Humoral immunotoxicity of polychlorinated diphenyl ethers, phenoxyphenols, dioxins and furans present as contaminants of technical grade pentachlorophenol

Biomarker Responses, Gene Expression Alterations, and Histological Changes in Zebrafish (Danio rerio) After In Vivo Exposure to Polychlorinated Diphenyl Ethers

Polychlorinated diphenyl ethers (PCDEs) have been detected in various aquatic matrices, which pose potential threats to aquatic ecosystem security. In this work, both micro and macro analysis methods were used to assess the toxicity of PCDEs to zebrafish. Results indicated that after in vivo PCDE exposure, the oxidative stress and related gene of Danio rerio were significantly changed. The higher concentration or longer exposure time could cause more severe oxidative stress in zebrafish tissues. Compared with among the five tested compounds, more obvious changes in the level of oxidative biomarkers of lower chlorinated PCDEs’ (4-mono-CDE and 4,4′-di-CDE) exposure groups were observed. The integrated biomarker response analysis and gene expression results also indicate a similar trend. Histopathological observation suggested that 4,4′-di-CDE could render liver nuclei enlargement and necrosis, hepatocyte vacuolation, and the development inhibition of ovarian cells. Transmission electron microscope photos showed that 4,4′-di-CDE caused organelle damage in the liver and ovary, including the rupture of the endoplasmic reticulum, swelling of mitochondria, and condensation of chromatin in the liver and mitochondria disappeared significantly in the ovary. The degree of damage is enhanced with the increasing exposure doses. In addition, PCDEs also significantly altered vitellogenin content and related gene (vtg1) expression, suggesting that PCDEs may be estrogen endocrine disruptors. Overall, these results provided some valuable toxicological data of PCDEs on aquatic species.

Polychlorinated diphenyl ethers (PCDEs) in surface sediments, suspended particulate matter (SPM) and surface water of Chaohu Lake, China

Polychlorinated diphenyl ethers (PCDEs) are typical halogenated aromatic pollutants that have shown various toxicological effects on organisms. However, the contamination status of PCDEs in the fresh water lakes of China remains poorly researched. In this study, the levels of 15 congeners of PCDEs in the sediments, suspended particulate matter (SPM) and water of Chaohu Lake were determined. The results showed that the ranges of concentrations of total PCDEs (ΣPCDEs) in the sediment, SPM and water were 0.279 ng g^-1 dry weight (d.w.)-2.474 ng g^-1 d.w., 0.331 ng g^-1 d.w.-2.013 ng g^-1 d.w. and 0.351 ng L^-1-2.021 ng L^-1, respectively. The most abundant congeners found in sediments, SPM and water were 3,3',4,4'-tetra-CDE, deca-CDE and 2,4,6-tri-CDE, with average contributive ratios of 17.36%, 15.48% and 20.63%, respectively. The medium and higher chlorinated PCDEs (e.g., penta- and deca-CDEs) were the dominant congeners in sediments and SPM. The percentages of lower chlorinated PCDEs (e.g., tri-CDEs) in the water were higher than those in the sediments. The combined input of ΣPCDEs from the eight main tributaries to Chaohu Lake was estimated at 6.94 kg y^-1. Strong linear correlations between the concentrations of ΣPCDEs and organic carbon (OC) contents in three type samples from Chaohu Lake suggested OC could influence the distribution of PCDEs in Chaohu Lake substantially. In addition, the calculated average organic carbon normalized partition coefficients (logK_oc) of 15 PCDEs between water and SPM were in the range of 4.55-5.45 mL g^-1. This study confirmed that Chaohu Lake is contaminated by PCDEs.

The immunotoxic effects of dual exposure to PCP and TCDD

Pentachlorophenol (PCP) was a commonly used fungicide, herbicide, insecticide, and bactericide in industrial, agricultural, and domestic settings; however, it was also contaminated with polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). It has been reported that technical grade PCP had immunosuppressive effects and that the immune system was the major target of PCDD/PCDFs toxicity. Although the immune response after exposure to PCP or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been studied, the toxic effects of exposure to both PCP and TCDD have not yet been reported. The aim of this study was to evaluate the effects on immune cells from mice intraperitoneally immunized with OVA and subsequently treated with PCP or TCDD alone or in combination by gavage. The animals were terminated on day 7 and 14, and the spleen and plasma samples were collected for immunotoxicity evaluation. The numbers and populations of splenocytes, T cell-derived cytokines produced by splenocytes, splenocyte-generated cytotoxicity and OVA-specific antibodies in plasma were investigated. Our results indicate that the spleen/body weight ratio and splenocyte number was reduced by TCDD alone; in addition, this reduction was enhanced when TCDD was combined with PCP. Exposure to TCDD alone or in conjunction with PCP suppressed many ovalbumin (OVA)-stimulated cytokines, including IL-2, IFN-γ, IL-4, IL-5, and IL-10. Furthermore, the immunoglobulins IgG and IgM were suppressed in mice administered by PCP alone, but the suppressive effects were greater in mice treated with TCDD alone or in combination with PCP. Co-exposure to PCP and TCDD resulted in an antagonistic effect on TCDD-induced suppression of IFN-γ and IL-10. Our results demonstrate that PCP alone is immunotoxic, regardless of the presence of TCDD. PCP led to mild changes in cytokine secretion, and it compromised splenocyte-generated cytotoxicity and IgM and IgG antibody production on day 7. The finding that PCP antagonizes TCDD-induced IFN-γ suppression could be due to the competitive binding of PCP to AhR (aryl hydrocarbon receptor).

Fatty liver and hepatic function for residents with markedly high serum PCDD/Fs levels in Taiwan

This study was designed to examine the associations between serum polychtorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) levels and adverse hepatic-related health outcomes. Residents living in the vicinity of a closed pentachlorophenol (PCP) manufacturing factory (exposure area) and other areas nearby (control area) were identified from prior investigation of serum PCDD/Fs measurements. A total of 85 subjects were recruited for the study, 52 from exposure area and 33 from control, respectively. Average level of serum PCDD/Fs was 80.1 6 50.9 pg WHO-TEQ/g lipid for those residing in exposure area, and 25.5 6 18.2 in control area. Statistically higher odds ratio (ORs) for fatty liver and gamma-glutamyltransferase (GGT) activity was found in subjects with higher serum PCDD/Fs levels and high body mass index (BMI) as compared to those with lower PCDD/Fs levels and less BMI. Data suggest that dioxin exposure and high lipid content affect the prevalence of fatty liver in exposed subjects. Future study should be directed to prevent continuous exposure to environmental PCDD/Fs from the defunct PCP factory, and to characterize prospectively, with a larger study sample size, the potential long-term consequences on hepatic function associated with contaminant exposure.

Polychlorinated diphenyl ethers (PCDEs): environmental levels, toxicity and human exposure: a review of the published literature

This paper reviews the state of the science regarding polychlorinated diphenyl ethers (PCDEs), a group of halogenated aromatic compounds, which are structurally related to polychlorinated biphenyls (PCBs) and polychlorinated dibenzofurans (PCDFs). Special attention is paid to the environmental levels, toxicity, and human exposure. PCDEs have been detected in a number of environmental samples, and their widespread occurrence in the environment is mainly the result of their presence as impurities in chlorophenol preparations. In humans, PCDE congeners have been detected in adipose tissue. As for other persistent organic pollutants (POPs), dietary intake is very probably the main route of exposure to PCDEs for the general population. However, data concerning PCDE levels in foodstuffs are very limited. It is concluded that investigations on experimental toxicity, dietary intake, and potential human health effects of PCDEs are clearly necessary.

Aryl hydrocarbon receptor-deficient mice generate normal immune responses to model antigens and are resistant to TCDD-induced immune suppression

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates many of the toxic effects induced by exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a high-affinity AhR ligand and a potent immunotoxicant. AhR-deficient mice have been constructed, and there are reports that the animals display altered splenic architecture and cellularity with an apparent increased incidence of infection. These observations have led to speculation that the immune system of these animals might be compromised, however, their functional immune response has not been directly tested. In the studies presented here, we examined the immune response of two strains of 8- to 10-week-old AhR-deficient mice. Mice were challenged with model antigens, allogeneic P815 tumor cells, or sheep red blood cells, and their ability to generate cell-mediated and humoral immune responses was examined. In addition, to address the obligatory role of the AhR in TCDD-induced immune suppression, we examined the immune response of the AhR-null animals following exposure to an immunosuppressive dose of TCDD. Results from these studies showed that AhR-deficient mice were able to mount normal productive immune responses to both model antigens and that neither the cellular nor the humoral response was suppressed by exposure to TCDD. Interestingly, however, we found that the immune response of heterozygous AhR(+/-) mice was less sensitive to TCDD than homozygous AhR(+/+) mice. The results of these studies suggest that the absence of the AhR does not impact the function of the immune system, but confirm the findings of previous studies that have indicated the AhR plays an obligatory role in TCDD-induced immune suppression.

Associations of blood levels of PCB, HCHS, and HCB with numbers of lymphocyte subpopulations, in vitro lymphocyte response, plasma cytokine levels, and immunoglobulin autoantibodies

Pentachlorophenol (PCP), hexachlorocyclohexane-[alpha], -beta, and -[gamma] (HCH-[alpha], -beta, and -[gamma]), polychlorinated biphenyls (PCBs), and hexachlorobenzene (HCB) are widely distributed industrial chemicals. They are suspected to induce immunologic impairments in exposed individuals. We examined dose-response relationships of blood levels of these chemicals with cellular (numbers of lymphocyte subpopulations, in vitro lymphocyte response) or humoral (plasma cytokine levels, immunoglobulin autoantibodies) immunologic dysfunctions. We studied 146 patients who had been occupationally exposed primarily to PCBs for more than 6 months. Lymphocyte subpopulations, in vitro responses to mitogens and allogeneic stimulator cells, plasma neopterin, cytokines, soluble cytokine receptors, soluble adhesion molecules, anti-Ig autoantibodies, and liver transaminases were determined. Blood levels of the different compounds were strongly correlated with one another. There were only weak dose-response relationships between blood levels of PCBs with cellular immune parameters, and of HCHs and HCB with humoral immune parameters. An exception was the statistically significant negative association of HCB with interferon-[gamma] (IFN-[gamma]), indicating that HCB has a significant impact on Th1 lymphocytes. Patients with HCB blood levels above the mean of 1,109 ng/L more often had undetectable IFN-[gamma] blood levels than patients below the mean. Patients with increased PCB 138 (> 710 ng/L) had more frequently undetectable interleukin-4 blood levels than patients with PCB 138 below the mean, and patients with increased PCB 101 (> 31 ng/L) more often had low DR+ cell counts in the blood (< 190/microL) than patients with PCB 101 below the mean. To assess possible cumulative effects, we compared patients who had blood levels of all compounds below background with patients who had blood levels of all compounds above background. Patients with low or absent blood levels of the compounds studied had higher IFN-[gamma] plasma levels, providing some evidence for a cumulative effect of several weakly active compounds. In conclusion, exposure to PCBs, HCB, or HCHs is associated with weak immunologic abnormalities. These results contrast with those obtained in earlier studies of blood levels of PCP, which showed a strong dose-dependent relationship with immunologic impairments. Our data suggest that long-term exposure of patients to HCB suppresses IFN-[gamma] production.

Association of elevated blood levels of pentachlorophenol (PCP) with cellular and humoral immunodeficiencies

It has long been suspected that pentachlorophenol (PCP) exerts a damaging influence on the immune system. In this study, the possible relationship between blood levels of PCP and immune function was studied in 190 patients who had been exposed for more than 6 mo to PCP-containing pesticides. The patients suffered from frequent respiratory infections and general fatigue. Lymphocyte subpopulations, in-vitro responses to mitogens, allogeneic stimulator cells, plasma neopterin, cytokines, soluble cytokine receptors, soluble adhesion molecules, and immunoglobulin autoantibodies were determined. A dose-response relationship between blood levels of PCP and cellular and humoral immune parameters was established. Blood levels of PCP were associated negatively with (a) total lymphocyte counts (p = .0002), CD4/CD8 ratios (p = .0015), and absolute counts of CD3+ (p < .0001), CD4+ (p < .0001), CD16+ (p < .0001), CD25+ (p = .0003), DR+ (p < .0001), CD8+/56+ (p = .020), and CD19+ cells (p = .092); (b) plasma levels of interleukin-2 (IL-2) (p < .0001), soluble IL-2R (p < .0001), IL-6 (p < .0001), IL-10 (p = .0039), interferon-gamma (IFN-gamma) (p < .0001), tumor necrosis factor-alpha (TNF-alpha) (p < .0001), transforming-growth factor-beta2 (p = .023), soluble IL-1 receptor antagonist (sIL-1 RA) (p < .0001), soluble intercellular adhesion molecule-1 (p = .0003); and (c) immunoglobulin (Ig) M-anti-Fab type autoantibodies (p = .0353). PCP levels were associated positively with (a) number of impaired stimulation assays per patient (p = .041); (b) number of circulating CD11b+ monocytes (p = .0015); and (c) plasma levels of neopterin (p < .0001), IL-4 (p = .020), and sIL-6R (p = .020). Compared with patients who had PCP plasma levels that were less than or equal to 10 microg/l, patients with blood levels of PCP that exceeded 10 microg/l experienced the following more often: low numbers of total blood lymphocytes (p = .054), CD3+ (p = .0014), CD4+ (p = .0001), DR+ (p = .0003), CD16+ (p = .0033), and CD25+ cells (p = .0033). In addition, the same aforementioned patients experienced the following more frequently: undetectable plasma levels of IL-2 (p = .0057), IL-6 (p = .042), IL-8 (p = .038), IL-10 (p = .0001), TNF-alpha (p = .0062), and IFN-gamma (p = .016); and impaired in-vitro responses of lymphocytes (p = .071). The authors concluded that increased blood levels of PCP were associated significantly with cellular and humoral immunodeficiencies. Recurrent respiratory infections and general fatigue could originate from PCP-associated immunosuppression.

Combined effects of pentachlorophenol and salinity stress on chemiluminescence activity in two species of abalone

The effect of pentachlorophenol (PCP) combined with salinity stress on hemocyte microbicidal activity was examined in two species of abalone. Microbicidal phagocytic function was determined in red (Haliotis rufescens) and black (Haliotis cracherodii) abalone after in vivo exposure to 25, 35 and 45 per thousand seawater salinity plus 1.2 mg/l PCP using luminol-dependent chemiluminescence (CL). Red and black abalone exposures of 3.5 and 6.5 h, respectively, were based on species-specific metabolic endpoints (MEPs) derived from previous nuclear magnetic resonance spectroscopy (NMR) data. Endpoints examined include total CL (CL(total)), peak CL (CL(max)), and the time to reach peak CL (T(max)). Overall, black abalone CL was significantly greater than red abalone CL particularly at ambient and high salinities. High salinity alone had a dramatic effect on red abalone whereas black abalone demonstrated few salinity effects. While the addition of PCP stimulated CL(max) and CL(total) among red abalone at ambient and high salinities, PCP exposure inhibited CL(max) at each salinity and inhibited CL(total) at ambient salinity among black abalone. Black abalone generally did not demonstrate effects of PCP within the 3.5 h exposure period except at high salinity plus PCP, which caused a reduction of CL(total). T(max) was greatly increased after PCP exposure at each salinity among red abalone but did not effect T(max) at any salinity tested among black abalone. No lysozyme activity was detected among red or black abalone after exposure to any of four different target particles tested either in the presence or absence of PCP. Overall, PCP in combination with salinity stress causes a modulation in the production of reactive oxygen species and this modulation varies between abalone species. Agents that decrease CL activity in hemocytes may reduce the antimicrobial potential of these cells thereby increasing susceptibility to infectious disease.

Immunotoxicity of pesticides: a review

The intricate balance that is the hallmark of the immune system shows vulnerability to any chemical, including pesticides, that can cause structural and functional alterations to the system. The immunotoxic effects of xenobiotics include: histopathologic effects in immune tissues and organs; cellular pathology; altered maturation of immunocompetent cells; changes in B and T cell subpopulations; and functional alterations of immunocompetent cells. Pesticides, including fungicides, herbicides, and insecticides, are the only class of chemicals deliberately released into the environment because of their toxicity. Around the world, millions of people are exposed to pesticides at work and/or in their home. This article reviews evidence, from animal and human studies, on the effects of pesticides on the immune system.

The immunologic evaluation of the Yucheng children

The immunologic effects of in utero exposure to polychlorinated biphenyls (PCBs)/polychlorinated dibenzofurans (PCDFs) were evaluated in the Yucheng children in this study. The study subjects consisted of 105 Yucheng children and 101 control children. The Yucheng children were born, between July 1978 and June 1987, to women who had exposed to high dose of PCBs/PCDFs through consumption of contaminated rice bran oil in 1978-1979. These children had been reported to have higher frequencies of bronchitis than their controls in the first six months of life, and higher frequencies of respiratory tract and ear infection in a 6-year follow-up. The low resistance of the Yucheng children to infection suggested that their immune function was suppressed by the PCBs/PCDFs they had exposed to in utero. In the summer and fall of 1995, a thorough physical examination and blood draw were performed on the study children. The Yucheng children were reported by their parents to have higher frequencies of influenza attacks than the control children during the six months prior to the examination. The frequencies of other symptoms were similar between the two groups. The serum levels of various immunoglobulins were similar between the two groups. Fifty-one serum samples, 29 of Yucheng and 22 of control children, were available for cell-mediated immunologic analysis. The percentages of various T cell markers, CD3, CD4, and CD8, and B cell and NK cell markers were not different between the Yucheng and the control children. No dose-response relationship was found between 27 Yucheng children's serum PCB/PCDF levels and any of their immunologic markers. WE concluded that 16 years after the Yucheng incident, Yucheng children exposed to high dose of PCBs/PCDFs in utero did not show, with the serum immunologic marker analyses, suppressed immunity when compared to their controls. To explain the consistent higher frequencies of upper respiratory tract infection in the Yucheng children, immune functional tests such as delayed hypersensitive skin reaction, in vitro lymphocyte proliferation, and antibody synthesis following immunization may be necessary.

Effect of pentachlorophenol on immune function

The organochlorine compound, pentachlorophenol, was evaluated for effects on immune system function in male Fisher 344 rats. Pentachlorophenol was prepared in an olive oil vehicle and was administered by oral gavage twice weekly for 28 days at a dose of 2.0 mg/kg per treatment. Exposure to pentachlorophenol increased body weight gains (P=0.024) during the treatment period. Liver (P=0.034) and kidney (P=0.012) body weight ratios were also increased. Pentachlorophenol exposure enhanced T-lymphocyte blastogenesis induced by concanavalin A (Con A)(P=0.0001) and phytohemagglutinin (PHA)(P=0.048) evaluated using stimulation indices. Corresponding B-lymphocyte blastogenesis induced by lipopolysaccharide/dextran (LPS/dex)(P=0.0034) was also enhanced by pentachlorophenol exposure. Pentachlorophenol suppressed the antibody response against sheep red blood cells (SRBCs) by 39% when the response was expressed per viable spleen cell (P=0.006). This suppression was not evident when the response was expressed per spleen (P=0.22), suggesting that a compensatory mechanism or extramedullary splenic hemopoiesis was occurring minimizing the overall impact on humoral immunity. The enhanced B- and T-lymphocyte blastogenesis may also reflect compensatory or hemopoietic activity. Pentachlorophenol exposure had no effect on peritoneal macrophage phagocytosis (P=0.31) or lymphocyte cell surface antigen expression. The observed alterations in lymphocyte blastogenesis and humoral immunity subsequent to pentachlorophenol exposure do not appear to be associated with phagocytosis or lymphocyte cell surface antigen expression.

Impaired in-vitro lymphocyte responses in patients with elevated pentachlorophenol (PCP) blood levels

Immune parameters were examined in 188 patients who were exposed for more than 6 mo to pentachlorophenol-containing pesticides. Blood levels of pentachlorophenol, lymphocyte subpopulations, in-vitro responses to mitogenic and allogeneic stimulation, plasma neopterin levels, and plasma cytokine and cytokine receptor levels were determined. Impaired in-vitro lymphocyte stimulation responses were impaired in 65% of the patients. The likelihood of impaired lymphocyte stimulation increased significantly with levels of pentachlorophenol that exceeded 10 microliters/l (p < .05). Patients who had high blood levels of pentachlorophenol and abnormal lymphocyte stimulation also had increased proportions of blood monocytes in blood (p < .05), as well as increased IL-8 serum levels (p < .02). Eleven patients who had abnormal mitogen stimulation experienced decreased CD4/CD8 ratios of < 1.0; 5 of these patients had decreased CD4+ lymphocyte counts of < 500/microliters, and 3 patients had increased plasma neopterin of > 15 nmol/l. These results indicate that increased levels of pentachlorophenol in blood can lead to severe T lymphocyte dysfunction.

Evaluation of the use of uncertainty factors in deriving RfDs for some chlorinated compounds

Risk assessment of exposure to chemicals having a toxic endpoint routinely uses the reference dose (RfD) approach based on uncertainty factors of 10. The purpose of this investigation was to evaluate whether the magnitude of the U.S. Environmental Protection Agency (EPA) 10x uncertainty factors has scientific merit when compared with data from recent human and animal experimental studies. A compilation and comparison of ratios between LOAEL/NOAEL (lowest observed adverse effect level/no observed adverse effect level) and subchronic/chronic values was made for six chlorinated compounds, namely, carbon tetrachloride, methylene chloride, pentachlorophenol, monochlorobenzene, chlorpyrifos, and 1,1-dichloroethane. Data sets demonstrated that 91.3% of the LOAEL/NOAEL ratios were < or = 6 while 87% of the ratios for the same parameter were < or = 5. Furthermore, subchronic/chronic ratios were < or = 3.5. From our investigation we concluded that automatic safety factors of 10x are not scientifically supportable and are overly conservative for the chlorinated compounds studied here.

An enzyme-linked immunosorbent assay (ELISA) specific for antibodies to TNP-LPS detects alterations in serum immunoglobulins and isotype switching in C57BL/6 and DBA/2 mice exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds

An enzyme-linked immunosorbent assay (ELISA) was developed to detect IgM and IgG antibodies specific for trinitrophenyl-lipopolysaccharide (TNP-LPS). Treatment of C57BL/6 and DBA/2 mice with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other aryl hydrocarbon (Ah) receptor agonists followed by immunization with TNP-LPS resulted in a dose-dependent decrease in serum IgM which paralleled the decrease in the splenic PFC response. The ED50 values for the IgM and splenic PFCs in C57BL/6 mice for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3',4,4',5-pentachlorobiphenyl (pentaCB) and 3,3',4,4',5,5'-hexaCB were 2.8 and 1.6, 11 and 14, and 25 and 20 micrograms/kg, respectively; in the less Ah-responsive DBA/2 mice, the ED50 values were 8.5 and 10, 61 and 69, and 73 and 71 micrograms/kg, respectively. In addition, treatment of C57BL/6 mice with TCDD resulted in alterations of serum IgG relative to IgM and a delay of isotype switching was observed after immunization and boosting with TNP-LPS. This ELISA may prove to be a useful tool in monitoring immune function during long-term exposure of mice to TCDD and related compounds and exploring the mechanism of Ah receptor-mediated immunosuppression.

Immunosuppressive effects of highly chlorinated biphenyls and diphenyl ethers on T-cell dependent and independent antigens in mice

The dose-dependent effects of 2,2',3,3',4,4',5,5',6-nonachlorobiphenyl (nonaCB), 2,2',3,3',4,4',5,6,6'-nonaCB, 2,2',3,3',4,5,5',6,6'-nonaCB and decaCB on the suppression of the splenic plaque-forming cell (PFC) response to the T-cell-dependent antigen, sheep red blood cells (SRBCs) and the T-cell-independent antigen, trinitrophenyl-lipopolysaccharide (TNP-LPS), were determined in genetically inbred mice. In addition, the induction of hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity was also measured. The highly chlorinated biphenyls suppressed the splenic PFC response to SRBCs in C57BL/6 and DBA/2 mice and were relatively more active in the former strain. The C57BL/6 mice are more responsive to aryl hydrocarbon (Ah) receptor agonists than DBA/2 mice and these data support a possible role for the Ah receptor in mediating this response. However, previous studies with polychlorinated biphenyls (PCBs) indicate that congeners with 3 or 4 ortho-chloro substituents are inactive as Ah receptor agonists and this was consistent with the minimal induction of hepatic microsomal EROD activity by the highly chlorinated biphenyls in both strains of mice. Thus, the results suggest that the inhibition of the splenic PFC response to SRBCs observed in this study was primarily an Ah receptor-independent response. Some of the highly chlorinated diphyenyl ethers namely decachlorodiphenyl ether and 2,2',3,3',4,4',5,6,6'-nonachlorodiphenyl ether, inhibited the antigenic response to TNP-LPS in C57 BL/6 mice. The results indicate that the suppression of the TNP-LPS-mediated immune response may be a more reliable indicator of the Ah receptor-dependent immunotoxicity of halogenated hydrocarbons.

Human pentachlorophenol poisoning

Pentachlorophenol (PCP) was, and still is, one of the most frequently used fungicides and pesticides. Its toxicity is due to interference with oxidative phosphorylation. Acute and chronic poisoning may occur by dermal absorption, inhalation or ingestion. Chronic poisoning occurs mainly in sawmill workers or people living in log homes treated with PCP-containing wood protecting formulations. Quantitative determination of PCP in urine and serum is useful to detect occupational or subclinical exposure. The clinical features of acute and chronic PCP poisoning can be classified systematically into effects on the skin, metabolism (fever), the haematopoietic tissue, the respiratory system, the central and peripheral nervous system, the kidney and the gastrointestinal tract. Although PCP is not classified as a human carcinogen, some epidemiological observations suggest that exposure to chlorophenols in general and PCP solutions in particular may result in an increased risk for certain malignant disorders such as nasal carcinoma and soft tissue sarcoma. There is concern that contamination of PCP-solutions with products such as chlorodibenzo-p-dioxins is the real cause of this suspected carcinogenicity. No specific antidote exists for the treatment of (acute) PCP poisoning. The basis of the treatment of acute poisoning is intensive supportive care with prevention of dangerous rise in temperature. Use of PCP-based products as indoor wood preservatives poses an unacceptable risk to human health.

Fluoranthene induces programmed cell death and alters growth of immature B cell populations in bone marrow cultures

Many studies have demonstrated that polycyclic aromatic hydrocarbons adversely affect mature mammalian immune systems. However, little is known about the cellular mechanism(s) mediating this immunosuppression or the potential for these ubiquitous environmental chemicals to similarly compromise lymphocyte development (lymphopoiesis). Murine bone marrow cultures were exploited in the present studies to evaluate the potential for fluoranthene, a mutagenic, cocarcinogenic, polycyclic aromatic hydrocarbon, to modulate B cell lymphopoiesis. In this well characterized system, interactions between immature bone marrow-derived precursor B (preB) cells and bone marrow-derived stromal cells closely mimic preB-stromal cell interactions in vivo and resemble interactions between other bone marrow-derived hematopoietic cells and their supporting stroma. Data presented herein indicate that: (i) fluoranthene suppresses B lymphopoiesis within 2 days in bone marrow cultures; (ii) fluoranthene suppresses lymphopoiesis at least in part by direct interactions with preB cells; (iii) fluoranthene lymphotoxicity is mediated by rapid induction of DNA fragmentation characteristic of programmed cell death (apoptosis) and (iv) preB cell populations surviving the initial death signal or preB cell populations exposed to lower doses of fluoranthene (0.5-5 micrograms/ml) exhibit altered growth and survival characteristics. The data suggest several levels at which fluoranthene could compromise B lymphopoiesis.

Halogenated aryl hydrocarbon-induced suppression of the in vitro plaque-forming cell response to sheep red blood cells is not dependent on the Ah receptor

The immunosuppressive effects of the halogenated aromatic hydrocarbons (HAHs), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 1,2,3,7,9-PeCDF and 1,3,6,8-TCDF were investigated utilizing the Mishell-Dutton model for in vitro immunization. The selected polychlorinated dibenzofuran congeners and 2,3,7,8-TCDD caused a concentration-dependent suppression of the splenic plaque-forming cell response to sheep red blood cells using cell cultures derived from C57BL/6 (Ah responsive) mice. Previous studies showed that there was up to a 14,900-fold difference in the in vivo immunotoxicity of these compounds, however in the in vitro studies, their immunosuppressive potencies were comparable. In addition, these congeners also exhibited similar potencies using spleen cell cultures from DBA/2 (Ah-nonresponsive) mice. Previous research demonstrated that alpha-naphthoflavone was relatively inactive in the in vitro splenic assay system and that co-treatment of cells from C57BL/6 mice with alpha-naphthoflavone (10 microM) plus 2,3,7,8-TCDD (20 mM) resulted in a significant inhibition of the immunotoxicity of 2,3,7,8-TCDD. In these studies, comparable interactive effects were also observed in cells treated with alpha-naphthoflavone plus 1,3,6,8-TCDF, a weak in vivo Ah receptor agonist. Collectively, the results from this study suggest that there may be mechanism(s) of action for HAH-induced suppression of the in vitro murine humoral response to sheep red blood cells which are independent of the Ah receptor protein.

Human lymphocyte reactivity after in vitro exposure to technical and analytical grade pentachlorophenol

To investigate the potential effects of technical pentachlorophenol (PCP-T, contaminated with polychlorinated dioxins and furans) and of analytical grade pentachlorophenol (PCP-A) on the human immune system, in vitro assays with freshly prepared human peripheral blood lymphocytes were used as an alternative to experimental animals. Both cell-mediated and humoral immune functions were examined after direct lymphocyte exposure to PCP-T or PCP-A at concentrations ranging from 0-200 microM. In each case the viability of the treated cells remained within the control value range. T lymphocyte blastogenesis after 3 days incubation with PCP was measured using both optimal and suboptimal mitogen (PHA) concentration. Interleukin-2 activity of 24.5-h supernatants of lymphocytes in response to PHA, pretreated with PCP for 20-24 h, was examined in a bioassay using the mouse IL-2-dependent CTLL-6 cell line. The synthesis of immunoglobulins was determined after stimulation with T-dependent (PWM) and T-independent (KlebsM) polyclonal B cell activators. In the proliferation assay the effects of PCP-T became more evident after suboptimal mitogen stimulation. Whereas after optimal mitogen stimulation blastogenesis was affected only at the highest concentration of 200 microM PCP-T, cell reactivity after suboptimal PHA stimulation was altered by all PCP-T doses. In the lower concentration range PCP-T caused enhanced proliferative responses, but at the two highest PCP-T concentrations cell reactivity was significantly suppressed as compared to the medium controls. Significant differences between the effects of PCP-T and PCP-A could be demonstrated only after optimal mitogen stimulation at the highest PCP concentration (200 microM). In contrast, lymphokine production as well as Ig secretion showed severe dose-dependent suppression after exposure to both PCP-T and PCP-A. The humoral immune response appeared to be more suppressed when cultures were stimulated with T-dependent rather than T-independent mitogens. The two different PCP preparations caused immunosuppression of both lymphocyte functions to the same extent. To summarize, the results of our studies indicate that PCP itself is directly immunotoxic to human immunocompetent cells and the T helper cell subset appears to be especially sensitive to PCP exposure. Furthermore, the observation of a direct effect on humoral immunity is similar to previous results showing considerable alterations of antigen specific antibody production in experimental animals after in vivo exposure.

Flow cytometric analysis of lymphocyte subpopulations in the spleen and thymus of mice exposed to an acute immunosuppressive dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The objective of the present studies was to determine if acute exposure to an immunotoxic dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces alterations in the expression of lymphocyte surface markers as measured by multiparameter flow cytometry. The immunotoxicity of a single oral dose of TCDD was assessed by the anti-SRBC PFC response; an ED50 of 0.74 micrograms/kg was determined. Subpopulations in the spleen and thymus of C57B1/6 mice were analyzed 2 days following exposure to 2 micrograms/kg TCDD. In addition, splenic lymphocyte subsets were examined on Days 1-4 following SRBC challenge of mice treated with 0, 2, or 5 micrograms/kg TCDD. T and B cells were identified by single parameter analysis of Thy 1.2 and Ig expression. T cell subsets were defined by dual parameter analysis of CD4 and CD8 expression. In TCDD-treated mice, the percentage and the total number of double-positive CD4+ CD8+ thymocytes were significantly decreased while the percentage but not the total number of double-negative CD4- CD8- thymocytes was significantly increased. No changes in the percentage or total number of single positive (CD4+ CD8- or CD4- CD8+) thymocyte subsets were observed. In contrast to the thymus, lymphocyte subsets in the spleen were not significantly altered in percentage or total number 2 days following acute TCDD exposure. When splenic lymphocytes were analyzed daily following SRBC challenge, Ig+, Thy 1.2+, and CD4+ CD8- subpopulations remained relatively unchanged in both control and TCDD-treated animals. A small but significant decrease in the percentage of CD4- CD8+ T cells was observed on Day 3 in mice treated with 2 or 5 micrograms/kg TCDD when compared to that of vehicle-treated mice. The total number of CD4- CD8+ splenocytes was also significantly lower in the 5-micrograms/kg group on Day 3. However, this effect appeared to result from an elevation of the CD4- CD8+ subset in the controls rather than from a reduction in the TCDD-treated groups. Double-positive (CD4+ CD8+) lymphocytes were not detected in either control or TCDD-treated spleens. These results indicate that an acute dose of TCDD which reduced the splenic anti-SRBC response by 65-80% did not cause detectable changes in major splenic lymphocyte subpopulations. This is an important finding from the standpoint of utilizing lymphocyte subset analysis to screen for potential immunotoxic effects of TCDD. Specifically, the absence of subset changes does not preclude the presence of functional immunosuppression.

Influence of the Ah locus on the humoral immunotoxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin: evidence for Ah-receptor-dependent and Ah-receptor-independent mechanisms of immunosuppression

There are conflicting reports in the literature regarding the role of the Ah locus in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) immunotoxicity. The present studies have utilized two congenic strains of C57Bl/6 mice that differ only at this locus to assess its influence on TCDD-induced suppression of antibody responses. Mice were given a single oral dose of TCDD 2 days prior to challenge with sheep red blood cells (SRBC) or trinitrophenyl-lipopolysaccharide (TNP-LPS). The subsequent dose-dependent effects of TCDD on the amount of antibody produced by splenic plasma cells were measured using the hemolytic antibody isotope release assay. In addition, the relative importance of the Ah genotype of lymphoid versus nonlymphoid tissue was examined in adoptive transfer experiments. Aryl hydrocarbon hydroxylase (AHH) activity was significantly induced in Ahbb mice by a dose of 0.5 micrograms/kg TCDD and maximally induced by a dose of 2 micrograms/kg. Ahdd mice required 10-fold higher doses of TCDD to induce comparable levels of AHH. The degree of thymic involution and liver hypertrophy induced by TCDD was also influenced by the Ah genotype of the animals. Both Ahbb and Ahdd mice exhibited dose-dependent suppression of the anti-TNP response following TCDD exposure. The ID50 was 7.0 micrograms/kg in Ahbb mice and 30.8 micrograms/kg in Ahdd mice. Suppression of the antibody response to SRBC was also dependent on the Ah locus. The ID50 in Ahbb mice was 0.6 micrograms/kg TCDD. However, an apparent biphasic dose response for suppression of the anti-SRBC response in Ahdd mice suggested the involvement of an Ah-independent component of suppression as well. In adoptive transfer studies, lymphocytes were identified as an Ah-dependent component of the response. The Ah-independent component of the response was not identified, and could be either lymphoid or nonlymphoid in nature. The possibility that T helper cells represent the Ah-independent component is discussed.

Polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and related compounds: environmental and mechanistic considerations which support the development of toxic equivalency factors (TEFs)

Halogenated aromatic compounds, typified by the polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and diphenylethers (PCDEs), are industrial compounds or byproducts which have been widely identified in the environment and in chemical-waste dumpsites. Halogenated aromatics are invariably present in diverse analytes as highly complex mixtures of isomers and congeners and this complicates the hazard and risk assessment of these compounds. Several studies have confirmed the common receptor-mediated mechanism of action of toxic halogenated aromatics and this has resulted in the development of structure-activity relationships for this class of chemicals. The most toxic halogenated aromatic is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and based on in vivo and in vitro studies the relative toxicities of individual halogenated aromatics have been determined relative to TCDD (i.e., toxic equivalents). The derived toxic equivalents can be used for hazard and risk assessment of halogenated aromatic mixtures; moreover, for more complex mixtures containing congeners for which no standards are available (e.g., bromo/chloro mixtures), several in vitro or in vivo assays can be utilized for hazard or risk assessment.

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans: the risks to human health. A review

1 PCDDs and PCDFs are ubiquitous and persistent in the environment. They are to be found in body tissues of both humans and animals. 2 The most extensively studied PCDD is 2,3,7,8-TCDD. It has been shown to produce a wide range of effects and is considered to be a (non-genotoxic) carcinogen in animals. 3 Studies into the mechanisms of toxicity so far reveal that there is involvement of a specific receptor (Ah), however further work is required to elucidate the mechanisms of the various effects. 4 Reports on a number of human exposures to PCDDs and PCDFs are described. Results from human epidemiological studies are difficult to interpret: there have been problems in methodology; there has been inadequate information on intake, and exposures have often been to mixtures of PCDDs and/or PCDFs together with other related compounds. 5 Many regulatory authorities faced with the problem of providing an index of risk from exposure to mixtures of PCDDs and PCDFs have employed the concept of 'TCDD equivalents'. 6 Whether or not PCDDs and PCDFs pose a significant human health risk at current levels of exposure they remain of considerable interest to the toxicologist.

Sister chromatid exchange and chromosomal breakage in pentachlorophenol (PCP) exposed workers

A cytogenetic study was performed on 20 healthy workers exposed to pentachlorophenol (PCP) in concentrations ranging from 1.2 to 180 micrograms/m3 (Maximum Concentration at the workplace is 500 micrograms/m3) for 3 to 34 years. PCP was determined in the blood plasma of all probands, yielding concentrations between 23 and 775 micrograms/l (Biological Tolerance Value is 1000 micrograms/l). In vitro PCP up to 90 mg/l was added to phytohaemagglutinin stimulated lymphocytes of normal healthy donors without any effect on sister chromatid exchange (SCE) or chromosomal aberrations (CA), whereas a slowdown of cell proliferation could be detected in the presence of 60 mg PCP/l. In vivo we neither observed a relation between PCP concentrations and the number of SCE nor an increase of CA.