Impairment of thymus-dependent immune functions by exposure of the developing immune system to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Carcinogenic Effects of Infantile and Long-Term 2,3,7,8-Tetrachlorodibenzo-P-Dioxin Treatment in the Mouse

An infantile carcinogenesis assay was carried out with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) injections administered intraperitoneally at 0, 1, 30 and 60 μg/kg b.w. doses to (C57BL/6J × C3Hf)F1 (B6C3) and to (C57BL/6J × BALB/c)F1 (B6C) mice, starting from the 10th day of life, once weekly repeated 5 times. Animals were then observed until 78 weeks of age. The induction of thymic lymphomas was related to treatment at 60 μg/kg dose level in both sexes of both hybrids, and at 30 μg/kg dose level in both sexes of B6C mice and in male but not female B6C3 mice. The incidence of hepatocellular adenomas was increased by TCDD treatment at 60 μg/kg dose level in B6C3 of both sexes but not in B6C mice. Hepatocellular carcinomas were seen at increased incidence at 30 and 60 μg/kg doses in B6C3 males but not in B6C3 females or in B6C mice of both sexes. The incidence of other tumor types was not related to treatment in both hybrids. A long-term carcinogenesis bioassay with TCDD was carried out in B6C3 mice treated by gavage at 0, 2.5 and 5.0 μg/kg b.w. doses from 6 weeks of age, once weekly for 52 weeks. The animals were observed until 110 weeks of age. An increased incidence of hepatocellular adenomas and carcinomas was related to treatment, at both doses and in both sexes. The incidence of other tumor types was uniformly low in treated and control groups, without any association with treatment, in both sexes.

Developmental Activation of the AHR Increases Effector CD4+ T Cells and Exacerbates Symptoms in Autoimmune Disease-Prone Gnaq+/- Mice

Perinatal environmental exposures are potentially important contributors to the increase in autoimmune diseases. Yet, the mechanisms by which these exposures increase self-reactive immune responses later in life are poorly understood. Autoimmune diseases require CD4(+) T cells for initiation, progression, and/or clinical symptoms; thus, developmental exposures that cause durable changes in CD4(+) T cells may play a role. Early life activation of the aryl hydrocarbon receptor (AHR) causes persistent changes in the response of CD4(+) T cells to infection later in life but whether CD4(+) T cells are affected by developmental exposure in the context of an autoimmune disease is unknown. Gnaq(+/-) mice develop symptoms of autoimmune disease similar to those measured clinically, and therefore can be used to evaluate gene-environment interactions during development on disease progression. Herein, we examined the effect of AHR activation in utero and via lactation, or solely via lactation, on disease onset and severity in adult Gnaq(+/-) offspring. Developmental activation of the AHR-accelerated disease in Gnaq(+/-) mice, and this correlates with increases in effector CD4(+) T-cell populations. Increased symptom onset and cellular changes due to early life AHR activation were more evident in female Gnaq(+/-) mice compared with males. These observations suggest that developmental AHR activation by pollutants, and other exogenous ligands, may increase the likelihood that genetically predisposed individuals will develop clinical symptoms of autoimmune disease later in life.

Effects of developmental activation of the AhR on CD4+ T-cell responses to influenza virus infection in adult mice

BACKGROUND

Epidemiological and animal studies indicate that maternal exposure to pollutants that bind the aryl hydrocarbon receptor (AhR) correlates with poorer ability to combat respiratory infection and lower antibody levels in the offspring. These observations point to an impact on CD4+ T cells. Yet, the consequence of developmental exposure to AhR ligands on the activation and differentiation of CD4+ T cells has not been directly examined.

OBJECTIVES

Our goal was to determine whether maternal exposure to an AhR ligand directly alters CD4+ T cell differentiation and function later in life.

METHODS

C57BL/6 mice were exposed to a prototypical AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in utero and via suckling. We then measured CD4+ T-cell activation and differentiation into distinct effector populations in adult offspring that were infected with influenza A virus (IAV). Reciprocal adoptive transfers were used to define whether modifications in CD4+ T-cell responses resulted from direct effects of developmental TCDD exposure on CD4+ T cells.

RESULTS

Developmental exposure skewed CD4+ T-cell responses to IAV infection. We observed fewer virus-specific, activated CD4+ T cells and a reduced frequency of conventional CD4+ effector-cell subsets. However, there was an increase in regulatory CD4+ T cells. Direct effects of AhR activation on CD4+ T cells resulted in impaired differentiation into conventional effector subsets; this defect was transferred to mice that had not been developmentally exposed to TCDD.

CONCLUSIONS

Maternal exposure to TCDD resulted in durable changes in the responsive capacity and differentiation of CD4+ T cells in adult C57BL/6 mice.

Environmental toxicants and the developing immune system: a missing link in the global battle against infectious disease?

There is now compelling evidence that developmental exposure to chemicals from our environment contributes to disease later in life, with animal models supporting this concept in reproductive, metabolic, and neurodegenerative diseases. In contrast, data regarding how developmental exposures impact the susceptibility of the immune system to functional alterations later in life are surprisingly scant. Given that the immune system forms an integrated network that detects and destroys invading pathogens and cancer cells, it provides the body's first line of defense. Thus, the consequences of early life exposures that reduce immune function are profound. This review summarizes available data for pollutants such as cigarette smoke and dioxin-like compounds, which consistently support the idea that developmental exposures critically impact the immune system. These findings suggest that exposure to common chemicals from our daily environment represent overlooked contributors to the fact that infectious diseases remain among the top five causes of death worldwide.

Prenatal TCDD in mice increases adult autoimmunity

Two immunologically different mouse strains, C57BL/6 and SNF(1), were exposed to a mid-gestation dose of TCDD. The C57BL/6 mouse has a high-affinity aryl hydrocarbon receptor (AhR) and is sensitive to TCDD. The SNF(1) mouse has a low-affinity AhR but spontaneously develops autoimmune nephritis. Autoreactive Vβ(+)CD4(+)17a and Vβ(+)CD3(+) T cells were increased at 24-weeks-of-age in offspring of C57BL/6 mice, more so in females than males. The cytokine IFN-γ was elevated in the females, while IL-10 was elevated in males. Phenotypic changes in B-lineage cells were present in bone marrow and spleen, and circulating autoantibodies were increased after prenatal TCDD. Kidneys of males showed significant anti-IgG and anti-C3 deposition, suggesting early-stage autoimmune disease. The SNF(1) offspring similarly showed increased peripheral Vβ(+) cells in the females, increased autoantibody production in both sexes, and increased IFN-γ production in females. Male SNF(1) mice had increased anti-IgG and anti-C3 deposition in kidneys. Both mouse models therefore showed clear signatures of enhanced autoimmunity after prenatal TCDD.

Developmental exposure to the potent aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin Impairs the cell-mediated immune response to infection with influenza a virus, but enhances elements of innate immunity

Based on demonstrated effects on functional immunity in rodent models and supportive evidence from epidemiological studies, it is apparent that developmental exposure to ligands for the aryl hydrocarbon receptor (AhR) has the potential to impair immunity in human populations. Furthermore, due to the high levels of these compounds detected in human breast milk, and the fact that they cross the placenta, it is clear that humans are exposed to AhR ligands during fetal and neonatal development. The current studies were conducted to further characterize the relationship between developmental exposure to TCDD, the most potent AhR agonist, and defects in immune function later in life. Impregnated C57Bl/6 mice were treated with 4 doses of 1 mircog/kg TCDD, given on days 0, 7, and 14 of pregnancy, and 2 days after parturition. Functional immunity was assessed by challenging the adult offspring with influenza virus. Both male and female offspring of the TCDD-treated dams demonstrated impairment of the adaptive immune response, as evidenced by suppressed numbers of T cells and IFNgamma-producing cells in the draining lymph nodes and reduced T cell recruitment to the lung. In contrast, the inflammatory response, including infection-associated pulmonary neutrophilia and IFNgamma levels, was significantly elevated in the developmentally-exposed mice. These functional defects in immunity were not correlated with defects in hematopoeisis, as immune cells in the bone marrow, spleen, and thymus were phenotypically normal in uninfected mice. These results support the idea that immune alterations that arise during development cause persistent and significant changes in immune function.

Gestational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin disrupts B-cell lymphopoiesis and exacerbates autoimmune disease in 24-week-old SNF1 mice

Female SNF(1) hybrid mice spontaneously develop an immune complex-mediated glomerulonephritis as early as 24 weeks of age, whereas the disease onset in males is much slower. Further, a rise in concentration of glomerulus-specific autoantibodies via autoreactive B cells is critical to progression of the disease in this strain. Environmental factors contributing to the onset or degree of such autoimmunity are of interest yet poorly understood. In the present study, time-pregnant SWR x NZB dams (10/treatment) were gavaged on gestational 12 with 40 or 80 mg/kg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and the SNF(1) offspring were evaluated at 24 weeks of age. Bone marrow B220(low)CD24(-)AA4.1(+) committed B lineage progenitors were increased in female offspring by TCDD, however, committed progenitors and pro-B cells were decreased in males. Splenic marginal zone B cells (CD21(hi)CD24(low-int)) were decreased and follicular B cells (CD21(int)CD24(low)) were increased across sex by prenatal TCDD, whereas transitional-2 B cells (CD21(int)CD24(hi)) and (CD23(low-int) CD1(low-int)) were decreased in males only. Antibodies to double-stranded DNA were significantly increased across sex by TCDD. Anti-IgG and anti-C3 immune complex renal deposition was visibly worsened in females, and present in TCDD-treated males. These data suggest that developmental exposure to TCDD permanently and differentially alters humoral immune function by sex, and exacerbates a type III hypersensitivity lupus-like autoimmune disease in genetically predisposed mice.

An enhanced postnatal autoimmune profile in 24 week-old C57BL/6 mice developmentally exposed to TCDD

Developmental exposure of mice to the environmental contaminant and AhR agonist, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), causes persistent postnatal suppression of T cell-mediated immune responses. The extent to which prenatal TCDD may induce or exacerbate postnatal autoimmune disease remains unknown. In the present study, time-pregnant high affinity AhR C57BL/6 mice received a single oral administration of 0, 2.5, or 5 microg/kg TCDD on gestation day (gd) 12. Offspring of these mice (n=5/gender/treatment) were evaluated at 24 weeks-of-age and showed considerable immune dysregulation that was often gender-specific. Decreased thymic weight and percentages of CD4(+)CD8(+) thymocytes, and increased CD4(+)CD8(-) thymocytes, were present in the female but not male offspring. Males but not females showed decreased CD4(-)CD8(+) T cells, and increased Vbeta3(+) and Vbeta17a(+) T cells, in the spleen. Males but not females also showed increased percentages of bone marrow CD24(-)B220(+) B cell progenitors. Antibody titers to dsDNA, ssDNA and cardiolipin displayed increasing trends in both male and female mice, reaching significance for anti-dsDNA in both genders and for ssDNA in males at 5 microg/kg TCDD. Immunofluorescent staining of IgG and C3 deposition in kidney glomeruli increased in both genders of prenatal TCDD-exposed mice, suggestive of early stages of autoimmune glomerulonephritis. Collectively, these results show that exposure to TCDD during immune system development causes persistent humoral immune dysregulation as well as altered cell-mediated responses, and induces an adult profile of changes suggestive of increased risk for autoimmune disease.

Characterization of the antiallergic drugs 3-[2-(2-phenylethyl) benzoimidazole-4-yl]-3-hydroxypropanoic acid and ethyl 3-hydroxy-3-[2-(2-phenylethyl)benzoimidazol-4-yl]propanoate as full aryl hydrocarbon receptor agonists

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates most of the toxic effects of numerous chlorinated (e.g., TCDD) and nonchlorinated polycyclic aromatic compounds (e.g., benzo[ a]pyrene). Studies in AhR null mice suggested that this receptor may also play a role in the modulation of immune responses. Recently, two drugs, namely, M50354 and M50367 (ethyl ester derivative of M50354), were described as AhR ligands with high efficacy toward reducing atopic allergic symptoms in an AhR-dependent manner by skewing T helper cell differentiation toward a T H1 phenotype [Negishi et al. (2005) J. Immunol. 175 (11), 7348-7356]. Surprisingly, these drugs were shown to have minimal activity toward inducing classical dioxin responsive element-driven AhR-mediated CYP1A1 transcription. We synthesized and reevaluated the ability of these drugs to regulate AhR activity. In contrast to previously published data, both M50354 and M50367 were found to be potent inducers of several AhR target genes, namely, CYP1A1, CYP1B1, and UGT1A2. M50367 was a more effective agonist than M50354, perhaps accounting for its higher bioavailability in vivo. However, M50354 was capable of displacing an AhR-specific radioligand more effectively than M50367. This is consistent with M50354 being the active metabolite of M50367. In conclusion, two selective inhibitors of TH2 differentiation are full AhR agonists.

Effects of in ovo exposure to PCBs 126 and 77 on mortality, deformities and post-hatch immune function in chickens

In laboratory experiments, planar PCBs produce immune organ atrophy in chicken embryos. To study the immunotoxic effects of PCBs in birds, the coplanar congeners 3,3',4,4',5-pentachlorobiphenyl (PCB 126) and 3,3',4,4'-tetrachlorobiphenyl (PCB 77) were injected into the air cell of fertile white leghorn chicken eggs before incubation at doses of 0.25 and 0.5 ng/g egg PCB 126 and 0.64 ng/g egg PCB 77. Mortality and deformities were assessed during incubation of the eggs, and immune function was analyzed post-hatch using phytohemagglutinin (PHA) skin test for T-cell mediated immunity, antibody titers to sheep red blood cells (SRBC), mitogenesis of peripheral blood lymphocytes, and immune organ mass and cellularity. Exposure to 0.25 ng/g PCB 126 elevated mortality (61% and 69%) and deformities (31% and 32%), three or more times higher than controls. Two-fold suppression of antibody titers was observed in 28 day old chicks exposed to PCB 126 or PCB 77. No consistent alterations in PHA skin response or lymphocyte proliferation were observed. In 14 day old chicks in experiment two, PCB 126 decreased thymus and bursa cellularity by 33% and 35%, respectively. Immune organ atrophy was transient, recovering to control levels by 42 days of age. These experiments demonstrate that PCB 126 and 77 suppress antibody responses in juvenile chickens following an in ovo PCB exposure. Results reinforce the need for measuring multiple immune endpoints to detect immunotoxicity.

The comparative immunotoxicity of five selected compounds following developmental or adult exposure

It is well established that human diseases associated with abnormal immune function, including some common infectious diseases and asthma, are considerably more prevalent at younger ages. Although not established absolutely, it is generally believed that development constitutes a period of increased immune system susceptibility to xenobiotics, since adverse effects may occur at lower doses and/or immunomodulation may be more persistent, thus increasing the relative risk of xenobiotic exposure to the immunologically immature organism. To address this issue, a brief overview of immune maturation in humans is provided to demonstrate that functional immaturity alone predisposes the young to infection. Age-dependent differences in the immunotoxic effects of five diverse compounds, diethylstilbestrol (DES), diazepam (DZP), lead (Pb), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and tributyltin oxide (TBTO), which have undergone adult and developmental immunotoxicity testing in rodents, are then reviewed, as are human data when available. For all five chemicals, the developing immune system was found to be at greater risk than that of the adult, either because lower doses produced immunotoxicity, adverse effects were more persistent, or both.

Persistent suppression of contact hypersensitivity, and altered T-cell parameters in F344 rats exposed perinatally to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The outcome of perinatal low-level TCDD exposure on the T-cell-mediated contact hypersensitivity (CHS) response in adult F344 rats was investigated. Suppression of the 2,4-dinitrofluorobenzene (DNFB)-specific contact hypersensitivity reponse occurred in mature offspring of dams dosed by gavage with 1microg or 3microg TCDD/kg on gestation day (GD) 14. To determine if this effect was correlated with altered distribution or activation of major T-cell subtypes, cells of the auricular lymph node draining the hapten-treated skin were evaluated by flow cytometry for expressed phenotype, including activation markers, 24h after challenge. Six-month-old female offspring with significantly decreased CHS and born to dams given 3microg TCDD/kg, had significantly greater proportion of CD4(+) T cells expressing a naive phenotype marker, CD45RC(hi), in their draining nodes. The greater relative frequency of this CD4(+) subset in peripheral lymphoid tissues associated with a reduced CHS in these rats may be attributed to a reduction in the proportion of CD4(+) T cells maintaining or recruited into an activated state. The CHS proved to be a valuable bioassay for investigating long-term immunotoxic effects of perinatal TCDD exposure in rats.

The rat as a model in developmental immunotoxicology

Evidence is presented to demonstrate that the rat is a sensitive rodent species for developmental immunotoxicity testing of chemicals. A battery of immune function assays was performed in adult rats, which were exposed perinatally (i.e., during gestational, lactational, and/or juvenile development) to three different classes of environmental chemicals. The chemicals employed were the following: the organotins di-n-octyltindichloride (DOTC) and tributyltin oxide (TBTO); the polyhalogenated aromatic hydrocarbon 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD); and the organochlorine pesticides methoxychlor (MXC) and heptachlor (HEP). Suppression of immune function was observed in adult rats exposed to each of these chemicals during immune system development. The duration of immune function suppression in the rats so exposed ranged from three weeks (i.e., DOTC and MXC) to 19 months (i.e., TCDD) after the last exposure to the chemical.

Developmental immunotoxicology: emerging issues

While the history of immunotoxicology research involving experimental animals of immature ages dates back over several decades, there exist remarkably little data, to date, directly comparing the impact of developmental status on immunotoxicological risk. Given the size of the nonadult human population and the potential for differential vulnerability among the various ages, this represents a serious gap of knowledge in efforts to minimize environmentally linked health risks. This article frames the issues surrounding developmental immunotoxicological evaluations. In particular, the issues introduced include those of potential animal models, strain/genotype selection, gender, age of exposure, and age of assessment. Recent research results involving early exposure to lead (Pb) and other chemicals are discussed to highlight the nature of the decisions that are available and the potential cost-benefit associated with various approaches to evaluation.

Effects on fetal thymocyte populations and postnatal T-cell-dependent immune functions after maternal exposure to 5-fluorouracil during pregnancy in mice

5-Fluorouracil (5-FU) is a cytostatic anti-tumor drug which is known to have immunosuppressive activities. To assess the immunotoxic effects of 5-FU on fetal thymocyte populations and immune functions after birth, pregnant C57BL/6 mice were orally administered vehicle or 17 mg/kg/day of 5-FU during gestational days (GD) from 6 to 14. The fetal thymocyte populations were analyzed with flow cytometry (CD4/CD8 double staining), and immune functions (a mixed lymphocyte reaction, in vitro cytotoxic T-cell response, in vitro antibody-forming response) after birth were measured. Fetal thymus weight and thymocyte numbers were decreased by 5-FU administration. The decrease of the thymocytes was due mainly to the decrease of small CD4CD8 double positive (DP) thymocytes. The thymocyte numbers and populations recovered to the normal level 1 week after birth. The mixed lymphocyte response at the 6th week after birth tended to be slightly lower than the control levels, but the cytotoxic T-cell response and the antibody-forming response were the same as the control levels. These results suggest that immune functions might recover after birth, although maternal administration of 5-FU has a suppressive effect on fetal thymocyte maturation.

The retinoid signaling system--a target in dioxin toxicity

This review summarizes the available data on the effects of dioxins on retinoid levels, retinoid-related enzyme activities, and toxicological endpoints that have been correlated to retinoid effects. Similarities between dioxin toxicity and retinoid deficiency as well as retinoid excess are pointed out. Several possible levels of interaction between the dioxin and the retinoid signaling pathways are discussed, including the involvement of the Ah receptor, altered retinoic acid homeostasis, and an altered set point for retinoid storage. A hypothesis for the effect of dioxins on retinoids is suggested. In this hypothesis, comprising two cascades of effects on the molecular level, the effect of dioxins on retinoic acid levels is central.

Persistent suppression of delayed-type hypersensitivity in adult F344 rats after perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

Recently we observed a suppressed delayed-type hypersensitivity (DTH) response to bovine serum albumin (BSA) in the 4-5-month-old offspring of F344 rat dams receiving as little as 1.0 microg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg on gestational day (GD) 14. This study was designed to characterize better this suppression of the DTH response. First, the persistence of the DTH suppression was determined by measuring the DTH response to BSA in the offspring of dams dosed orally with 3.0 microg TCDD/kg on GD14 as well as in age-matched controls at 4, 8, 12 and 19 months of age. TCDD significantly suppressed the males' DTH response through 19 months of age. While the females' DTH response was reduced at 8, 12 and 19 months, significant suppression was observed only at 4 months of age. Secondly, the lowest maternal dose of TCDD that produced DTH suppression was determined by measuring the DTH response to BSA in the 4- and 14-month-old offspring of dams dosed orally with 0, 0.1, 0.3 or 1.0 microg TCDD/kg on GD14. In the males, suppression was observed at a maternal dose as low as 0.1 microg TCDD/kg at 14 months of age, while a maternal dose of 0.3 microg TCDD/kg was necessary to cause suppression in the 14-month-old females. Both males and females were more sensitive to the suppression at 14 months of age than at 4 months of age. Lastly, the DTH response to a second antigen was examined by measuring the DTH response to either BSA or keyhole limpet hemocyanin (KLH) in the 5- or 4-month-old male offspring, respectively, of dams dosed orally with either 0 or 3.0 microg TCDD/kg on GD14. The DTH response to both antigens was suppressed significantly. Phenotypic analysis was performed on thymus and lymph node suspensions. Significant effects in the thymus included an increased percentage of gammadelta TCR+ cells and a decreased percentage of gammadelta TCR+/CD4- CD8- and MHCI- MHCII- cells. In the popliteal lymph node draining the BSA-injected footpad, there was a decreased percentage of gammadelta TCR+ and MHCI- MHCII- cells and an increased percentage of MHCI+ cells. In conclusion, the suppression of the DTH response associated with perinatal TCDD exposure is persistent through late adulthood, occurs at a low dose (i.e. 0.1 microg TCDD/kg) to the dam, and is more pronounced in males than females. While phenotypic analysis identified differences in subsets of thymocytes and lymph node cells between control and TCDD exposed offspring, no clear correlations were established between altered subpopulations and suppressed DTH responses.

Effects of environmentally relevant concentrations of 2,3,7,8-TCDD on domestic chicken immune function and CYP450 activity: F1 generation and egg injection studies

Domestic chickens (Gallus gallus) were used as a surrogate species for wild turkey to assess risk from environmental 2,3,7,8-TCDD exposure. Lymphocyte proliferation and CYP450 induction were assessed in adults exposed via i.m. injection, in F1 14-day old hatchlings, in F1 adults (30-weeks old), and in 14-day old hatchlings exposed via yolk sac injections. Hatchlings from injected eggs exhibited a dose-response in lymphocyte proliferation, IgM titers, EROD, and PROD endpoints. Exposed adults showed a significant dose-dependent increase in CYP450 induction. F1 14-day old chicks exhibited a significant dose-dependent suppression of B-cell proliferation and induction of CYP450 enzymes. F1 adult proliferative responses exhibited B-cell suppression, that was not statistically significant. Significant sex-dependent EROD and MROD induction was also observed in F1 adults, indicating mixed-function oxidase imprinting from maternal exposure.

2,3,7,8-Tetrachlorodibenzo-p-dioxin co-stimulates staphylococcal enterotoxin beta (SEB) cytokine production and phenotypic cell cycling in Long-Evans rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmental contaminant that is considered to be a potent immunotoxicant. In the present study, we examined the effect of 25 micrograms/kg TCDD on cytokine production and T lymphocyte phenotype, cell cycling and receptor activity in female Long-Evans rats that had been injected with 50 micrograms of Staphylococcal Enterotoxin B (SEB). In the SEB-injected rats, TCDD increased the serum levels of interleukin-2 (IL-2) but did not affect the serum levels of interleukin-1 (IL-1), interleukin-6 (IL-6) or tumor necrosis factor (TNF). The ability of spleen cells and peritoneal cells to produce cytokines in response to SEB restimulation in vitro was also evaluated. TCDD exposure significantly enhanced IL-2 production by spleen cells from SEB-primed rats after 6 h or 24 h in cultures co-stimulated with SEB in vitro. However, TCDD treatment did not alter the production of IL-6 and TNF in these cultures. Although TCDD did not influence the production of IL-6 and TNF in peritoneal cells from SEB-primed rats with SEB restimultion in vitro, IL-1 production was significantly increased at 2 h. Both the kinetics and extent of SEB-induced IL-2 receptor (IL-2R) and T-cell receptor (TCR) expression on CD4+ cells was unaffected by TCDD. TCDD did not significantly alter the percentage or the total numbers of CD4+ and CD8+ subpopulations at various times after SEB injection. However, flow cytometric analysis showed that TCDD exposure increased the percentage of both CD4+ and CD8+ cells cycling in the S and G2M phase. TCDD, in the absence of SEB priming, did not affect any of the immune parameters tested. Nevertheless, collectively these results showed that TCDD can enhance the production of IL-2 and the percentage of CD4+ and CD8+ cells cycling in SEB-exposed Long-Evans rats. Histopatholgically, there were not observable effects of SEB on lymphoid organs while thymic atrophy and diffuse hepatocellular hypertrophy was observed in the TCDD-treated animals.

Age-related susceptibility to immunotoxicants: animal data and human parallels

There are numerous examples, of both the identical and different effects of animals exposure to toxic agents, which can be compared in both, exposed prenatal/neonatal animals and exposed adults. In some instances, although the chemical and its metabolites are stored for long periods in adipose tissue, adult exposure (short of acute poisoning) has little effect on the immune system (Johnson et al., 1986. An immunotoxicological evaluation of gamma-chlordane. Fundam. Appl. Toxicol. 6, 317-326), while exposure during gestation results in immunoteratology (Barnett, 1996. Developmental immunotoxicology. In: Smialowicz, R.J., Holsapple, M.P. (Eds.), Experimental Immunotoxicology, CRC Press, Boca Raton, FL, pp.47-62). With the heavily studied dioxins, both prenatal as well as adult exposure causes immunotoxicity, however, the effects are not always the same. Attempts to confirm these observations in humans have been hampered by a multitude of problems that are directly related to the exposure paradigm, such as lack of accurate exposure data, varying lengths of exposure, etc. as well as many variables that are simply related to differences in genetic makeup, lifestyle, socioeconomic status, etc. that are part of the human populations. A few studies have noted important trends in immune status that are correlated with levels of halogenated aromatic hydrocarbon exposures, however, even these fail to provide unequivocal answers regarding the relative risk of prenatal exposure.

Alterations in the developing immune system of the F344 rat after perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin I. [correction of II]. Effects on the fetus and the neonate

Perinatal exposure of rodents to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been shown to result in thymic atrophy and cell-mediated immune suppression at lower doses than are required to produce those effects following adult exposure. This study was designed to examine the effects that in utero TCDD exposure has on thymocyte development in the rat. Timed-bred pregnant F344 rats were given 0, 1.0, or 3.0 mcg TCDD/kg body weight by gavage on gestational day 14 (GD14). On GD19 or GD22/postnatal day one (PD1), the dams were euthanized, and the dams and their offspring were examined for organ weight and thymus phenotypic alterations. GD19 fetuses from the 3.0 mcg TCDD/kg maternal exposure group exhibited decreases in relative thymus weight and thymic cellularity. There were a decreased percentage of CD3-/CD4+ CD8+ thymocytes and an increased percentage of CD3-/CD4-CD8+ thymocytes in these fetuses, but there were no alterations in the CD3+ subsets. No effects were seen in the GD19 fetuses from the 1.0 mcg TCDD/kg dosage group. In the TCDD-exposed GD22/PD1 offspring thymic atrophy was no longer present, but there was an increase in the relative liver weight. In addition, there were decreased percentages of CD3-/CD4-CD8-, CD3+/CD4-CD8-, and CD3+/CD4+CD8+ thymocytes and an increased percentage of CD3+/CD4-CD8+ thymocytes. The CD3+/CD4-CD8- and CD3+/CD4-CD8+ cell populations were the most sensitive, with changes appearing at both 1.0 and 3.0 mcg TCDD/kg maternal exposures. The TCDD-exposed GD19 dams exhibited an increased relative liver weight, a decreased relative thymus weight, and alterations in thymic CD3+ populations. Three days later the relative organ weights had recovered in the dams, but the phenotypic alterations were seen in CD3- as well as CD3+ thymocyte subsets. These results indicate that the developing rat fetal thymus is susceptible to the effects of TCDD. In addition, pregnant rats and their offspring showed similar alterations in thymocytic phenotypes.

Alterations in the developing immune system of the F344 rat after perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin: II. Effects on the pup and the adult

Our recent work showed that in utero 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure produced alterations in fetal and neonatal thymocyte subpopulations. This study was designed to determine the persistence and functional significance of these alterations. One group of timed-bred pregnant F344 rats was dosed with 3.0 mcg TCDD/kg by gavage on gestational day 14 (GD14). The immune function of the perinatally-exposed offspring and age-matched controls were assessed at 14-17 weeks old. Examination of the organ weights and splenic phenotypes showed that TCDD exposure increased the spleen/body weight ratio, decreased the thymus/body weight ratio, and decreased the percentage of splenic CD3+/CD4-CD8- cells in both genders. The delayed-type hypersensitivity (DTH) response to bovine serum albumin (BSA) was suppressed in both the TCDD-exposed males and females. The lymphoproliferative (LP) responses to T-cell and B-cell mitogens and the antibody response to sheep red blood cells were not affected by perinatal TCDD exposure in either gender except for a suppressed LP response to PWM in the females. A second set of timed-pregnant F344 rats was dosed with 0 or 1.0 mcg TCDD/kg on GD14. One day after birth litters were cross-fostered to produce control, placental-only, lactational-only, and placental/lactational exposure groups. The organ weights and thymic and splenic phenotypes of these pups were assayed 1, 2, or 3 weeks post-partum, while the DTH response was assessed in 5-month-old males. Increased liver/body weight ratios, decreased percentages of thymic CD3+/CD4-CD8- cells, and increased percentages of thymic CD3+/CD4-CD8+ cells were seen through 3 weeks old in both genders after TCDD exposure. The severity of the effects was related to the route of exposure (i.e. placental/lactational > lactational > placental). The DTH response to BSA was suppressed in the males receiving both placental and lactational exposure. These results suggest that the immunotoxic effects of perinatal TCDD exposure of rats persist into adulthood and that suppression of the DTH response may represent the most sensitive biomarker for TCDD-induced immunotoxicity in this species.

Differential effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin, bis(tri-n-butyltin) oxide and cyclosporine on thymus histophysiology

Recent advances in the histophysiology of the normal thymus have revealed its complex architecture, showing distinct microenvironments at the light and electron microscopic level. The epithelium comprising the major component of the thymic stroma is not only involved in the positive selection of thymocytes, but also in their negative selection. Dendritic cells, however, are more efficient than epithelial cells in mediating negative selection. Thymocytes are dependent on the epithelium for normal development. Conversely, epithelial cells need the presence of thymocytes to maintain their integrity. The thymus rapidly responds to immunotoxic injury. Both the thymocytes and the nonlymphoid compartment of the organ can be targets of exposure. Disturbance of positive and negative thymocyte selection may have a major impact on the immunological function of the thymus. Suppression of peripheral T-cell-dependent immunity as a consequence of thymus toxicity is primarily seen after perinatal exposure when the thymus is most active. Autoimmunity may be another manifestation of chemically mediated thymus toxicity. Although the regenerative capacity of thymus structure is remarkable, it remains to be clarified whether this also applies to thymus function. In-depth mechanistic studies on chemical-induced dysfunction of the thymus have been conducted with the environmental contaminants 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and bis(tri-n-butyltin)oxide (TBTO) as well as the pharmaceutical immunosuppressant cyclosporine (CsA). Each of these compounds exerts a differential effect on the morphology of the thymus, depending on the cellular targets for toxicity. TCDD and TBTO exposure results in cortical lymphodepletion, albeit by different mechanisms. An important feature of TCDD-mediated thymus toxicity is the disruption of epithelial cells in the cortex. TBTO primarily induces cortical thymocyte cell death. In contrast CsA administration results in major alterations in the medulla, the cortex remaining largely intact. Medullary epithelial cells and dendritic cells are particularly sensitive to CsA. The differential effects of these three immunotoxicants suggest unique susceptibilities of the various cell types and regions that make up the thymus.

Breast-feeding exposure of infants to environmental contaminants--a public health risk assessment viewpoint: chlorinated dibenzodioxins and chlorinated dibenzofurans

Exposure of children to chlorinated dibenzodioxins and chlorinated dibenzofurans via breast-feeding has been well-documented in industrialized countries. Recent studies indicate a possible link between development of subtle health effects in children and their exposure to dioxin-like chemicals from maternal milk. Some examples of the effects are lower vitamin K levels, increased thyroxine levels, and mild changes in liver enzymes. The projected daily intakes of chlorinated dibenzodioxins and chlorinated dibenzofurans are compared with minimal risk levels for intermediate duration oral exposure (15-365 days) derived for these chemicals. Public health recommendations for future actions related to infant intake of chlorinated dibenzodioxin- and chlorinated dibenzofuran-contaminated breast milk are also addressed.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on humoral and cell-mediated immunity in Sprague-Dawley rats

There is much discussion about the occurrence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced effects on the human immune system. Extensive studies have been conducted in mice, but those results cannot explain some of the epidemiological data obtained in exposed humans. Therefore, studies in other laboratory animal species are needed. The aim of these experiments was to examine effects of TCDD on cell- and humoral-mediated immunity in male Sprague-Dawley (SD) rats. A delayed-type hypersensitivity (DTH) assay was used to examine cell-mediated immunity. A time-course study demonstrated that TCDD treatment on day -5 relative to immunization (day 0) produced the greatest effect on cell-mediated immunity. In a dose-response experiment, rats were treated with 1, 3, 10, 20, 30, 40 and 90 micrograms TCDD/kg The effect of TCDD on cell-mediated immunity displayed an inverted U-shaped dose-response curve, in that low doses enhanced and high doses suppressed this immune function. This is the first study to demonstrate an U-shaped dose-response curve of TCDD on the immune system. Primary antibody response to sheep red blood cells (SRBC) was used as endpoint to study the effect of TCDD on humoral immunity. Serum anti-SRBC IgM and IgG levels were measured using an enzyme-linked immunosorbent assay (ELISA). In the dose range examined (10, 20 and 40 micrograms TCDD/kg), serum IgM levels were not affected by TCDD compared to controls at 7 and 14 days after immunization. In contrast, serum IgG levels were dose-dependently elevated both 7 and 14 days after immunization, with a maximum increase of 59% over controls.

Immunotoxic effects of prolonged dietary exposure of male rats to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effects of low level exposure of rats to 2,3,7,8-tetrachlorodibenzo-p- dioxin (TCDD) on their immune system was investigated Dietary administration to young adult male Leeds strain rats of a total dose of 3 micrograms/kg body weight of TCDD resulted in an exposure duration-dependent reduction of in vitro lipopolysaccharide-induced production of interleukin (IL)-1 in cultures of their splenic macrophages. A 30-day exposure produced approximately 30% suppression and 180-day exposure produced approximately 52% suppression. This reduction did not negatively influence lipopolysaccharide- induced proliferation of B cells, instead an enhancement of B cell proliferation was observed after 30 days exposure. A 180 day exposure significantly suppressed the generation of IL-2 by either concanavalin A or phorbol myristate acetate/calcium ionophore stimulation, and reduced the lectin-induced proliferation of splenic T cells. The 30-day TCDD exposure showed no such immunotoxicity. TCDD at both exposure durations suppressed the expression of the alpha chain of the IL-2 receptor in concanavalin A-activated T cells, without affecting the CD4+/CD8+ ratio. The results suggest that exposure to a low dietary dose of TCDD suppresses the functions of several T cell subsets, some of the immunotoxic effects being produced early, while others require a longer exposure also down-regulates the IL-1 production function of macrophages. A common mechanism of TCDD immunotoxicity may be on the multifunctional signal transduction pathways downstream to the activation of protein kinase C and Ca2+ flux.

Minimal immunological changes in structurally malformed rats after prenatal exposure to cyclophosphamide

In order to compare the sensitivities of morphological and immunological parameters in a teratology study, effects in day 20 rat fetuses were studied after a single exposure to the immunosuppressive cytostatic agent cyclophosphamide (CP) on either day 11 or day 15 of gestation. Teratological methods included evaluation of external and skeletal morphology. Furthermore histology, immunohistochemistry and flow cytometry were performed on fetal thymus, liver and spleen. Immune function was assayed using the Trichinella spiralis infection model. Treatment resulted in dose-dependent gross morphological malformations, and in addition in overt skeletal anomalies such as brachygnathia, wavy ribs, and lordosis. In contrast, the immunological parameters tested revealed only minimal differences between treated and control groups. These results suggest either a remarkable recovery of the immune system after treatment, or a relatively high resistance of the immune system to the present treatment.

Evaluation of the effect of low-level 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure on cell mediated immunity

The immunotoxicity of TCDD in the mouse has been well documented. To date, the most sensitive endpoint to TCDD-induced toxicity in mice is that reported by Clark et al. (Clark, D. A., Gauldie, J., Szewczuk M. R. and Sweeney, G. (1981) Proc. Soc. Exper. Biol. Med. 168, 290.) who found that TCDD suppressed the murine cytotoxic T lymphocyte (CTL) response following four weekly doses of 4 ng TCDD/kg/week. However, these results have never been corroborated, as other laboratories have been unable to detect immunosuppression by TCDD at such low levels. In this study, we evaluated the effect of TCDD on the in vivo- and in vitro-generated CTL response to P815 mastocytoma cells in adult C57BL/6J female mice via a 51Cr release assay. Mice were given weekly intraperitoneal injections of TCDD or vehicle for 4 weeks at dosages ranging from 0.01 to 3.00 micrograms/kg/week. No statistically significant suppression of the in vivo- or in vitro-generated CTL response was detected at any dosage. As expected, significant increases in liver weights and decreases in thymus weights were observed at TCDD dosages of 1.0 and 3.0 micrograms/kg/week. Likewise, suppression of the antibody plaque-forming cell response to sheep erythrocytes was observed at dosages of 1.0 and 3.0 micrograms TCDD/kg/week. Although expected humoral immunosuppression and organ effects were observed, our data do not support suppression of murine CTL responses at the TCDD doses employed in this study.

Influence of prenatal maternal stress on the immunocompetence of the offspring

To evaluate the effects of prenatal maternal stress on the development of humoral immunocompetence in the offspring and on their hormonal and immunologic responses to postnatal stress, gravid Sprague-Dawley rats were exposed daily on gestational days 15-21 to prenatal environmental stress [(PES) 15 unsignaled, inescapable electric foot-shocks (0.05 mA for 0.5 s)] or prenatal psychological stress [(PPS) pregnant rats were placed in the nonelectrified section of the apparatus and allowed to see, hear, and smell a nonpregnant partner being environmentally stressed]. Pregnant controls (PC) were placed in the apparatus for 30 min. Serum corticosterone (CCS) and immunoglobulin G (IgG) levels were measured in the offspring every 7 days from birth to postnatal day (PND) 28. On PND 29-33, offspring were environmentally stressed; hormonal and immune status were determined on PND 34. Levels of IgG were reduced in PES and PPS offspring on PND 0 and in PES offspring on PND 7 and 28. These changes were unrelated to differences in CCS and did not reflect altered maternal-pup interactions or nutritional factors. Postnatal stress was immunosuppressive in PC pups but did not alter immune parameters in PPS offspring. In PES females, postnatal stress was also immunosuppressive. However, in PES males with already reduced IgG levels postnatal stress enhanced immune function. These data provide the first experimental evidence that prenatal maternal stress can alter immune parameters in the rat offspring.

Abnormal thymus development and impaired function of the immune system in rats after prenatal exposure to aciclovir

Aciclovir (synonym: acyclovir) causes abnormal thymus development in rats. After treatment on day 10 of gestation a weight reduction of the organ is obvious in 21-day-old fetuses which persists postnatally. Adult male rats exposed in utero to one or three injections of 100 mg aciclovir/kg body wt given to the dam on day 10 of pregnancy showed a reduction of the thymus weight to 333 +/- 158 mg and 276 +/- 61 mg (control: 428 +/- 92 mg; n = 10). Corresponding alterations were detectable in female offspring. Liver weight was also decreased and spleen weight (in relation to body wt) was significantly increased in the offspring after the three exposures. In a host resistance model with Trichinella spiralis the function of the immune system of rats prenatally exposed to aciclovir was examined. Six weeks postnatally 10-12 randomly selected male rat offspring of one control and two treatment groups (1 or 3 injections of 100 mg aciclovir/kg body wt on day 10 of gestation) were infected orally with 500 Trichinella spiralis muscle larvae. Before and several times after the infection blood was taken from a tail vein or obtained by decapitation for examination of the antibody titers (IgM, IgG, IgA, IgE) to antigens of T. spiralis. Six weeks after the infection the weight of relevant organs was determined and tongue preparations were used for T. spiralis muscle larvae counting. Aciclovir exposed animals showed a different immune response than control rats. IgM titers in both treatment groups were higher than in controls two weeks after the infection but not different by the end of the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in the cortical thymic epithelium of rats after in vivo exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): an (immuno)histological study

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces thymic atrophy in rats. The present study was initiated to provide (immuno)histological data on the mechanism of action. Juvenile male Wistar rats were orally intubated once with 50 or 150 micrograms/kg TCDD. They were euthanized 4 or 10 days thereafter, or were allowed to stay alive until Day 20 or 26. Growth retardation occurred rapidly in all TCDD-treated animals. Lethality was demonstrated within 20-21 days after administration. At Days 4 and 10 after intubation, thymic atrophy was shown by reduction of thymic weight and cortex/medulla ratio. Staining patterns for T-cell markers in the atrophic thymuses coincided with the reduction of cortical areas. There was no evidence indicating that the effects were indirectly caused by stress. TCDD-induced thymic atrophy persisted until Day 26 after administration. Immunohistochemical analysis revealed prominent changes in the cortical thymic epithelium at the 150-micrograms/kg dose level. First, in the cortex epithelial cell aggregates were observed both at Day 4 and at Day 10 after administration. Apparently, the architecture of the epithelium had changed in these animals. Second, at 10 days after administration epithelial cells were found with the simultaneous expression of markers that in the normal uninvoluted thymus only occur either in the subcapsular/medullary area or in the cortex. This phenotype points to an unusual stage of differentiation. We conclude that TCDD exposure affects the cortical epithelium of the rat thymus at a high dose level. Apparently, it disturbs the epithelial network and interfers with the differentiation of epithelial cells.

Exposure to tetrachlorodibenzo-p-dioxin (TCDD) alters fetal thymocyte maturation

We previously reported that thymic atrophy and reduced thymic cellularity associated with prenatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mice are characterized by quantitative alerations in the number of thymocytes expressing CD4 and CD8 surface antigens. In the present study, these observations have been extended to establish the specific thymocyte maturation processes affected by TCDD through an examination of cell size distributions, alpha beta and gamma delta T cell receptor (TCR) expression, peanut agglutinin (PNA) binding, and J11d marker analysis in murine thymocytes exposed prenatally to TCDD. Pregnant mice were administered vehicle, 1.5 or 3.0 micrograms/kg body wt TCDD by gavage on gestational Days (gd) 6-14. Flow cytometry analysis of gd 18 fetal thymocytes revealed a reduction in the number of small CD4+CD8+ double positive (DP) and PNA+, small thymocytes in the TCDD-exposed groups. The large cell population was reduced by TCDD to approximately 70% of control values. There was also a significant shift in TCR expression of thymocytes with a decrease in alpha beta TCR and a concommitant increase in gamma delta TCR expression from TCDD-exposed fetuses. The CD4-CD8+J11d+ thymocytes were increased in TCDD-treated mice while the more mature CD4-CD8+J11d- thymocyte numbers were similar to controls. Taken together, these data indicate that TCDD inhibits thymocyte maturation at the transition phase between the CD4-CD8+J11d+ phenotype and the DP/J11d+ thymocytes.

Perinatal thymocyte antigen expression and postnatal immune development altered by gestational exposure to tetrachlorodibenzo-p-dioxin (TCDD)

In utero exposure to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was found to alter expression of murine thymocyte fetal cell-surface markers. Pregnant mice were treated (via gavage) with 0, 1.5, or 3.0 micrograms TCDD/kg/day in corn oil on gestational days (gd) 6-14. Offspring were examined on gd 18 and postnatally on d6, d14, and d21, and at 7, 8, and 10 weeks of age. Severe thymic atrophy and cellular depletion were found both pre- and postnatally in TCDD-exposed mice. Immunocytochemical localization of the Thy 1.2 antigen on gd 18 thymocytes revealed no TCDD-related changes in cellular distribution. Flow cytometric analysis, however, indicated that the TCDD treatment resulted in a significant decrease in the percentage of CD4+8+ fetal thymocytes, as well as significantly increased CD4-8- and CD4-8+ thymocytes. The increased CD4-8+ population after TCDD was not from induction of Ts cells. At 7-8 weeks postnatally, no differences existed between control and treatment groups in mitogen responses and antibody plaque response. However, altered thymocyte antigen expression was found to correlate with altered postnatal immune function, as evidenced by decreased cytotoxic T lymphocyte response at 8 weeks of age. Taken together, these results indicate that immunosuppression following prenatal exposure to TCDD can be readily detected by qualitative and quantitative changes in the cell surface phenotype of fetal thymocytes. Furthermore, the observed altered distribution suggests that TCDD inhibits normal thymocyte maturational processes.

Polyhalogenated dibenzo-p-dioxins and dibenzofurans and the immune system. 2. In vitro effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on lymphocytes of venous blood from man and a non-human primate (Callithrix jacchus)

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on poke weed mitogen-stimulated proliferation and differentiation of peripheral lymphocytes was studied in vitro with cells from a non-human primate (marmoset monkey, Callithrix jacchus) and from man. Monoclonal antibodies and flow cytometry (FACScan) were used for analysis. The extent of the overall mitogen-stimulated proliferation of isolated lymphocytes in vitro from marmoset blood was only slightly reduced in the presence of TCDD compared to the solvent control (0.01% DMSO). However, incubation with TCDD in the culture medium together with the mitogen led to a pronounced decrease in the percentage of the lymphocyte subset with the surface marker CD4, and a concomitant increase in the percentage of CD8+ cells. The lowest concentration found to be effective in vitro was 1 x 10(-13) M TCDD (25 fg TCDD/ml). When culturing lymphocytes from human blood of different donors under identical conditions in the presence of TCDD and the mitogen, corresponding effects were observed to those seen with marmoset cells. A closer analysis of the T lymphocyte subsets affected revealed the CD4+ CDw29+ (helper-inducer cells) to be the main target for the action of TCDD. A clear-cut change in the percentage of this subpopulation was induced at concentrations as low as 1 x 10(-13) M TCDD. The development of the IL-2-marker in culture was only slightly affected by TCDD, and concentrations of 1 x 10(-12) M were required to slightly reduce the number of CD2+CD25+ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induced suppression of the local immune response

TCDD suppressed the normal immune response in popliteal and inguinal lymph nodes, when administered i.p. (50 micrograms/kg) to C57BL/6 mice, 4 days before immunization with the T-dependent antigen ovalbumin (10 micrograms/pad) in the hind foot pads. A hampered increase in lymph node cell number and a reduced frequency of antigen-specific B-cells were observed, despite the fact that cell proliferation in vivo was normal. While the restimulation of lymph node cells in vitro with ConA or LPS was normal, suggesting that the APC function was largely unaffected, the OVA-induced proliferation was greatly reduced. The anti-OVA antibody (ab) concentration both in serum and in supernatants of cultured lymph node cells was lower than in controls. In contrast, the production of anti-BSA ab upon LPS stimulation was normal. This indicates that the ability of the B-cells to produce ab and to proliferate was not disturbed. The DTH assay clearly showed an impaired T-cell function in TCDD-treated animals. Since APC or B-cells have appeared normal in their functions tested in this study, we propose that TCDD disturbed T-cell functions, leading to an impaired activation of B-cells.

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)

Neurobehavioral and immunological effects of prenatal cocaine exposure in rat

Time-pregnant Sprague-Dawley rats were injected subcutaneously with 20 mg/kg of cocaine HCl or 0.9% saline daily from gestation days 15 through 21. Maternal plasma levels of approximately 720 ng/ml of cocaine did not alter maternal weight gain during treatment, duration of pregnancy, any of the litter variables or several indices of maternal behavior. Offsprings' body weight from birth to 30 days of age and physical maturation were not generally affected by prenatal cocaine exposure. While the development of surface righting, cliff avoidance, and the startle response was accelerated in cocaine-exposed offspring, acquisition of a preference for a social odor was unaltered. Prenatal cocaine also attenuated the locomotor response of the offspring to d-amphetamine and cocaine at PND 15; at PND 30 both of these catecholaminergic agonists increased activity in prenatal saline and prenatal cocaine offspring. However, the difference in plasma levels of cocaine at PND 30 suggests a possible down-regulation of adrenergic receptors following prenatal cocaine exposure. Decreased thymus/body weight ratios and splenomegaly were observed in prenatal cocaine animals at 55 days of age. Although complete neutralization of herpes simplex virus-type 1 was not observed, sera from prenatal cocaine offspring showed an increased rate of appearance of cytopathic effect, while sera from animals given cocaine postnatally showed a reduction in the rate at which viral infectivity was expressed in culture. These results indicate that prenatal cocaine exposure can alter neurobehavioral ontogeny and humoral immune responsitivity in the offspring.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) treatment in vivo on thymocyte functions in mice after activation in vitro

Thymocytes from 15-day old C57BL/6 mice, pretreated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) 4 days before sacrifice, showed an earlier response and a higher maximal cell proliferation than thymocytes from control mice upon stimulation by concanavalin A in vitro. This is partly in contrast to the conclusions from earlier published studies. IL-2 content--as measured by growth of CTLL cells--was equally high in TCDD and in control cultures at day 1. At day 2, TCDD cultures had decreased dramatically in IL-2 content, possibly due to a high rate of consumption. At this point in time, the controls still contained a high concentration of IL-2, although less than at day 1. In contrast to the increased sensitivity to mitogen stimulation, thymocytes from TCDD-treated mice induced B-cells less avidly with respect to antibody production, and could also inhibit the T-cell help of thymocytes from untreated animals, a phenomenon which could be reversed if TCDD-treated thymocytes were irradiated before culture.

Effect of TCDD on the density of Langerhans cells in murine skin

Tetrachlorodibenzo-p-dioxin (TCDD) is a prototype for a group of toxic polyhalogenated aromatic hydrocarbons. We have studied the effect of TCDD on skin, specifically the difference in cutaneous response of congenic haired (hr/+) and hairless (hr/hr) mice. Topical application of 0.6 microgram of TCDD induces epidermal hyperplasia/hyperkeratinization in the skin of hr/hr mice, but does not affect the epidermis of congenic hr/+ littermates. Suppression of various parameters of the immune response has been found to be another effect of TCDD exposure in experimental animals. In the present study, we investigated the effect of topical treatment with TCDD on the density of epidermal immune cells, the Langerhans cells (LC), in the skin of hr/hr and hr/+ mice. Results showed that TCDD-induced epidermal hyperplasia/hyperkeratinization in skin of hr/hr mice is accompanied by an increase in the density of LC. In the skin of hr/+ mice, in which TCDD exposure does not induce hyperplastic changes, LC densities are not affected. The increase in LC densities in TCDD-treated hr/hr mouse skin did not result in increased sensitivity of the skin to contact hypersensitization with dinitrofluorobenzene, as measured by changes in ear thickness. When hr/hr murine skin was grafted into skin of hr/+ mice and the entire dorsal skin (including the graft) treated with TCDD, LC were increased in the grafted skin, but not in the surrounding hr/+ skin. Conversly, when hr/+ murine skin was grafted into hr/hr mice and both treated with TCDD, there was no increase in the density of LC in the grafted hr/+ skin. Concomitant treatment of hairless mice with TCDD and with indomethacin did not affect the increase in the density of LC induced by TCDD treatment alone. These findings suggest that TCDD-induced epidermal changes in hr/hr murine skin involve production of factors which mediate the increase in epidermal LC.

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.