Studies on 2,3,7,8-tetrachlorodibenzo-p-dioxin induced immune suppression and decreased resistance to infection: endotoxin hypersensitivity, serum zinc concentrations and effect of thymosin treatment

Dynamic relationship between the aryl hydrocarbon receptor and long noncoding RNA balances cellular and toxicological responses

The aryl hydrocarbon receptor (AhR) is a cytosolic transcription factor activated by endogenous ligands and xenobiotic chemicals. Once the AhR is activated, it translocates to the nucleus, dimerizes with the AhR nuclear translator (ARNT) and binds to xenobiotic response elements (XRE) to promote gene transcription, notably the cytochrome P450 CYP1A1. The AhR not only mediates the toxic effects of environmental chemicals, but also has numerous putative physiological functions. This dichotomy in AhR biology may be related to reciprocal regulation of long non-coding RNA (lncRNA). lncRNA are defined as transcripts more than 200 nucleotides in length that do not encode a protein but are implicated in many physiological processes such as cell differentiation, cell proliferation, and apoptosis. lncRNA are also linked to disease pathogenesis, particularly the development of cancer. Recent studies have revealed that AhR activation by environmental chemicals affects the expression and function of lncRNA. In this article, we provide an overview of AhR signaling pathways activated by diverse ligands and highlight key differences in the putative biological versus toxicological response of AhR activation. We also detail the functions of lncRNA and provide current data on their regulation by the AhR. Finally, we outline how overlap in function between AhR and lncRNA may be one way in which AhR can be both a regulator of endogenous functions but also a mediator of toxicological responses to environmental chemicals. Overall, more research is still needed to fully understand the dynamic interplay between the AhR and lncRNA.

TCDD exposure alters fecal IgA concentrations in male and female mice

Background

Activation of the aryl hydrocarbon receptor (AhR) can alter diurnal rhythms including those for innate lymphoid cell numbers, cytokine and hormone levels, and feeding behaviors. Because immune responses and antibody levels are modulated by exposure to AhR agonists, we hypothesized that some of the variation previously reported for the effects of AhR activation on fecal secretory immunoglobulin A (sIgA) levels could be explained by dysregulation of the diurnal sIgA rhythm.

Methods

C57Bl/6 J mice were exposed to peanut oil or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 10 or 40 μg/Kg) and fecal sIgA levels were determined in samples collected every 4 h over 4 days.

Results

Fecal sIgA concentrations were not significantly different between light and dark phases of the photoperiod in either male or female mice, and there were no significant circadian rhythms observed, but TCDD exposure significantly altered both fecal mesor sIgA and serum IgA concentrations, in parallel, in male (increased) and female (biphasic) mice.

Conclusions

AhR activation can contribute to the regulation of steady state IgA/sIgA concentrations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-022-00563-9.

The Aryl Hydrocarbon Receptor as a Modulator of Anti-viral Immunity

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, which interacts with a wide range of organic molecules of endogenous and exogenous origin, including environmental pollutants, tryptophan metabolites, and microbial metabolites. The activation of AHR by these agonists drives its translocation into the nucleus where it controls the expression of a large number of target genes that include the AHR repressor (AHRR), detoxifying monooxygenases (CYP1A1 and CYP1B1), and cytokines. Recent advances reveal that AHR signaling modulates aspects of the intrinsic, innate and adaptive immune response to diverse microorganisms. This review will focus on the increasing evidence supporting a role for AHR as a modulator of the host response to viral infection.

Pulmonary paracoccidioidomycosis in AhR deficient hosts is severe and associated with defective Treg and Th22 responses

AhR is a ligand-activated transcription factor that plays an important role in the innate and adaptive immune responses. In infection models, it has been associated with host responses that promote or inhibit disease progression. In pulmonary paracoccidioidomycosis, a primary fungal infection endemic in Latin America, immune protection is mediated by Th1/Th17 cells and disease severity with predominant Th2/Th9/Treg responses. Because of its important role at epithelial barriers, we evaluate the role of AhR in the outcome of a pulmonary model of paracoccidioidomycosis. AhR^−/− mice show increased fungal burdens, enhanced tissue pathology and mortality. During the infection, AhR^−/− mice have more pulmonary myeloid cells with activated phenotype and reduced numbers expressing indoleamine 2,3 dioxygenase 1. AhR-deficient lungs have altered production of cytokines and reduced numbers of innate lymphoid cells (NK, ILC3 and NCR IL-22). The lungs of AhR^−/− mice showed increased presence Th17 cells concomitant with reduced numbers of Th1, Th22 and Foxp3⁺ Treg cells. Furthermore, treatment of infected WT mice with an AhR-specific antagonist (CH223191) reproduced the main findings obtained in AhR^−/− mice. Collectively our data demonstrate that in pulmonary paracoccidioidomycosis AhR controls fungal burden and excessive tissue inflammation and is a possible target for antifungal therapy.

Thymosin β4: Roles in Development, Repair, and Engineering of the Cardiovascular System

The burden of cardiovascular disease is a growing worldwide issue that demands attention. While many clinical trials are ongoing to test therapies for treating the heart after myocardial infarction (MI) and heart failure, there are few options doctors able to currently give patients to repair the heart. This eventually leads to decreased ventricular contractility and increased systemic disease, including vascular disorders that could result in stroke. Small peptides such as thymosin β4 (Tβ4) are upregulated in the cardiovascular niche during fetal development and after injuries such as MI, providing increased neovasculogenesis and paracrine signals for endogenous stem cell recruitment to aid in wound repair. New research is looking into the effects of in vivo administration of Tβ4 through injections and coatings on implants, as well as its effect on cell differentiation. Results so far demonstrate Tβ4 administration leads to robust increases in angiogenesis and wound healing in the heart after MI and the brain after stroke, and can differentiate adult stem cells toward the cardiac lineage for implantation to the heart to increase contractility and survival. Future work, some of which is currently in clinical trials, will demonstrate the in vivo effect of these therapies on human patients, with the goal of helping the millions of people worldwide affected by cardiovascular disease.

New insights into the aryl hydrocarbon receptor as a modulator of host responses to infection

The host response to infection is known to be influenced by many factors, including genetics, nutritional status, age, as well as drug and chemical exposures. Recent advances reveal that the aryl hydrocarbon receptor (AhR) modulates aspects of the innate and adaptive immune response to viral, bacterial, and parasitic organisms. Although many of these observations were made using the high affinity but poorly metabolized AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), not all of the effects are detrimental to the host. Sometimes AhR activation, even with TCDD, was beneficial and improved host resistance and survival. A similar dichotomy is observed in infected AhR-deficient mice, wherein absence of functional AhR sometimes, but not always, alters host resistance. When examined in their totality, current data indicate that AhR controls multiple regulatory pathways that converge with infection-associated signals and depending on the context (e.g., type of pathogen, site of infection), lead to distinct outcomes. This creates numerous exciting opportunities to harness the immunomodulatory action of AhR to transform host responses to infection. Moreover, since many of the mechanisms cued in response to infectious agents are pivotal in the context of other diseases, there is much to be learned about AhR's cellular targets and molecular mechanisms of action.

Aryl hydrocarbon receptor (AhR) regulates silica-induced inflammation but not fibrosis

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is responsible for mediating a variety of pharmacological and toxicological effects caused by halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, recent evidence has revealed that the AhR also has numerous physiological roles aside from xenobiotic metabolism, including regulation of immune and inflammatory signaling as well as normal development and homeostasis of several organs. To investigate the role of the AhR in crystalline silica (SiO(2))-induced inflammation and fibrosis, C57Bl/6 and AhR(-/)(-) mice were exposed to SiO(2) or vehicle. Similarly, C57Bl/6 mice were exposed to SiO(2) and TCDD either simultaneously or sequentially to assess whether AhR activation alters inflammation and fibrosis. SiO(2)-induced acute lung inflammation was more severe in AhR(-)(/-) mice; however, the fibrotic response of AhR(-)(/-) mice was attenuated compared with C57Bl/6 mice. In a model of chronic SiO(2) exposure, AhR activation by TCDD in C57Bl/6 mice resulted in reduced inflammation; however, the fibrotic response was not affected. Bone marrow-derived macrophages (BMM) from AhR(-)(/-) mice also produced higher levels of cytokines and chemokines in response to SiO(2). Analysis of gene expression revealed that BMM derived from AhR(-)(/-) mice exhibit increased levels of pro-interleukin (IL)-1β, IL-6, and Bcl-2, yet decreased levels of signal transducers and activators of transcription (STAT)2, STAT5a, and serpin B2 (Pai-2) in response to SiO(2).

Beta-naphthoflavone causes an AhR-independent inhibition of invasion and intracellular multiplication of Listeria monocytogenes in murine hepatocytes

We recently reported a heretofore unknown role for the aryl hydrocarbon receptor in host resistance to listeriosis in mice. Hepatocytes are an important site for Listeria monocytogenes multiplication in vivo. In this study, we investigated whether activation of AhR in TIB73 murine embryonic hepatocytes affects the ingestion and intracellular multiplication of L. monocytogenes. Treatment of TIB73 cells with the AhR agonist beta-naphthoflavone (BNF) significantly inhibited the ingestion and intracellular growth of L. monocytogenes. The inhibitory effects of BNF were dose-dependent and correlated with up-regulation of CYP1A1. Surprisingly, pretreatment with AhR antagonists (3'-MNF or alpha-naphthoflavone) or knocking-down of AhR with siRNA did not abolish the inhibitory effects of BNF. Moreover, the inhibitory effects of BNF on invasion and intracellular growth of L. monocytogenes by BNF were observed in AhR-deficient (CRL-2710), or ARNT-dysfunctional (CRL-2717) Hepa cells. We also observed similar inhibitory effects of BNF treatment using primary hepatocytes recovered from AhR(+/-) or AhR(-/-) mice. Moreover, the prototypic AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) did not inhibit the invasion and intracellular growth of L. monocytogenes in TIB73 cells. Mechanistic studies demonstrated that ROS, but not TNF-alpha or iNOS, plays an important role in mediating BNF-induced inhibition. In conclusion, BNF caused an AhR-independent inhibition of ingestion and intracellular multiplication of L. monocytogenes in murine hepatocytes, mediated in part by production of ROS.

AHR-mediated immunomodulation: the role of altered gene transcription

The immune system is a sensitive target for aryl hydrocarbon receptor (AHR)-mediated transcriptional regulation. Most of the cells that participate in immune responses express AHR protein, and many genes involved in their responses contain multiple DRE sequences in their promoters. However, the potential involvement of many of these candidate genes in AHR-mediated immunomodulation has never been investigated. Many obstacles to understanding the transcriptional effects of AHR activation exist, owing to the complexities of pathogen-driven inflammatory and adaptive immune responses, and to the fact that activation of AHR often influences the expression of genes that are already being regulated by other transcriptional events in responding cells. Studies with TCDD as the most potent, non-metabolized AHR ligand indicate that AHR activation alters many inflammatory signals that shape the adaptive immune response, contributing to altered differentiation of antigen-specific CD4(+) T helper (TH) cells and altered adaptive immune responses. With TCDD, most adaptive immune responses are highly suppressed, which has been recently linked to the AHR-dependent induction of CD4(+)CD25(+) regulatory T cells. However activation of AHR by certain non-TCDD ligands may result in other immune outcomes, as a result of metabolism of the ligand to active metabolites or to unknown ligand-specific effects on AHR-mediated gene transcription. Based on studies using AHR(-/-) mice, evidence for a role of endogenous AHR ligands in regulation of the immune response is growing, with bilirubin and lipoxinA4 representing two promising candidates.

The aryl hydrocarbon receptor is required for optimal resistance to Listeria monocytogenes infection in mice

The aryl hydrocarbon receptor (AhR) is part of a powerful signaling system that is triggered by xenobiotic agents such as polychlorinated hydrocarbons and polycyclic aromatic hydrocarbons. Although activation of the AhR by 2,3,7,8-tetrachlorodibenzo-p-dioxin or certain polycyclic aromatic hydrocarbons can lead to immunosuppression, there is also increasing evidence that the AhR regulates certain normal developmental processes. In this study, we asked whether the AhR plays a role in host resistance using murine listeriosis as an experimental system. Our data clearly demonstrate that AhR null C57BL/6J mice (AhR(-/-)) are more susceptible to listeriosis than AhR heterozygous (AhR(+/-)) littermates when inoculated i.v. with log-phase Listeria monocytogenes. AhR(-/-) mice exhibited greater numbers of CFU of L. monocytogenes in the spleen and liver, and greater histopathological changes in the liver than AhR(+/-) mice. Serum levels of IL-6, MCP-1, IFN-gamma, and TNF-alpha were comparable between L. monocytogenes-infected AhR(-/-) and AhR(+/-) mice. Increased levels of IL-12 and IL-10 were observed in L. monocytogenes-infected AhR(-/-) mice. No significant difference was found between AhR(+/-) and AhR(-/-) macrophages ex vivo with regard to their ability to ingest and inhibit intracellular growth of L. monocytogenes. Intracellular cytokine staining of CD4(+) and CD8(+) splenocytes for IFN-gamma and TNF-alpha revealed comparable T cell-mediated responses in AhR(-/-) and AhR(+/-) mice. Previously infected AhR(-/-) and AhR(+/-) mice both exhibited enhanced resistance to reinfection with L. monocytogenes. These data provide the first evidence that AhR is required for optimal resistance but is not essential for adaptive immune response to L. monocytogenes infection.

Dioxin-induced chloracne--reconstructing the cellular and molecular mechanisms of a classic environmental disease

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is among the most toxic pollutants known to date that serves as a prototype for a group of halogenated hydrocarbon compounds characterized by extraordinary environmental persistence and unique ability to concentrate in animal and human tissues. TCDD can elicit a complex array of pleiotropic adverse effects in humans, although chloracne, a specific type of acne-like skin disease, is the only consistent manifestation of dioxin intoxication, thus representing a 'hallmark' of TCDD exposure. Chloracne is considered to be one of the most specific and sensitive biomarkers of TCDD intoxication that allows clinical and epidemiological evaluation of exposure level at threshold doses. The specific cellular and molecular mechanisms involved in pathogenesis of chloracne are still unknown. In this review, we summarize the available clinical data on chloracne and recent progress in understanding the role of the dioxin-dependent pathway in the control of gene transcription and discuss molecular and cellular events potentially involved in chloracne pathogenesis. We propose that the dioxin-induced activation of skin stem cells and a shift in differentiation commitment of their progeny may represent a major mechanism of chloracne development.

Effect of endocrine disrupting chemicals on lipopolysaccharide-induced tumor necrosis factor-alpha and nitric oxide production by mouse macrophages

Little is known about the development of infectious diseases during exposure to endocrine disrupting chemicals (EDCs), although several studies have reported on the effect of EDCs on the immune function of the human body. To assess the effect of EDCs on the development of infectious disease, we investigated the effect of eighteen possible EDCs on mouse macrophage production of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) in response to bacterial endotoxin in vitro and ex vivo. Of chemicals we examined, simazine, nitrofen, and benzyl butyl phthalate inhibited lipopolysaccharide (LPS)-induced TNF-alpha production by mouse macrophage cell line RAW 264 in vitro. Carbaryl, alachlor, nonylphenol, octylphenol, tributyltin, and triphenyltin inhibited LPS-induced NO production in vitro, whereas 2,4-dichlorophenoxy acetic acid and bisphenol A enhanced its production. Zineb and alachlor, on the other hand, enhanced LPS-induced TNF-alpha production by mouse peritoneal macrophages ex vivo, while alachlor inhibited LPS/interferon-gamma-induced NO production ex vivo. These results indicate that some EDCs exert modulatory activity on endotoxin-induced macrophage activation either positively or negatively, suggesting that these compounds may affect the development of infectious diseases. This is the first report that systematically compared the effect of EDCs on LPS action.

Immunotoxicological effects of piperine in mice

The immunotoxicological effects of piperine were investigated in Swiss male mice, gavaged at a dose of 1.12, 2.25 or 4.5 mg/kg body weight for five consecutive days. All the dose levels had no overt toxic effect and the liver gained weight normally. Treatment at highest dose, however, resulted in significant decrease in the weight of spleen, thymus and mesenteric lymph nodes, but not of peripheral lymph nodes. All the dose levels suppressed the cellular population of lymphoid organs, except for the spleen, where the doses of 1.12 and 2.25 caused an increase. Haematologically, doses of 2.25 and 4.5 mg/kg caused a significant reduction in total leucocyte counts and differential leucocyte counts showed an increase in the percentage of neutrophils. The higher doses of 2.25 and 4.5 mg/kg suppressed the mitogenic response of B-lymphocyte to lipopolysaccharide. The number of primary antibody (IgM) forming cells in the spleen and the level of primary antibody in serum, was decreased. The doses of 1.12 and 2.25 mg/kg suppressed the mitogenic response of T-lymphocytes to phytohaemagglutinin and the nitroblue tetrazolium (NBT) dye reducing activity of peritoneal exudate cells (PECs). Since the lowest dose of 1.12 mg of piperine per kg body weight had no immunotoxic effect, it may be considered as immunologically safe "no observed adverse effect level (NOAEL)" dose.

2,3,7,8-Tetrachlorodibenzo-p-dioxin is a possible activator of human cytomegalovirus replication in a human fibroblast cell line

We examined the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on human cytomegalovirus (CMV) replication in the human embryonic fibroblast cell line, MRC-5. Treatment of cells with 0.0001pg/ml TCDD augmented the cytopathic effects of CMV-infected MRC-5 cells. Moreover, TCDD increased the replication of intracellular CMV without affecting the proliferation of host cells, with a concomitant increase in CMV UL54 DNA levels. However, TCDD demonstrated no virocidal effect on cell-free CMV. Furthermore, CMV-infected MRC-5 cells expressed transcripts of the aryl hydrocarbon receptor (AhR) and AhR nuclear translocator. These results suggest that TCDD may contribute to the development of opportunistic diseases by reactivation of latently infected CMV and that TCDD regulates CMV replication through the dependence on AhR.

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on trace elements, inflammation and viral clearance in the myocardium during coxsackievirus B3 infection in mice

A myocarditic coxsackievirus B3 (CB3) infection in adult male A/J mice was used to investigate the effects of 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) exposure on mortality and on inflammatory lesion, virus and trace element contents of the heart. The mice were injected with four weekly intraperitoneal (i.p.) injections of TCDD (a loading dose of 5 microg/kg followed by three maintenance doses of 1.4 microg/kg). To reach a steady-state body burden of TCDD the mice were allowed a 90-day recovery period before infection with CB3 virus. TCDD increased the infection-induced mortality rate, whereas in TCDD-exposed mice, heart lesions at day 7 after the virus inoculation (median value 0.67% of the tissue section area; interquartile range 0.28; not statistically significant) were one-third of that in non-exposed infected mice (2.07% of the tissue section area; interquartile range 3.06). The size of the inflammatory heart lesion correlated to the amount of virus (r(s) = 0.829, P < 0.01) as well as to the calcium (Ca: r(s) = 0.725, P < 0.01) and the magnesium (Mg: r(s) = -0.615, P < 0.05) contents. In TCDD-exposed mice in situ hybridisation of viral RNA in the myocardium at day 7 showed a tendency to decreased amounts of virus, as well as a less pronounced increase in myocardial Ca content, both supporting a milder myocardial disease after TCDD exposure. No effect of TCDD exposure was seen on the zinc (Zn) or selenium (Se) levels in the myocardium. In conclusion, although TCDD seemed to have a limiting effect on viral replication and the development of the inflammatory lesion in the myocardium, mortality was increased by TCDD in this infection model. However, TCDD had no significant effects on the selected trace elements that could be of importance for the severity of the inflammatory lesion (Ca, Se), for the local host response activation (Zn) or for the development of myocardial disease complications (Mg). Accordingly, the increased mortality may be a result of an infection-induced increase in TCDD toxicity to vital organs other than the heart, and/or a TCDD-induced change in the tissue affinity and virulence of the virus, possibly causing involvement of other target organs in the infectious process and changed pathogenesis.

Development of quantitative structure-activity relationship (QSAR) models for predicting risk of exposure from carcinogens in animals

Quantitative structure-activity relationship (QSAR) models capable of predicting acute toxicity and carcinogen potency of polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated hydrocarbons, and chlorinated insecticides have been formulated. Median lethal dose (LD50) for PCDD-exposed mice correlated negatively with polarity and positively with (H acceptor x 2 chi), whereas LD50 for PCDD-exposed guinea pigs correlated with (H acceptor x density). Both (H acceptor x 2 chi) and (H acceptor x density) exhibited parabolic relationship with log P (partition coefficient). Carcinogenic potency, determined from order of magnitude (OM) values, correlated negatively with log P and positively with (length x width). Thus, a hydrophobic mechanism plays a key role in the lethal effects of PCDD in mice, whereas both hydrophobic and electronic mechanisms are involved in the lethal effects of PCDD in guinea pigs. However, the molecule's lipophilicity, length, and width may play important roles in the carcinogenic effects of chlorinated compounds.

Effects of xenobiotics on macrophage function: evaluation in vitro

Macrophages participate in a variety of inflammatory and immunologic functions (e.g., phagocytosis, cytokine production, killing of microbes and tumor cells, and processing and presentation of antigen to T lymphocytes). Because these cells are widely distributed in the circulation and throughout tissue, the effects of xenobiotics on macrophage function can be significant. Measures in vitro of altered function elicited by xenobiotic exposure can include changes in expression of cell surface proteins, in production of oxygen and nitrogen free radicals, in production of cytokines [interleukin (IL)-1, IL-6, IL-12, tumor necrosis factor alpha (TNFalpha)], in expression of adhesion molecules (ICAM-1), in phagocytosis and intracellular killing, and in antigen presentation.

A chimeric aryl hydrocarbon receptor knockout mouse model indicates that aryl hydrocarbon receptor activation in hematopoietic cells contributes to the hepatic lesions induced by 2,3,7, 8-tetrachlorodibenzo-p-dioxin

Pathologic changes associated with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) exposure have been reported in the livers of a wide range of species. While these changes have been extensively described, the mechanisms of toxic interaction(s) that produce these lesions remain unclear. Using an aryl hydrocarbon receptor (Ahr) knockout male mouse chimeric model, we investigated whether the presence of this receptor in hematopoietic and/or parenchymal cells affects TCDD-induced hepatotoxicity. Bone marrow chimeras were produced by hematopoietic reconstitution of irradiated mice. Specifically, chimeras were generated with aryl hydrocarbon receptor (AHR) positive hematopoietic and parenchymal cells (Ahr+/+ animal bone marrow cells into irradiated Ahr+/+ animals), AHR positive hematopoietic and negative parenchymal cells (Ahr+/+ into Ahr-/-), AHR negative hematopoietic and positive parenchymal cells (Ahr-/- into Ahr+/+), and AHR negative hematopoietic and parenchymal cells (Ahr-/- into Ahr-/-). Male wild-type (Ahr+/+) and knockout (Ahr-/-) animals were used as nonchimeric controls. Following TCDD treatment (30 microg/kg body wt), liver sections from mice in each control and chimeric group were histologically evaluated for necrotic and inflammatory changes. TCDD treatment produced moderate inflammation in Ahr+/+ controls and Ahr+/+ into Ahr+/+ chimeras. This response was mild in TCDD-treated Ahr-/-, Ahr-/- into Ahr-/-, Ahr+/+ into Ahr-/-, and Ahr-/- into Ahr+/+ animals and was not different from the corresponding vehicle-treated groups. Moderate necrosis was observed in all TCDD-treated controls or chimeras with AHR-positive parenchyma. No or mild necrosis was observed in TCDD- and vehicle-treated animals containing AHR-negative parenchyma. These data indicate that the presence of AHR in hepatic parenchyma alone is sufficient for TCDD induction of hepatic necrosis, and its presence in hematopoietic cells is necessary for the inflammatory response to TCDD-induced hepatic lesions.

Expression of functional aromatic hydrocarbon receptor and aromatic hydrocarbon nuclear translocator proteins in murine bone marrow stromal cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) acting through the aromatic hydrocarbon receptor (AhR) and its dimerization partner, the AhR nuclear translocator protein (arnt), elicits numerous toxicological effects including immunosuppression and thymic atrophy. Previous work has shown that TCDD alters bone marrow prothymocyte populations. These effects could be mediated at the lymphocyte level directly and/or through effects on bone marrow stromal cells, a population important in the support of lymphopoiesis. The purpose of this study was to characterize AhR and arnt expression in three murine bone marrow stromal cell lines (S17, M2-10B4, and BMS2) and in primary stromal cell cultures. Immunoblot analysis detected AhR protein in M2-10B4 and BMS2 cells. AhR protein was also detected in the primary cultures. Arnt protein could be detected in all cell cultures. Electrophoretic mobility shift assays detected TCDD-dependent dioxin-responsive element (DRE) binding in all three cell lines. DNA binding was sequence-specific and dependent on AhR, as demonstrated by the addition of unlabeled DRE DNA or of anti-AhR antibody. Results obtained with the primary cultures paralleled those seen with the stromal cell lines. The ED50 for induction of TCDD-dependent DRE binding in M2-10B4 cells was 0.21 nM. TCDD treatment did not induce stromal P4501A1 mRNA expression but did increase P4501B1 mRNA levels in all three cell lines and in the primary cultures. These results indicate that murine bone marrow stromal cells express AhR and arnt proteins. Furthermore, these proteins are functional in terms of their DRE-binding ability and potential to regulate mRNA levels in a gene-specific fashion.

Cytokines (IL-1beta and TNFalpha) in relation to biochemical and immunological effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rats

Previous studies in different strains of rats and mice have shown that the inhibition of gluconeogenesis as a result of reduced liver phosphoenolpyruvate carboxykinase (PEPCK) activity together with appetite suppression play critical roles in the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Recent immunological studies in rats demonstrated that exposure to low doses of TCDD resulted in an early and enhanced IgG response to immunization with sheep red blood cells (SRBC) and an enhanced delayed-type hypersensitivity (DTH) reaction as well as a positive popliteal lymph node (PLN) response. However, high doses of TCDD suppressed the DTH reaction. This study aimed at examining the involvement of cytokines (IL-1 and TNF) in mediating the above effects. Liver samples from a previous dose-response study on DTH reaction were investigated, in which rats were treated with TCDD (1, 3, 10, 30 and 90 microg/kg) and immunized with an antigen. mRNA levels of IL-1beta were elevated begining at the 1 microg/kg (non-lethal) dosage group with a maximum increase of about 5-fold above controls in the 90 microg/kg (lethal) dosage group. mRNA levels of TNFalpha were also significantly elevated begining at the 30 microg/kg dosage group. These results suggest that at low doses of TCDD, increased IL-1beta could be responsible for immune function stimulation, whereas at high doses of TCDD, greatly elevated TNFalpha and IL-1beta levles may exacerbate or mediate acute toxicity including immune suppression and related biochemical effects. A time course study (60 microg TCDD/kg without immunization) revealed that liver mRNA levels of TNFalpha were significantly elevated starting 24 h, and reaching a maximum 48 h after dosing with TCDD. This change was accompanied by a transient increase of mRNA levels of IL-1beta at day 4 after TCDD dosage. Thus, these data demonstrated that TCDD alone (without immunization) can cause transient increases of mRNA levels of TNFalpha and IL-1beta in liver. Results from these experiments suggest that TCDD-induced cytokine changes may play important roles in various effects of TCDD.

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on growth factor expression in the human breast cancer cell line MCF-7

The aim of this study was to examine whether changes in growth factor or cytokine expression could be responsible for the growth inhibitory effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the human breast cancer MCF-7 cell line. Treatment of MCF-7 cells with 10 nM TCDD for 7 days reduced the cell growth to 60% of control; this effect was partly abolished by cotreatment of the cells with 100 nM 17 beta-estradiol (E2). The inhibition of cell growth by TCDD was accompanied by an enhanced secretion of transforming growth factor-beta (TGF-beta) and the TGF-beta content in cell culture supernatants was 2-fold higher than in controls. Using reverse transcription polymerase chain reaction (RT-PCR), the effect of TCDD on the expression of TGF-beta isoforms, transforming growth factor-alpha (TGF-alpha), tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) was investigated. It was demonstrated that incubation with 1, 10 and 100 nM TCDD for 24 h increased mRNA levels of TGF-alpha, TNF-alpha and IL-1 beta. The strongest effect was found on IL-1 beta, the mRNA level of which was dose-dependently increased. TCDD had a minor effect on TGF-alpha and TNF-alpha mRNA. The mRNA levels were significantly increased after treatment with 10 and 100 nM TCDD. The mRNA expression of TGF-beta 1 and TGF-beta 2 was unchanged, whereas the TGF-beta 3 mRNA level was enhanced 2 to 3-fold after TCDD treatment. From the results, we suggest that TCDD-induced growth inhibition in MCF-7 cells is related to the growth inhibitory action of a set of growth factors and cytokines which have a contextual action on MCF-7 cell proliferation.

Immunomodulation due to coexposure to styrene and dioctyl phthalate in mice

Pathomorphological and immunological alterations caused by a mixture of styrene and dioctyl phthalate were studied in albino mice following oral administration of 0.02, 0.03, 0.05 x LD50 of the mixture. The chemicals were mixed together proportionate to their respective LD50 values and fed in ground nut oil, 5 d/wk for 4 weeks. Histological examination of spleen revealed considerable depletion of cellular population of lymphoid follicles which corresponded to the dose dependent decrease in splenic mononuclear cell population count. The thymic lobules revealed slight atrophy but accompanied by a significant increase in thymocyte population. Correspondingly few significant histological changes were observed in mesenteric and peripheral lymph nodes. The treatment caused impairment of primary humoral immune response to SRBC (IgM) but there was a significant increase in response of splenocytes to B-cell mitogen LPS. There was a suppression of cutaneous delayed type hypersensitivity and increase in splenic lymphocyte response to T-cell mitogen PHA. Simultaneously, indirect immunity represented by decreased phagocytosis and enhanced metabolic function of reducing NBT by peritoneal exudate cells was observed. The in vitro exposure of vero cells to the mixture caused dose dependent protective effect. The results of present study indicate that subchronic exposure to low doses of mixture of styrene and dioctyl phthalate under certain conditions may modulate some of the immune functions as compared to exposure to either chemicals alone.

Production of complement component C3 in vivo following 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been shown to decrease serum complement C3 levels in female B6C3F1 mice but failed to alter C3 production when added in vitro to either hepatoma cells (both human and mouse hepatoma cells) or mouse primary hepatocytes (Lin and White, 1993a). It has also been demonstrated that mouse liver intracellular C3 levels were not affected following TCDD exposure in vivo, while serum C3 levels were suppressed (Lin and White, 1993b). Therefore, further studies were undertaken to investigate the mechanism by which TCDD modulates newly synthesized serum C3 in vivo. Mouse serum C3 was depleted by an intravenous injection of 50 anti-complement units (ACU)/kg cobra venom factor (CVF). This dose of CVF depleted serum C3 levels to 9% of control at 24 h after treatment. Subsequently, serum C3 levels returned to 19% and 75% of the control level on d 3 and d 5. The recovery of serum C3 was then monitored following an acute oral exposure to 20 micrograms/kg TCDD. In mice exposed to both TCDD and CVF, serum C3 levels reached 15% and 69% of control on d 3 and d 5 after treatment; these results were not significantly different from those of mice treated with CVF alone. Furthermore, when the radiolabeled amino acid [3H]leucine was injected intravenously into either vehicle- or TCDD-treated mice, the incorporation of this labeled precursor into both C3 and other secreted plasma proteins was not inhibited by TCDD. These results demonstrated that TCDD did not decrease newly synthesized C3 in vivo. These studies provide additional support for the concept that TCDD does not act directly on hepatocytes to suppress C3 production. The lower serum C3 levels observed in vivo following TCDD exposure is not the result of a decrease in C3 production by hepatocytes.

Inhibition of acute TCDD toxicity by treatment with anti-tumor necrosis factor antibody or dexamethasone

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) acute toxicity is characterized in part by a wasting syndrome with depletion of adipose tissue. Tumor necrosis factor (TNF) induces a similar response during chronic infection. The similarities of these toxic effects led to a hypothesis that TNF plays a role in TCDD acute toxicity. To test this hypothesis pharmacologic doses of an antibody specific for murine TNF and the potent anti-inflammatory agent Dexamethasone (DEX) were used to inhibit TCDD toxicity in mice. TNF antibody treatment resulted in a 54% reduction in TCDD-mediated mortality while DEX treatment, a glucocorticoid agonist that inhibits transcription of TNF, reduced mortality by 92%. Cyp 1A1 induction, the most commonly measured TCDD-mediated response, was not blocked by DEX, demonstrating separation of this biochemical effect from acute toxic responses to TCDD. These data suggest that TCDD-mediated changes in the TNF pathway may be an important mechanism for acute TCDD toxicity.

Increased endotoxin sensitivity following T-2 toxin treatment is associated with increased absorption of endotoxin

Oral exposure to T-2 Toxin (T-2) in experimental animals results in a syndrome similar to that observed in endotoxemia. Endotoxins are lipopolysaccharide, outer-membrane components of gram-negative bacteria which induce acute, inflammatory responses. In the present study, several aspects of endotoxin pathophysiology were investigated in mice following simultaneous exposure to T-2 and endotoxin, including mortality, hypothermia, tumor necrosis factor-alpha (TNF-alpha) and corticosterone production, and thymic weight. The disposition of endotoxin was also assessed, Acute, simultaneous exposure to T-2 (4 mg/kg, po) and endotoxin (3 micrograms/mouse, ip) resulted in increased mortality, hypothermia, TNF-alpha production, and thymic atrophy compared to treatment with either T-2 of endotoxin alone. Pretreatment of mice with endotoxin, a regime that renders the animals resistant to the effects of endotoxin, reduced many endotoxin effects in animals treated simultaneously with T-2 and endotoxin. Upon further investigation, it was observed that T-2 increased the absorption rate of endotoxin: as the peak height of serum endotoxin increased, the time-to-peak decreased, and the area under the curve was unchanged in animals treated simultaneously with T-2 and endotoxin. It was concluded that increased endotoxin absorption accounted for the increases in mortality, hypothermia, and TNF-alpha associated with T-2 exposure.

A review of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced changes in immunocompetence: 1991 update

2,3,7,8-tetrachlorodibenzo-p-dioxin, more popularly called dioxin or TCDD and referred to in this review as 2,3,7,8-TCDD, is considered the prototype of the polychlorinated dibenzo-p-dioxins (PCDD). The PCDD are true contaminants and are formed primarily as byproducts in the manufacture of materials requiring the use of chlorinated phenols and during the combustion of chlorinated chemical products. From an environmental perspective, the PCDD have been most closely associated with the use of a number of phenolic herbicides, including Agent Orange, which is a 1:1 mixture of the butyl esters of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). 2,3,7,8-TCDD and related PCDD are not produced commercially except in small amounts for research purposes and to date, have no known human benefit. 2,3,7,8-TCDD has been demonstrated to be the most potent and the most biologically active congener among the halogenated aromatic hydrocarbons (HAH), which include polychlorinated and polybrominated biphenyls (PCB and PBB, respectively) and the polychlorinated dibenzofurans (PCDF), in addition to the PCDD. An updated review on the effects of 2,3,7,8-TCDD on immunocompetence is timely from a number of perspectives. First, effects on immune function have been demonstrated to be among the earliest and most sensitive indicators of 2,3,7,8-TCDD-induced toxicity. Second, recent evidence indicates that exposure to 2,3,7,8-TCDD causes changes in innate immunity in addition to the changes in acquired immunity (i.e., which include effects on both cell-mediated and humoral immunity) previously shown to be associated with this chemical. Third, effects on immune function are almost universally observed among the animal species in which it has been evaluated, including some non-human primates. Fourth, effects of 2,3,7,8-TCDD on specific indicators of immune function have been correlated with changes in host resistance capabilities, which are often considered to be more holistic indicators of immunocompetence. Fifth, there are several reports which describe possible effects of 2,3,7,8-TCDD and related compounds (i.e., primarily PBB and PCB) on immune function in humans. It is important to emphasize at the onset that these studies have triggered much controversy, both political and scientific. However, it is equally important to speculate that at least part of the controversy associated with man's sensitivity to the immunological effects of 2,3,7,8-TCDD may be that the most appropriate approaches have heretofore not been applied. This possibility is discussed further in this review.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunosuppressive activities of polychlorinated biphenyls in C57BL/6N mice: structure-activity relationships as Ah receptor agonists and partial antagonists

The immunosuppressive activity of polychlorinated biphenyl (PCB) congeners is structure-dependent and 2 classes of compounds, namely the coplanar (class I) and monoortho coplanar (class II) congeners exhibit immunotoxicity. This study extends the structure-immunotoxicity relationships for PCBs by investigating representative congeners from the following structural classes of PCBs: monoortho coplanar (2,3,3',4,4',5-hexachlorobiphenyl, class II); monoortho coplanar minus a single parachloro group (2,3,3',4,5,5'-hexachlorobiphenyl and 2,3,3',4,5'-pentachlorobiphenyl, class III); diortho coplanar (2,3',4,4',5',6-hexachlorobiphenyl, class IV); triortho coplanar (2,2',4,4',5,6'-hexachlorobiphenyl, class V) and a tetraortho-substituted PCB (2,2',4,4',6,6'-hexachlorobiphenyl, class VI). The effects of these compounds on the splenic plaque forming cell response to sheep red blood cells was determined in 7-8 week old male C57BL/6N mice. The results showed that the class II-IV congeners were immunotoxic and with only one exception these compounds also induced hepatic microsomal aryl hydrocarbon hydroxylase and ethoxyresorufin O-deethylase activities and displaced [3H]-2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) from the cytosolic aryl hydrocarbon (Ah) receptor in competitive binding assays. These results thus extend the structure-activity relationships for PCBs as Ah receptor agonists. The interaction of these PCB congeners with an ED70-90 dose of TCDD (3.7 nmol/kg) showed that only one structural class of compounds, namely class III, partially antagonized TCDD-mediated immunotoxicity.

Studies on the role of lipid peroxidation in the acute toxicity of TCDD in rats

Lipid peroxidation has been shown to be enhanced following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but its role in TCDD toxicity is unclear. The present study was undertaken to further elucidate the relations between lipid peroxidation and TCDD lethality. A time course and dose-response experiment in Long-Evans (L-E; LD50 ca. 10 micrograms/kg) and Han/Wistar (H/W; LD50 greater than 3000 micrograms/kg) rats showed that hepatic lipid peroxidation, measured as the amount of thiobarbituric acid-reactive substances (TBA-RS), was induced by TCDD dose-dependently in L-E, but not in H/W rats. Hepatic glutathione peroxidase activity was suppressed in much the same manner in both strains. Lipid peroxidation correlated with body weight loss in L-E rats alone. When 500 micrograms/kg of TCDD was given to L-E rats, lipid peroxidation increased about 3-fold on Day 11 in the liver, while no change was seen in cardiac or renal TBA-RS. The pair-fed controls did not survive the 11-day test period and exhibited gastrointestinal hemorrhages. At 6 days, liver atrophy and elevated (over 2-fold) TBA-RS values were recorded in pair-fed controls but not in their TCDD-treated counterparts. TCDD decreased hepatic glutathione peroxidase activity by almost 50% at 6 days, while pair-feeding was without effect. Liver morphology was different between TCDD-treated and pair-fed rats. Moreover, the livers of TCDD-treated L-E rats contained much higher concentrations of probably peripheral fat-derived fatty acids than did the livers of pair-fed or ad libitum control rats. Restricted feeding over 6 days induced hepatic lipid peroxidation more in H/W than in L-E rats. Endotoxin increased liver TBA levels similarly in both strains having an additive effect with high doses of TCDD in H/W rats. Added as a 0.5% concentration in chow, butylated hydroxyanisole (BHA), but not ethoxyquin, tended to increase survival rate and time in L-E rats exposed to 20 micrograms/kg of TCDD; at 50 micrograms/kg the only survivor was again in the BHA group. However, neither antioxidant had any effect on initial body weight loss. It is concluded that lipid peroxidation mainly arises as a secondary phenomenon in TCDD toxicity, is not the cause of the typical histopathological liver lesion, but may contribute to lethality.

Immunotoxicology: suppressive and stimulatory effects of drugs and environmental chemicals on the immune system. A discussion

The fundamental characteristic of the adaptive immune system which has evolved in the vertebrates is the ability to recognise, and subsequently destroy, "foreign", and potentially harmful, antigens. The selective advantage which the immune system confers is the capacity to resist infectious, and possibly malignant, disease. It has been apparent for many years that individuals in whom immune function is impaired, due either to a congenital defect or to other factors such as treatment with certain immunosuppressive drugs, exhibit an increased susceptibility to infection and, in some cases, an elevated risk of developing at least some forms of malignancy. There is an increasing awareness from rodent studies that a variety of drugs and environmental chemicals have the potential to unintentionally impair components of the immune system. Risk assessment, based upon data from chemically induced changes in one or more parameters of immune function, is, however, dependent upon a knowledge of the functional reserve of the immune system. One of the objectives of the meeting from which this report derives was to examine what sources of information are available, and what experimental protocols can be employed, to permit accurate evaluation of immunological reserve. Although, under normal circumstances, the immune system selectively and specifically recognises foreign antigen, it is clear that the potential to recognise "self" is present and that in certain circumstances this potential is realised. Antibodies directed against normal tissue antigens have been shown to be associated with, and in some instances the presumptive cause of, "autoimmune" disease. There is a growing list of drugs and chemicals which are capable of eliciting autoantibodies and pathological autoimmune reactions. A second purpose of this meeting and of this report was to review the current state of knowledge regarding drug- and chemical-induced autoimmunity.

Characteristics of 2,3,7,8-tetrachlorodibenzo-p-dioxin induced endotoxin hypersensitivity: association with hepatotoxicity

Hepatic clearance is a major route of endotoxin detoxification. In the present study, the potential relationship between TCDD-induced endotoxin hypersensitivity and hepatotoxicity was examined. Acute doses of 50, 100, or 200 micrograms TCDD/kg body weight induced an endotoxin hypersensitive state in B6C3F1 mice as demonstrated by increased mortality 24-48 h following i.v. injection of endotoxin. This hypersensitive state occurred when endotoxin was administered 7 days following TCDD exposure, but not 1 day post-TCDD exposure. TCDD did not affect endogenous serum endotoxin levels. However, clearance of injected endotoxin was significantly inhibited following exposure to TCDD. Six hours post endotoxin treatment serum triglycerides were significantly increased in TCDD/endotoxin-treated mice compared to either treatment alone. Methylprednisolone and uridine were both examined in this model due to their roles in inflammation and RNA synthesis, respectively. Both compounds significantly reversed the mortality associated with the combined exposure. [3H]Uridine incorporation into liver was decreased following TCDD treatment alone, further suggesting impaired RNA synthesis. Studies performed on congenic mice indicate that the observed effects segregate with the Ah locus. The ability of methylprednisolone and uridine to reverse the mortality associated with TCDD/endotoxin treatment is consistent with an inflammatory response and impaired hepatic detoxification mechanisms. Thus, changes in hepatic handling of endotoxin, caused by progressive TCDD-induced liver dysfunction, may be responsible for the endotoxin hypersensitivity.

Styrene-induced immunomodulation in mice

Male mice given different oral doses (0.05, 0.03 or 0.02 x LD50/animal/day) of styrene (LD50 = 1 g/kg) daily for 5 days did not incite any overt toxicity in lymphoid organs or on hematologic parameters. At the tested dose levels styrene produced a mild reduction in the organ weight of adrenal and spleen and slight reduction in the cellular viability of lymph nodes. There was a dose-dependent suppression in the humoral immune response (IgM-producing PFCs of spleen and serum anti-SRBC HA titre) to SRBC. The proliferative response to the B-cell mitogen, LPS however revealed a significant increase in the incorporation of 3HT with middle and lowest doses of styrene. The results of cell-mediated immunity appeared somewhat unexpected and more complex as exposure resulted in a dose-dependent enhancement in the cutaneous DTH reaction to SRBC together with increased blastogenic response of splenic lymphocytes to phytohaemagglutinin (PHA). Additionally, there was significant impairment in the functional activity (NBT reduction, attachment and phagocytic indices) of nonadherent and adherent peritoneal exudate cells. Based on the present data the study identifies the immunotoxic potential of styrene and which acts differently on various arms of the rodent's immune system.

Elucidation of cellular targets responsible for tetrachlorodibenzo-p-dioxin (TCDD)-induced suppression of antibody responses: I. The role of the B lymphocyte

The objective of these studies was to identify the primary cellular target(s) responsible for TCDD (tetrachlorodibenzo-p-dioxin)-induced suppression of antibody production. Responses to T-independent and T-dependent antigens (administered in vivo or directly to splenic culture) were suppressed in a dose-related fashion in female B6C3F1 mice dosed for 5 consecutive days with 0.1, 1.0 and 10.0 micrograms/kg of 2,3,7,8-TCDD. When nonadherent (B and T) and adherent (macrophage) cells from vehicle- and TCDD-treated mice were combined in various combinations and immunized with either DNP-Ficoll (T-independent) or sRBCs (T-dependent), it was demonstrated that nonadherent cells, but not adherent cells, were functionally affected by TCDD. Similarly, as various combinations of B + macrophage and T + macrophage populations were immunized with sRBCs, the B cell was shown to be the primary target. Using LPS as the stimulus, an inhibition of the antibody response with no effect on the mitogenic response further indicated that the primary target of the TCDD-induced suppression of IgM antibody production is the B lymphocyte at the level of cell differentiation.

The immunopharmacology of immunotoxicology, and immunorestoration

The first part of this paper focuses on the secondary immunodeficiencies caused by immunosuppressive drugs and environmental chemicals. The mechanism of action and the therapeutic effects of azathioprine, glucocorticosteroids, cyclophosphamide, cyclosporin A, and anticancer drugs will be discussed. The immunotoxic actions of benzene, polychlorinated and polybrominated biphenyls, tetrachlorodibenzo-paradioxin, polycyclic aromatic hydrocarbons, various insecticides, metals and abused drugs or drugs with side effects are also described. Immunorestorative approaches are discussed in the second part, based on our current knowledge of the immune system and the lymphokines and hormones involved in its function. The usefulness of thymic hormones, interleukin 2, macrophage growth factor/colony stimulating factor, and interferons as immunotherapeutic agents is considered. In addition, we address chemically defined drugs, such as levamisole, diethyldithiocarbamate, isoprinosine, muramyl dipeptides, azimexon, ciamexon, bestatin, tuftsin, and pyrimidinoles, and finally conclude that combined use of different immunostimulants may be the most effective way to treat the above mentioned immunodeficiencies.

Interactions of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with immune responses of rainbow trout

Chlorinated dioxins, as typified by the most potent isomer, TCDD, are immunosuppressive in mammalian species and can enhance the susceptibility to a number of diseases. In recent years chlorinated dioxins have been detected in fish in many freshwater and marine habitats. Thus far, the effects of these chemicals on the immune responses of fish have not been examined. We studied the influence of TCDD on the defense mechanisms of rainbow trout. Yearling trout were injected intraperitoneally with the vehicle, 0.1, 1.0 or 10 micrograms/kg of TCDD. Interactions with the humoral immune response to sheep red blood cells (SRBC) were assessed by the Jerne plaque assay using head kidney and spleen leukocytes. Serum antibody was measured by complement-mediated lysis of SRBC in a chromium release assay. Effects of TCDD on the cellular immune responses were evaluated by the response of thymic and splenic lymphocytes to Con A and PWM. In addition, the phagocytic activity of peritoneal macrophages was examined in vitro. Trout which received 0.1 or 1.0 micrograms/kg TCDD remained clinically normal, and defense mechanisms were unaltered in these fish. Trout which received 10 micrograms/kg of TCDD became hypophagic and exhibited fin necrosis, ascites and suppression of hematopoiesis. In this treatment group, Con A-induced blastogenesis of thymic and splenic lymphocytes was not significantly changed, however, suppression of the PWM-induced response of splenic lymphocytes occurred. No statistically significant alterations occurred in humoral immune responses, and phagocytic activity of peritoneal macrophages was not decreased. The dose-response curve for various biologic effects of TCDD in the rainbow trout appears different from that in sensitive mouse strains. The 30-day, single-dose, parenteral LD50 for TCDD in the C57BL mouse is 100 micrograms/kg, and TCDD suppresses both cell-mediated and humoral immune responses at 1-2 micrograms/kg in this mouse strain. In the rainbow trout, however, immunosuppression was evident only at doses of TCDD approaching the 80-day, single-dose, parenteral LD50 of 20 micrograms/kg.

Evidence for lipid peroxidation in endotoxin-poisoned mice

Ethane has been identified and quantitated in air exhaled by mice following intraperitoneal injection of 20, 40, or 200 mg of Escherichia coli O111:B4 lipopolysaccharide (LPS) per kg. Significant increases in ethane concentration occurred within 1 to 5 h after LPS administration. In addition, increased concentrations of malondialdehyde were found in crude homogenates of livers obtained from mice 16 h after administration of 20 mg of LPS per kg. These results suggest that lipid peroxidation may be an important mechanism responsible for LPS toxicity.

Health implications of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) contamination of residential soil

Extrapolations from animal toxicity experiments (including carcinogenicity and reproductive effects) to possible human heath effects can be used to estimate a reasonable level of risk for 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD). Extrapolations are derived from: (1) review of published studies, (2) a complex set of assumptions related to human exposure to contaminated soil, and (3) estimates of (a) a dose response curve, (b) appropriate margins of safety, and/or (c) applicable mechanisms of action. One ppb of 2,3,7,8-TCDD in soil is a reasonable level at which to begin consideration of action to limit human exposure for contaminated soil.

Effects of 2,3,7,8-tetrachlorodibenzo-dioxin (TCDD) on early life stages of rainbow trout (Salmo gairdneri, Richardson)

Rainbow trout eggs, yolk sac fry and juveniles were exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in different concentrations for 96 h. Exposure of eggs to the lowest concentration, used in this study, 0.1 ppt (10-13 glg), resulted in a significant growth retardation for 72 days. At higher concentrations significant numbers of the forthcoming fry developed generalized edemas and died. Histologically, degeneration and necrosis of liver parenchymal cells were observed. Remaining fry showed teratologic changes as foreshortened maxillas and opercular defects. Administration of TCDD to yolk sac fry had similar effects. Juvenile rainbow trout, exposed to 10 and 100 ppt TCCD for 96 h, showed growth retardation and developed slight edematous changes. At 100 ppt all fry had died within 27 days. Histologically, vacuolization of the liver parenchymal cells and intracellular inclusion bodies in liver, pancreas and stomach were observed.

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the hepatic storage of retinol in rats with different dietary supplies of vitamin A (retinol)

The effect of various dietary sources of vitamin A on liver storage of retinol has been investigated in Sprague-Dawley rats treated with single oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): 0,0.1,1.0, or 10 microgram.kg-1. Each dose group consisted of 3 subgroups, each comprising 10 rats which received a diet with normal, low or high retinol content. The animals were killed 4 weeks after TCDD administration. Analyses of retinol were performed by high pressure liquid chromatography and glucuronosyltransferase activities were determined spectrophotometrically. A dose-dependent decrease in hepatic storage of retinol was evident. The high retinol diet did not fully compensate for the reduction caused by the highest TCDD-dose. Glucuronosyltransferase activity increased directly in relation to the TCDD-dose but in inverse proportion to the retinol content of the diet.

Examination of bone marrow, immunologic parameters and host susceptibility following pre- and postnatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The effects of pre/postnatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on various immunological, bone marrow and host susceptibility assays were examined in B6C3F1 hybrid mice. Exposure was accomplished by maternal dosing on Day 14 of gestation and again on Days 1, 7, and 14 following birth, employing dosages of 0, 1.0, 5.0 or 15.0 micrograms/kg body weight. The 15.0 micrograms/kg dosage was lethal to 70% of the offspring with the remainder of that dosage group revealing overt toxicity. Bone marrow toxicity occurred in both the 15.0 and 5.0 micrograms/kg dosage groups as evidenced by bone marrow hypocellularity and depressed colony formation of macrophage-granulocyte progenitor cells and pleuripotent stem cells. Evidence was presented that depression of lymphoproliferative responses following mitogen stimulation in TCDD-immunosuppressed mice was due to a functional defect of lymphocyte activation rather than suppressor cell activity. Administration of either Listeria monocytogenes or syngeneic PYB6 tumor cells in mice exposed to relatively low levels of TCDD during pre- and postnatal development increased their susceptibility to either bacterial or tumor challenge.

Effect of polychlorinated biphenyl, dibenzofuran and dibenzo-p-dioxin on the susceptibility of male mice to endotoxin

The effect of polychlorinated biphenyl (PCB), dibenzofuran (CDF) and dibenzo-p-dioxin (CDD) on endotoxin sensitivity was studied in male mice. The oral administration of CDF and CDD, once a week for 4 weeks, increased endotoxin sensitivity, whereas, PCB was not affective. On the other hand, residual levels of PCB were detected in thymus but CDF and CDD were not.

Role of the endocrine system in the action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the thymus

Several experiments were conducted to study the involvement of the adrenal and the pituitary gland in the acute toxic effects of TCDD. Adrenalectomized or hypophysectomized rats were treated with a single oral dose of 10 or 20 microgram of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg body weight. The reduced growth rate, the hepatotoxic effects and thymic involution induced by TCDD were not prevented by the adrenalectomy. The pituitary gland did not appear to be involved in causing thymic involution. In fact, the thymic effects of TCDD intoxication were even somewhat increased in hypophysectomized rats. Treatment with growth hormone failed to prevent thymic involution or the influence of TCDD on the liver.

Immunologic alterations by environmental chemicals: relevance of studying mechanisms versus effects

A number of environmental chemicals are known to modify the immune responses via a number of different mechanisms. Immunologic systems are vital to the well-being of individuals and a number of toxic effects are likely to be produced by chemical alteration of its processes. A variety of tests have been suggested for screening existing or new chemicals with regards to their potential to modify the immune responses. It is well recognized that immune responses are highly temporal (time-related) and the outcome of a test is likely to be influenced by the specific protocol employed and other factors that may involve the test organism. Although standardization of tests will probably reduce some of this variability, test standardization is not expected to provide more valuable information than can be already predicted by the routine evaluation of chronic toxicity and clinical parameters. The need for studying the mechanisms involved in the modification of immunologic processes by exogenous and even endogenous chemicals is emphasized in this report.

Laboratory studies on the immune effects of halogenated aromatics

The effects of TCDD exposure on the developing immune system were investigated in Wistar/Fischer hybrid or Fischer rats. Fetal and neonatal rats were exposed to TCDD through maternal dosing (5 muk/kg) on day 18 of gestation and on days 0, 7, and 14 of postnatal life (group 1). Another group of neonatal rats was exposed to TCDD through maternal dosing on days 0, 7, and 14 of postnatal life only (group 2). Variable but significant effects on body weights and thymus/body weight ratios were found up to 133 days of age. Cell mediated immune functions were depressed up to 133 days of age in both groups but less severely in animals exposed only postnatally. Furthermore, TCDD suppressed cell-mediated immune functions without affecting humoral immune function. Adoptive cell transfer studies indicated suppression of T-cell functions was selective in that "helper" cell function was not suppressed. In other studies, the effects on lymphocyte function following brief exposure of spleens from B6C3F1 mice to TCDD in dimethylsulfoxide (DMSO) were investigated. DNA, RNA and protein synthesis were inhibited at concentrations less than 2 X 10(-7) M TCDD in DMSO. This concentration accounted for approximately 0.2 ng TCDD uptake per spleen. The structurally related chemicals 3,4,3',4'-tetrachlorobiphenyl and 1-amino, 3,7,8-trichlorodibenzop-p-dioxin did not show significant lymphocyte effects even at two-fold higher concentrations. The ability of lymphocyte mitogens to bind to their cell surface receptors was not affected by TCDD treatment. TCDD was slightly cytolytic to lymphocytes after 48 hours of culture. DMSO treatment alone was also slightly toxic to lymphoid cells as indicated by a 10--20% loss of cell viability, although this occurred within 4 hours after DMSO exposure. Studies were performed to investigate the effects of 2,3,7,8-tetrachlorodibenzofuran (TCDF) on immune function in adult Hartley guinea pigs. Animals received 6 weekly doses of either 0, 0.05, 0.17, 0.5 or 1.0 microgram TCDF/kg body weight. TCDF slightly depressed cell-mediated immune functions, particularly at the higher dose levels as indicated by decreased lymphocyte blastogenesis, delayed hypersensitivity reactions, and production of macrophage inhibitor factor. Additionally, thymus-to-body-weight ratios were slightly reduced in the 0.5 and 1.0 microgram dosage groups. Serum IgG levels and antibody titer to BGG did not differ from controls. These results indicate that TCDF-induced immunosuppression is similar to that of TCDD.

Effects of 2,3,7,8-tetrachlorodibenzofuran (TCDF) on the immune system in guinea pigs

The effects of TCDF exposure on the immune system were investigated in Hartley guinea pigs. TCDF was administered by gavage at doses of 0.05, 0.17, 0.5 or 1.0 microgram/kg body weight once weekly for six weeks. Thymus/body weight ratios were suppressed in the higher dosage groups. Parameters of cell-mediated and humoral immune function were investigated. TCDF modestly suppressed cell-mediated immune function and had slight effects on humoral-mediated functions. TCDF immunosuppression appears similar to that induced following exposure to TCDD.

The effect of perinatal exposure to tetrachlorodibenzo-p-dioxin on the immune response of young mice

The immunocompetence of 5 week old offspring from mice fed control chow or chow containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was evaluated. The 5 ppb maternal feeding level was the only level that produced symptoms of intoxication in the offspring (i.e., facial alopecia and periorbital edema). Mice from mothers fed either 2.5 or 5 ppb of TCDD demonstrated thymus cortex atrophy and a significantly reduced spleen anti-SRBC plaque forming cell (PFC) response, but had normal serum anti-SRBC antibody levels following primary and secondary immunization. Contact sensitivity response to DNFB was significantly reduced only in offspring from mothers fed 5 ppb of TCDD. The blastogenic response of splenic T- and B-lymphocytes to concanavalin-A and E. coli lipopolysaccharide was unaffected by perinatal TCDD exposure. This correlated with the normal appearance of the T- and B-cell dependent areas of the spleens from these animals. There was no significant difference in the differential white blood cell counts between control and TCDD-exposed offspring. Offspring from mothers fed up to 5 ppb of TCDD withstood a live Listeria challenge as well as controls. However, maternal feeding levels as low as 1 ppb of TCDD rendered offspring more sensitive to an endotoxin challenge.