Assessment of environmental contaminant-induced lymphocyte dysfunction

On the long-term effects of methyl isocyanate on cell-mediated immunity in Bhopal gas-exposed long-term survivors and their offspring

Methyl isocyanate (MIC) is a toxic industrial chemical that is documented as a potent respiratory toxicant. We investigated cell-mediated immunity (CMI) in the MIC-exposed long-term survivors and their offspring born after the Bhopal gas-leak tragedy in 1984. Several earlier reports show inconsistency in the assessment of immunological effects of MIC on the human population. In these studies, important factors including lifestyle attributes were overlooked. We incorporated these factors also in our study of the basic cell-mediated immune function in the Bhopal MIC-affected population. Twenty-seven years after exposure, we assessed the circulating T-lymphocyte frequency using E-Rosette assay. A total of 46 MIC-exposed healthy long-term survivors and their offspring were studied vis-a-vis parallel gender–age group-matched unexposed controls from Bhopal and various other regions of India. The influence of several lifestyle variabilities (smoking, alcohol intake, and tobacco chewing) on T-lymphocyte frequency was also taken into consideration. Our observations suggest that Erythrocyte-Rosette-forming cell (E-RFC) distribution frequency is largely insignificant in the MIC-affected population as compared to controls ( p > 0.05). In the MIC-affected tobacco chewers, there was a trend of suppression in CMI (relative decrease = 10.3%) as compared to nonchewers. Overall, our results show negligible long-term effect of MIC on CMI measured in terms of E-RFC frequency. These observations are not in agreement with earlier findings that immunosuppressive effects of MIC exposure persist in the T-cells of the affected population. However, atypical lymphocytes were frequently observed as E-RFC in the exposed females when compared to all other subgroups. Hematopoietic disorders (atypical lymphocytosis) in the MIC-affected population along with previous reports on the cytogenetic and humoral immune system linking cancer risk and chronic obstructive pulmonary disease (COPD) are important.

The transferability from rat subacute 4-week oral toxicity study to translational research exemplified by two pharmaceutical immunosuppressants and two environmental pollutants with immunomodulating properties

Exposure to chemicals may have an influence on the immune system. Often, this is an unwanted effect but in some pharmaceuticals, it is the intended mechanism of action. Immune function tests and in depth histopathological investigations of immune organs were integrated in rodent toxicity studies performed according to an extended OECD test guideline 407 protocol. Exemplified by two immunosuppressive drugs, azathioprine and cyclosporine A, and two environmental chemicals, hexachlorobenzene and benzo[a]pyrene, results of subacute rat studies were compared to knowledge in other species particular in humans. Although immune function has a high concordance in mammalian species, regarding the transferability from rodents to humans various factors have to be taken into account. In rats, sensitivity seems to depend on factors such as strain, sex, stress levels as well as metabolism. The two immunosuppressive drugs showed a high similarity of effects in animals and humans as the immune system was the most sensitive target in both. Hexachlorobenzene gave an inconsistent pattern of effects when considering the immune system of different species. In some species pronounced inflammation was observed, whereas in primates liver toxicity seemed more obvious. Generally, the immune system was not the most sensitive target in hexachlorobenzene-treatment. Immune function tests in rats gave evidence of a reaction to systemic inflammation rather than a direct impact on immune cells. Data from humans are likewise equivocal. In the case of benzo[a]pyrene, the immune system was the most sensitive target in rats. In the in vitro plaque forming cell assay (Mishell-Dutton culture) a direct comparison of cells from different species including rat and human was possible and showed similar reactions. The doses in the rat study had, however, no realistic relation to human exposure, which occurs exclusively in mixtures and in a much lower range. In summary, a case by case approach is necessary when testing immunotoxicity. Improvements for the translation from animals to humans related to immune cells can be expected from in vitro tests which offer direct comparison with reactions of human immune cells. This may lead to a better understanding of results and variations seen in animal studies.

Comparison of the immunoregulatory function of different constituents in radix astragali and radix hedysari

Radix Astragali (RA), known as “Huangqi” in China, is one of the most popular herbal medicines known worldwide to reinforce “Qi”. RA is traditionally prepared from the dried roots of Astragalus membranaceus (MJHQ) and A. membranaceus var. mongholicus (MGHQ). Radix Hedysari is named “Hongqi” (HQ), which is similar to RA. We assessed and compared the chemical constituents and bioactivity of RA and HQ. Different constituents were extracted into five major parts and were analyzed using different methods. Comparison of the immunological effects of extracts was done by using two immunological models. Results showed that flavonoids and saponins present in RA and HQ were not only structurally significantly different but also different in their immunological effect. Amino acids extract (AE) in MGHQ shows immunological effect while AE in MJHQ and HQ did not. Polysaccharides comprised the major constituents in RA and HQ. All polysaccharides extract (PE) of the three herbs showed similar levels of immunological effect in both immunological assays.

Resveratrol induces apoptosis, influences IL-6 and exerts immunomodulatory effect on mouse lymphocytic leukemia both in vitro and in vivo

Resveratrol, a dietary polyphenol found in grapes, has been proposed to act as a chemopreventive or anti-tumor agent in numerous epidemiologic studies. In this study, we investigate the antitumor and immunomodulation effects of resveratrol on mouse lymphocytic leukemia cells L1210 both in vitro and in vivo. Our finding indicates that resveratrol inhibits proliferation, induces apoptosis, and influences cell cycle of L1210 cells in a dose- and time-dependent manner in vitro. Furthermore, resveratrol can exert a dose-related regulatory effect on both innate and specific immune function to L1210-bearing mice. A normalization of CD4/CD8 ratios is noted as well as an enhancement of lymphocyte proliferation, NK cell activity and anti-SRBC titers. Interleukin-6 cellular content and release are suppressed by resveratrol as well as mRNA expression. In conclusion, the data provide new findings with respect to resveratrol mechanism of action to mouse lymphocytic leukemia.

Organochlorine contaminant exposure and associations with hematological and humoral immune functional assays with dam age as a factor in free-ranging northern fur seal pups (Callorhinus ursinus)

Potential effects of organochlorine contaminant (OC) exposure on humoral immune function and health of free-ranging northern fur seals were investigated. Forty-two "neonates" were captured for blood sample collection and re-sampled as "pups" 29-51 days later. OCs were extracted from whole blood to identify polychlorinated biphenyl congeners and chlorinated pesticides by high performance liquid chromatography. Humoral immune function was assessed by antibody responses to vaccination and immunoglobulin concentrations. Additional health status indicators included leukocyte counts and haptoglobin concentrations. Mean OC concentrations were higher in neonates than at recapture. Neonates of young dams had higher mean OC concentrations than neonates of older dams. A higher proportion of old dam's pups developed a twofold or greater increase in antigen-specific antibodies compared to young dam's pups. Higher OC exposure and poor immune responses in first-born pups may indicate a higher risk of secondary morbidity and mortality than pups of multiparous dams.

The role of the immune system in hexachlorobenzene-induced toxicity

Hexachlorobenzene (HCB) is a persistent environmental pollutant. The toxicity of HCB has been extensively studied after an accidental human poisoning in Turkey and more recently it has been shown that HCB has immunotoxic properties in laboratory animals and probably also in man. Oral exposure of rats to HCB showed stimulatory effects on spleen and lymph node weights and histology, increased serum IgM levels, and an enhancement of several parameters of immune function. Moreover, more recent studies indicate that HCB-induced effects in the rat may be related to autoimmunity. In Wistar rats exposed to HCB, IgM antibodies against several autoantigens were elevated; in the Lewis rat, HCB differently modulated two experimental models of autoimmune disease. Oral exposure of rats to HCB induces skin and lung pathology in the rat. Recently several studies have been conducted to investigate whether these skin and lung lesions can be related to HCB-induced immunomodulation, and these studies will be discussed in this review. HCB-induced skin and lung lesions probably have a different etiology; pronounced strain differences and correlation of skin lesions with immune parameters suggest a specific involvement of the immune system in HCB-induced skin lesions. The induction of lung lesions by HCB was thymus independent. Thymus-dependent T cells were not likely to be required for the induction of skin lesions, although T cells enhanced the rate of induction and the progression of the skin lesions. No deposition of autoantibodies was observed in nonlesional or lesional skin of HCB-treated rats. Therefore, we concluded that it is unlikely that the mechanism by which most allergic or autoimmunogenic chemicals work, i.e., by binding to macromolecules of the body and subsequent T- and B-cell activation, is involved in the HCB-induced immunopathology in the rat. Such a thymus-independent immunopathology is remarkable, as HCB strongly modulates T-cell-mediated immune parameters. This points at a very complex mechanism and possible involvement of multiple factors in the immunopathology of HCB.

Carrier effects of dosing the H4IIE cells with 3,3',4,4'-tetrachlorobiphenyl (PCB77) in dimethyl sulfoxide or isooctane

A rat hepatoma cell line, H4IIE, serves as a bioassay tool to assess the potential toxicity of dioxin-like chemicals, including polychlorinated biphenyls (PCB) in environmental samples. PCB exposure to these cells induces cytochrome (CYP) P4501A1 activity in a dose-dependent fashion, thus allowing assessment of mixtures. The objective of this study was to determine the effect of different carriers, dimethyl sulfoxide (DMSO) and isooctane on the concentrations of PCBs in the H4IIE cells and induction of CYP1A1 activity as measured by ethoxyresorufin O-deethylase (EROD) activity. H4IIE cells were dosed with three micrograms of UL-14C-PCB77/plate dissolved in DMSO or isooctane, and were harvested at sequential time periods for 4 days. PCB77 concentration and EROD activity were measured in the cells. EROD activity was greater when using DMSO as compared to isooctane, while there was no difference in the distribution of PCB77-derived radioactivities within the cell culture system based upon the carrier solvent used to deliver PCB77.

Immunotoxicity of PCBs (Aroclors) in relation to Great Lakes

Polychlorinated biphenyls (PCBs) are among the most widespread environmental pollutants and a prominent contaminant of the Great Lakes basin. Due to their resistance to biodegradation and lipophilic properties, PCBs bioaccumulate in fish tissues and in fish-eating humans. PCBs are also known to cross the placenta and to be excreted into the mother's milk, thus predisposing the infant to potentially adverse health effects. For example, a higher incidence of bacterial infections was reported for breast-fed infants born to mothers who consumed large amounts of Great Lakes fish compared to the incidence in control infants whose mothers ingested low amounts of fish. While data regarding the PCB-induced immunotoxic effects in humans are scarce, data derived from the use of experimental animals, including nonhuman primates, indicate that the immune system is a potential target for the immunotoxic effects of PCBs. Such studies have used the commercially available PCB mixtures alone. However, PCBs have the potential of partially antagonizing the effects of other structurally related compounds including the highly toxic dioxins, which are also present in small amounts in the Great Lakes. Thus, to fully evaluate the magnitude of the immunotoxic risk PCBs pose to humans, consideration should be given to investigations in which the interactive effects of PCBs are combined with other contaminants present in the Great Lakes.

Influence of arecoline on immune system: III. Suppression of B cell-mediated immune response in mice after short-term exposure

Arecoline, a major alkaloid of arecanut was examined to explore its modulatory influence on B cell-mediated immune response in a murine model system. The in vivo and in vitro effects were evaluated at sub-toxic concentrations of arecoline. The number of primary antibody forming cells (AFC) and hemagglutinating and hemolysis antibody titers to Sheep Red Blood Cells (SRBC) were evaluated in male mice. Arecoline exposure for a week invoked dose-dependent effect on primary antibody forming cells to SRBC with a maximum reduction at the dosage of 20 mg/kg bw, a moderate reduction at 10 mg/kg bw and no effect at 5 mg/kg bw dose level. HA and HL antibody titers to SRBC were suppressed markedly at arecoline dosage of 20 mg/kg bw and moderately at a dose of 10 mg/kg bw, given daily for 1, 2 or 3 weeks. The inhibitory effect of arecoline was not dependent on the duration of treatment. Like the primary antibody response, the secondary HA and HL antibody titers were also decreased after arecoline exposure. The administration of arecoline dosages 10 and 20 mg/kg bw daily for 4 days following SRBC immunization also, exerted dose-dependent suppression of primary antibody response. Similarly, when treated after 12 h following immunization, significant reduction in response was observed with arecoline dosage of 20 mg/kg bw. While moderate suppression of antibody response was noticed at the dose level of 10 mg/kg bw, there was no alteration in response at a dosage of 5 mg/kg bw.(ABSTRACT TRUNCATED AT 250 WORDS)

Dieldrin activates rat neutrophils in vitro

Suppression of phagocytic cell function has been proposed as a possible mechanism for the enhanced sensitivity to certain infectious agents exhibited by animals exposed to the organochloride insecticide, dieldrin. In the present study, we examined the effects of dieldrin on superoxide production by glycogen-elicited peritoneal neutrophils (PMNs) from the rat. Dieldrin caused a concentration-dependent increase in superoxide production by PMNs incubated in vitro at 37 degrees C. Superoxide release was increased significantly with 10 microM dieldrin and reached a maximum of 17 nmol/10 min/2.0 X 10(6) PMNs at a dieldrin concentration of 35 microM. Preincubation of PMNs for 5 min at room temperature with a barely suprathreshold concentration of either phorbol 12-myristate 13-acetate (PMA) or N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) enhanced dieldrin-stimulated superoxide release by as much as ninefold or threefold, respectively. Maximum enhancement was obtained with 10 microM dieldrin for both PMA and FMLP. Time course studies with PMA-pretreated cells revealed that the rate of superoxide release was dependent on the concentration of dieldrin. Extracellular calcium played an important role in dieldrin-stimulated superoxide release, since PMNs treated with dieldrin in the absence of extracellular calcium did not release superoxide. Also, pretreatment with calcium ionophore A23187 greatly enhanced superoxide release from dieldrin-stimulated PMNs. These results show that dieldrin has a stimulatory effect on superoxide release from rat PMNs in vitro and that this stimulation is dependent on extracellular calcium.

Suppression of allograft immunity by 3,4,5,3',4',5'-hexachlorobiphenyl. I. Effects of exposure on tumor rejection and cytotoxic T cell activity in vivo

There are conflicting reports in the literature concerning the immunotoxic effects of polychlorinated biphenyls (PCB) on cell-mediated immune responses. In the studies reported here, we show that the in vivo generation of cytotoxic T lymphocytes (CTL) in response to allogeneic tumor challenge is sensitive to suppression by 3,4,5,3',4',5'-hexachlorobiphenyl[(345)2-HxCB], a poorly metabolized, toxic, Ah receptor-binding PCB isomer. C57B1/6 mice treated with a single oral dose of (345)2-HxCB two days prior to the i.p. injection of allogeneic P815 tumor cells exhibited a dose-dependent reduction in peak CTL activity in the spleen. When examined on a kinetic basis, the CTL response was reduced in magnitude on all days examined with no evidence for a shift in the kinetics of the response induced by (345)2-HxCB exposure. (345)2-HxCB exposure prior to antigen challenge (day -14, -7, or -1 relative to P815 injection on day 0) produced significant suppression of the CTL response. (345)2-HxCB exposure 6 weeks prior to antigen challenge was still significantly suppressive, although the reduced degree of suppression suggested that recovery was in progress. When (345)2-HxCB exposure occurred after antigen challenge, significant suppression was produced only when exposure occurred within the first three days of the response, suggesting that, as the CTL matured, their sensitivity to (345)2-HxCB diminished. Clearance of the allogeneic tumor cells from the peritoneal cavity was delayed in (345)2-HxCB-treated mice and was associated with an altered composition of the white blood cell infiltrate in the peritoneal cavity. Symptoms of overt toxicity as well as immunotoxicity were apparent at lower doses of (345)2-HxCB in male as compared to female mice. In addition, interactive effects of (345)2-HxCB exposure and P815 antigen challenge on body weight and thymic involution were observed in both male and female mice. Possible mechanisms for the altered CTL response in (345)2-HxCB-exposed mice are discussed.

Identification of immunotoxic effects of chemicals and assessment of their relevance to man

Immunotoxicity is defined as the adverse effects of foreign substances (xenobiotics) on the immune system. Two types of effects are possible: immunosuppression (which may result in an increased susceptibility to infection or to the development of tumours) and immunopotentiation (which may manifest as an allergy or as autoimmunity). There is, as yet, little evidence that well controlled occupational exposure to industrial chemicals has led to clinically significant immunosuppression. In contrast, a number of industrial chemicals have been shown to cause immunopotentiation in exposed populations, producing occupational asthma and contact dermatitis and possibly autoimmunity. In experimental models, immunosuppression (usually assessed by in vivo or in vitro immune function tests) has been induced by a wide range of chemicals but there are a few reports of the immunosuppression leading directly to an increased susceptibility to infection or to the development of tumours. Predictive experimental models are available for type IV allergic reactions, but the identification of chemicals that have a potential to cause other types of allergy or autoimmune reactions requires further research and the development and validation of new animal models. It is considered that routine subacute and chronic toxicity studies should include a full gross and histopathological assessment of the lymphoid organs to more accurately detect the potential of a chemical to cause immunotoxicity. Should such studies indicate that a substance has affected the immune system directly, an assessment of overall immune competence and function tests may be necessary using dose levels below those which cause frank toxicity. However, precise interpretation of immune function tests in terms of their relevance to human health requires an improved understanding of the extent of the functional reserve of the immune system. A strategy for assessing immunotoxicity in exposed human populations demonstrates a need for reliable clinical assessment, accurate medical record-keeping, an environmental and biological monitoring for levels of contaminating chemicals and the judicious use of well-validated immune function tests.

Effect of lidocaine on the function of immunocompetent cells. II. Chronic in vivo exposure and its effects on mouse lymphocyte activation and expression of immunity

In vivo exposure of mice to lidocaine (0.25 mg/10 g body weight 4 times a day for 7 days) resulted in impairment of immunocompetent cell function. Spleen lymphocytes removed from animals immediately and 3 days after lidocaine exposure showed changes in their surface charge properties, inhibition of blastogenesis in response to concanavalin A and lipopolysaccharide, and inhibition of antigen-stimulated activation as measured by the mixed lymphocyte reaction. Lymphocytes from animals sensitized to keyhole limpet hemocyanin showed a significantly lower capacity to produce macrophage migration inhibitory factor 8 days after termination of exposure to lidocaine. Animals exposed to the drug were unable to accumulate an adequate number of immunocompetent cells at the site of challenge with a foreign substance (i.e. dextran), and the ability of the animals to destroy tumor cells nonspecifically and specifically was also impaired. The results indicated that chronic exposure to lidocaine resulted in impairment of lymphocyte function, even in the subsequent absence of the drug, and in significant changes in the expression of the immune response.

Macrophage induction of T-suppressor cells in pesticide-exposed and protozoan-infected mice

The use of infectious pathogens has allowed the detection of the development of synergism between pathogens and ubiquitous environmental chemical contaminants. This synergism has been demonstrated to result in a state of immunosuppression which either did not occur in the independent and singular presence of the chemical or pathogen and/or was greater than additive when both were combined. The immunosuppression was distinct with regard to the organochloride used and, therefore, is not a ubiquitous characteristic of all organohalides. The production of a macrophage soluble factor which appeared to induce T-suppressor cells was demonstrated in hepatic Kupffer cells from mice administered 5 ppm of dieldrin for 10 weeks and then infected with Leishmania tropical promastigotes. The factor was not generated in mice administered dieldrin and infected with malaria nor in mice administered only dieldrin nor in mice only infected with Leishmania. Additional studies revealed a profound impairment in macrophage antigen processing with macrophages obtained from mice administered dieldrin. The use of pathogen models may allow the immunosuppressive potential of environmental chemical contaminants to be expressed in a more sensitive manner.

Environmental chemical-induced macrophage dysfunction

Immunomodulation by environmental chemical contaminants and the role immune parameters play in toxicity and risk assessment studies is of increasing concern. Although considerable evidence has indicated that various xenobiotics may be immunosuppressive, little attention has been directed toward ascertaining a specific cellular locus which could be responsible for the impaired immune responsiveness. Since previous studies had suggested a macrophage defect in xenobiotic-induced immunosuppression and since macrophages are integral components of an immune response, an in-depth evaluation of macrophage function was conducted in xenobiotic-exposed mice. Macrophages isolated from mice receiving PCB, HCB, and dieldrin had no alteration in their in vitro O2 consumption while at rest or during phagocytosis. In addition, no alteration in in vitro phagocytic activity, phagocytic capacity or microbicidal activity was demonstrated. However, a significant impairment in the in vivo phagocytic clearance of a labelled antigen and an altered tissue distribution of the antigen was observed and was, perhaps, related, in part, to a significant decrease in serum fibronectin, an opsonic alpha 2 surface-binding glycoprotein. Furthermore, animals exposed to HCB and dieldrin, but not to PCB, had a profound decrease in their resistance to a challenge tumor cell implant which was related to a select alteration in tumor cell killing. The adherent spleen cells from HCB-treated mice had a profound suppression in their tumoricidal activity which was in contrast to dieldrin-treated mice, where the target cell type appeared to be the nonadherent cells. However, although dieldrin-exposed adherent cells (macrophages ?) did nt appear to have an altered tumoricidal capacity, all four macrophage types isolated from dieldrin-treated mice had a significantly impaired ability to process a cellular antigen. Splenic and alveolar macrophages appeared to be the most sensitive cell types to dieldrin. The present studies suggest that macrophage dysfunction may be an integral part of xenobiotic-induced immunosuppression and that the effector but not affector component of macrophage function may be the site of alteration.