induce apoptosis even though TCDD did increase cell number in its absence. These results were corroborated by immunoblot analysis of poly(ADP-ribose) polymerase cleavage. Since TCDD stimulates PI3K activity, the phosphorylation status of Akt, a serine/threonine kinase that mediates PI3K-dependent inhibition of apoptosis, was examined. Immunoblot analysis revealed that TCDD causes a transient increase in the phosphorylated form of Akt that peaks at 6 h and disappears by 12 h. It appears that EGF stimulates an anti-apoptotic pathway, while insulin signals a pro-mitogenic pathway. By stimulating or mimicking one or both of these pathways TCDD may alter tightly regulated growth pathways in the MCF-10A cell line.

Uses and future applications of flow cytometry in immunotoxicity testing

Flow cytometry is an emerging technology that has numerous applications to immunotoxicity testing. The use and development of high-speed single-cell laser-based assays capable of quantitation of fluorescence, light scatter, and electrical impedance measurements can provide important information on xenobiotic-induced toxicity in defined target cell populations. The purpose of this article is to briefly review established and emerging immunotoxicology assays that use flow cytometry. In the coming years it is likely that many new flow cytometry assays will be developed and validated that will improve the sensitivity and perhaps specificity of immunotoxicity testing. Since flow cytometry is readily adaptable to high-throughput screening, it is also likely that this technology will increasingly find its place in the preclinical testing of drugs and chemicals in the pharmaceutical and chemical industries.

Factors influencing elevation of intracellular Ca2+ in the MCF-10A human mammary epithelial cell line by carcinogenic polycyclic aromatic hydrocarbons

Carcinogenic polycyclic aromatic hydrocarbons and a halogenated aromatic hydrocarbon, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), were evaluated for their effects on intracellular Ca2+ in the human mammary epithelial cell line MCF-10A. After two 18-h incubations with MCF-10A cells, benzo[a]pyrene (BaP; 1, 3, and 10 microM) produced a dose-dependent increase in intracellular Ca2+. 7,12-Dimethylbenz[a]anthracene increased Ca2+ at 10 microM, whereas 3-methylcholanthrene and TCDD did not. The Ca2+-elevating effect of BaP appeared to be dependent on the influx of extracellular Ca2+, as addition of the Ca2+ chelator EGTA to the extracellular medium prevented the increase in Ca2+. MCF-10A cells were found by polymerase chain reaction to express cytochrome P4501A and P4501B isozymes as well as the aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator mRNAs associated with cytochrome P450 induction. Certain cytochrome P450-derived metabolites, including benzo[a]pyrene-7,8-diol (BP-diol) and benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), were more effective in increasing Ca2+ than was BaP. The Ca2+-elevating effect of BP-diol was prevented by alpha-naphthoflavone, a cytochrome P4501A and P4501B inhibitor, but not by the antioxidant N-acetylcysteine. These results suggest that cytochrome P450-dependent formation of BPDE from BP-diol is a major mechanism required for elevation of Ca2+ in MCF-10A cells.

Protein tyrosine kinase activation by polycyclic aromatic hydrocarbons in human HPB-ALL T cells

It has been well established that certain polycyclic aromatic hydrocarbons (PAHs), such as 7,12-dimethylbenz[a]anthracene (DMBA), 3-methylcholanthrene (3MC), and benzo[a]pyrene (BaP), produce immunotoxicity and cancer in rodents and that these effects are also likely seen in humans. Our laboratory has found that polycyclic aromatic hydrocarbons (PAHs) produce an increase in intracellular Ca2+ in lymphocytes that appears to correlate with their immunotoxicity. Specifically, immunotoxic PAHs, such as DMBA and BaP, have been shown to produce a sustained increase in intracellular Ca2+ in lymphocytes, whereas nonimmunosuppressive PAHs, such as benzo[e]pyrene (BeP) and anthracene, do not. Our studies previously demonstrated that the rapid increase in intracellular Ca2+ produced by DMBA in HPB-ALL T cells was caused by protein tyrosine kinase (PTK) activation in human T cells, leading to tyrosine phosphorylation of phospholipase C (PLCgamma) and IP3-dependent Ca2+ mobilization. However, the specificity of PTK activation by PAHs was not established. In the present studies, we extend our observations of PTK activation by examining a number of PAHs for their effects on total and specific (Fyn and ZAP-70) PTK activity. We show that 10 microM concentrations of PAHs nonspecifically and rapidly (within 5 min) stimulate PTKs in the HPB-ALL human T cell line. BeP and anthracene were found to be nearly as effective at increasing total tyrosine kinase activity as DMBA, 3MC, and BaP, observed 5 min after exposure. We found that only immunotoxic PAHs activated the Fyn and ZAP-70 PTKs at 10 min, but total PTK activity was still increased by nonimmunotoxic PAHs, BeP, or anthracene after 10 min of exposure. These studies demonstrate that immunotoxic PAHs increase total and specific PTK activity in the human HPB-ALL T cell line. Thus the rapid increase in PTK activity produced by PAHs may not correlate with the immunotoxicity of these agents.

Apoptosis in Daudi human B cells in response to benzo[a]pyrene and benzo[a]pyrene-7,8-dihydrodiol

Numerous studies have demonstrated an association between polycyclic aromatic hydrocarbons (PAHs) and lymphocyte toxicity. The present study shows that, consistent with its effects on Ca2+ homeostasis, benzo[a]pyrene (BaP) induces apoptosis in Daudi cells. Terminal deoxynucleotidal transferase-mediated dUTP-biotin nick end labeling (TUNEL) analysis at 18 h revealed a significant increase in the number of cells undergoing apoptosis in response to BaP (75%), BaP-7, 8-dihydrodiol (110%), and BaP-7,8-9,10-diol epoxide (BPDE) (215%) over DMSO vehicle control cultures. By 36 h, the trend toward increasing numbers of apoptotic cells continued with the parent compound producing a 125% increase over control values and the 7, 8-dihydrodiol and BPDE metabolites producing 195% and 370% increases over controls, respectively. DNA fragmentation assays demonstrated the presence of internucleosomal cleavage products consistent with the increasing numbers of TUNEL-positive cells responding to PAHs at 18 and 36 h. Analysis of poly(ADP-ribose) polymerase (PARP) protein in BaP- and BaP-7,8-dihydrodiol-treated cells strongly suggested the involvement of cysteine proteases by the appearance of an 85-kD fragment derived from hydrolytic cleavage of PARP, a phenomenon that has been associated with apoptosis in many systems. Immunoblot analysis demonstrated that both BaP and its 7,8-dihydrodiol metabolite affected a pathway involving Bcl-2 and Bax cytosolic proteins. Daudi cells undergoing apoptosis at 36 h in response to 10 microM BaP, the parent compound, expressed moderately reduced amounts of Bcl-2 (78% of vehicle controls). At the same time point, the 7,8-dihydrodiol and BDPE metabolites at 3 microM resulted in Bcl-2 protein expression that was 52% of that seen in vehicle controls. Parallel samples analyzed for expression of Bax protein displayed a 130% increase over vehicle control in Bax expression in response to the parent compound, while the 7,8-dihydrodiol metabolite produced a 257% increase in Bax. Furthermore, the effects on increased Bax expression were observed as early as 3 h after PAH exposure. The apoptotic response to PAHs in Daudi cells was sensitive to 4-h pretreatment with 0.3 microM alpha-naphthoflavone (ANF), a known inhibitor of cytochrome P450. In TUNEL assays of cells exposed to PAHs following pretreatment with ANF, at 18 h there was a significant reduction in the number of cells undergoing apoptosis in response to ANF compared to cells that were not pretreated with the compound. The effect of the parent compound at 18 h was completely blocked with ANF pretreatment, while ANF exerted a relatively weaker, but significant, effect on BaP-7, 8-dihydrodiol-induced apoptosis. With regard to modulation of expression of apoptosis-related proteins, Bax expression was restored to that observed in vehicle-control cultures at all time points tested (3, 18, and 36 h). Bcl-2 expression was most responsive to ANF at later time points following PAH exposure (18 and 36 h); however, Bcl-2 appeared to be more sensitive to the effects of ANF alone. Taken together, these data suggest that modulation of Bcl-2 family proteins, perhaps secondary to altered Ca2+ homeostasis, plays an important role in human B cell apoptosis induced by BaP.

Benzo[a]pyrene- and TCDD-induced alterations in tyrosine phosphorylation and insulin-like growth factor signaling pathways in the MCF-10A human mammary epithelial cell line

Previous studies in this laboratory have shown that polycyclic aromatic hydrocarbons, such as benzo[a]pyrene (BaP), and certain halogenated aromatic hydrocarbons, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), modulate receptor signaling pathways in human lymphoid and non-lymphoid cells. We have recently demonstrated that BaP produces a weak mitogenic signal in human mammary epithelial cells, perhaps by mimicking growth factor signaling pathways. In the present studies we found that BaP and TCDD activated insulin-like growth factor (IGF-I) signaling pathways under insulin-deficient conditions. The effects of BaP and TCDD were evaluated in the human MCF-10A mammary epithelial cell line grown under epidermal growth factor- and insulin-dependent conditions. BaP (0.3 microM) and TCDD (30 nM) were found to restore a moderate insulin-like signal in MCF-10A cells grown in the absence of added insulin. TCDD was more potent and produced better activation of cell growth than did BaP. Both TCDD and BaP appeared to mimic signaling through the IGF-I receptor (IGF-IR), as evidenced by increased tyrosine phosphophorylation of IGF-IRbeta, IRS-1 and Shc. In addition, both BaP and TCDD significantly increased the activity of phosphatidylinositol 3-kinase (PI3K). The PI3K inhibitor LY294002 was found to inhibit the growth-promoting effects of TCDD seen under insulin-deficient conditions. The results of these studies show that under certain conditions BaP and TCDD can mimic growth factor signaling pathways in human mammary epithelial cells, demonstrating that environmentally prevalent carcinogenic compounds may alter cell growth in human mammary epithelial cells via mimicry of growth factor receptor signaling pathways.

Alterations in human B cell calcium homeostasis by polycyclic aromatic hydrocarbons: possible associations with cytochrome P450 metabolism and increased protein tyrosine phosphorylation

Previous studies performed in this laboratory have shown that certain benzo(a)pyrene (BaP) metabolites, such as benzo(a)pyrene-7,8-dihydrodiol (BaP-7,8-diol) and benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), were more effective in elevating intracellular Ca2+ in normal human peripheral blood mononuclear cell (HPBMC) T and B cells than was BaP. Additionally, it has been shown that the suppression of human T cell mitogenesis produced by polycyclic aromatic hydrocarbons (PAHs) and certain BaP metabolites is reversed by treatment with alpha-naphthoflavone (ANF), a cytochrome P450 1A and 1B inhibitor. ANF also diminishes the elevation in intracellular calcium (Ca2+) produced by BaP in HPBMC. In the present studies, we further defined the relationships between intracellular Ca2+ elevation produced by BaP and two immunotoxic P450-derived metabolites, BaP-7,8-diol and BPDE in the Daudi human B cell line. At 1, 4, and 18 h, both BaP-7,8-diol and BPDE produced a significant rise in intracellular Ca2+. This effect, however, was not observed with BaP or benzo(e)pyrene (BeP), a nonimmunotoxic PAH. To evaluate the potential role of cytochrome P450 metabolism in PAH-induced Ca2+ elevation, Daudi cells were pretreated with ANF for 4 h, followed by treatment with BaP metabolites for 18 h. ANF completely reversed the rise in Ca2+ produced by BaP-7,8-diol, but had no effect on the Ca2+ elevation produced by BPDE. These results suggest that BPDE may be the ultimate P450 metabolite responsible for Ca2+ elevation in human B cells. BaP-7,8-diol and BPDE were found to increase tyrosine phosphorylation in Daudi whole cell lysates and to increase tyrosine phosphorylation of two important Src-related protein tyrosine kinases (PTKs), Lyn and Syk. Inhibition of tyrosine phosphorylation by herbimycin A was found to largely prevent the increase in intracellular Ca2+ produced by BaP-7,8-diol and BPDE, suggesting that Ca2+ elevation is coupled to increased tyrosine phosphorylation in Daudi. BPDE was found to produce a statistically significant increase in tyrosine phosphorylation of Lyn and Syk within 10 min of exposure. Collectively, these data demonstrate that certain P450-derived metabolites of BaP may be responsible for PTK activation and an increase intracellular Ca2+, which may alter antigen receptor signaling in human B cells.

Characterization of intracellular calcium responses produced by polycyclic aromatic hydrocarbons in surface marker-defined human peripheral blood mononuclear cells

Previous studies have demonstrated that polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene (BaP) and 7,12-dimethybenz[a]anthracene (DMBA), and possibly 2,3,7,8-tetrachlorodibenzo(p)dioxin (TCDD), may exert their immunosuppressive effects by altering intracellular Ca2+ homeostasis in lymphocytes. In these studies, we examined the effects of two immunosuppressive PAHs (BaP and DMBA), two nonimmunosuppressive PAHs (benzo[e]pyrene (BeP) and anthracene (ANTH)), and TCDD on intracellular Ca2+ levels in surface marker-defined human peripheral blood mononuclear cells (HPBMC). BaP and DMBA, but not BeP and ANTH, were found to produce a time-dependent increase in intracellular Ca2+ with maximal effects achieved following 42- to 66-hr exposures. In a series of studies with HPBMC obtained from 10 donors exposed in vitro for 42 hr, BaP and DMBA were found to produce a significant increase in Ca2+ in CD3+ T cells, CD19+ B cells, and CD14+ monocytes. BeP and ANTH did not produce a statistically significant increase in Ca2+ in the group of donors, but occasionally produced an apparent nonspecific elevation of Ca2+ in HPBMC from individual donors. Interestingly, TCDD produced a small and statistically significant increase in Ca2+ only in B cells analyzed for the pooled 10 donors. Certain BaP metabolites, such as the 7,8-dihydrodiol and the 7,8-diol-9,10-epoxide, were more effective in elevating Ca2+ in HPBMC lymphocytes at 20 hr than was BaP. These results demonstrate in normal HPBMC that immunosuppressive PAHs alter intracellular Ca2+ homeostasis in B cells, T cells, and monocytes, and suggest that P450 metabolism may play an important role in the immunotoxicity of certain PAHs.