Enhancement of the immune response in vitro by arsenic

Toxic effects of chemical warfare agent mixtures on the mussel Mytilus trossulus in the Baltic Sea: A laboratory exposure study

Baltic blue mussels (Mytilus trossulus) were implemented to assess potential toxicity, health impairments and bioaccumulation of dumped chemical warfare agents on marine benthic organisms. Mussels were collected from a pristine cultivation side and exposed under laboratory conditions to different mixtures of chemical warfare agents (CWAs) related phenyl arsenic compounds, Clark I and Adamsite as well as chloroacetophenone. Using a multi-biomarker approach, mussels were assessed thereafter for effects at different organisational levels ranging from geno-to cytotoxic effects, differences in enzyme kinetics and immunological responses. In an integrated approach, chemical analysis of water and tissue of the test organisms was performed in parallel. The results show clearly that exposed mussels bioaccumulate the oxidized forms of chemical warfare agents Clark I, Adamsite (DAox and DMox) and, to a certain extent, also chloroacetophenone into their tissues. Adverse effects in the test organisms at subcellular and functional level, including cytotoxic, immunotoxic and oxidative stress effects were visible. These acute effects occurred even at the lowest test concentration.

Arsenic exposure and prevalence of the varicella zoster virus in the United States: NHANES (2003-2004 and 2009-2010)

BACKGROUND

Arsenic is an immunotoxicant. Clinical reports observe the reactivation of varicella zoster virus (VZV) in people who have recovered from arsenic poisoning and in patients with acute promyelocytic leukemia that have been treated with arsenic trioxide.

OBJECTIVE

We evaluated the association between arsenic and the seroprevalence of VZV IgG antibody in a representative sample of the U.S.

METHODS

We analyzed data from 3,348 participants of the National Health and Nutrition Examination Survey (NHANES) 2003-2004 and 2009-2010 pooled survey cycles. Participants were eligible if they were 6-49 years of age with information on both VZV IgG and urinary arsenic concentrations. We used two measures of total urinary arsenic (TUA): TUA1 was defined as the sum of arsenite, arsenate, monomethylarsonic acid, and dimethylarsinic acid, and TUA2 was defined as total urinary arsenic minus arsenobetaine and arsenocholine.

RESULTS

The overall weighted seronegative prevalence of VZV was 2.2% for the pooled NHANES sample. The geometric means of TUA1 and TUA2 were 6.57 μg/L and 5.64 μg/L, respectively. After adjusting for age, sex, race, income, creatinine, and survey cycle, odds ratios for a negative VZV IgG result in association with 1-unit increases in natural log-transformed (ln)-TUA1 and ln-TUA2 were 1.87 (95% CI: 1.03, 3.44) and 1.40 (95% CI: 1.0, 1.97), respectively.

CONCLUSIONS

In this cross-sectional analysis, urinary arsenic was inversely associated with VZV IgG seroprevalence in the U.S.

POPULATION

This finding is in accordance with clinical observations of zoster virus reactivation from high doses of arsenic. Additional studies are needed to confirm the association and evaluate causal mechanisms.

Effect of prenatal arsenic exposure on DNA methylation and leukocyte subpopulations in cord blood

Prenatal arsenic exposure is associated with increased risk of disease in adulthood. This has led to considerable interest in arsenic's ability to disrupt fetal programming. Many studies report that arsenic exposure alters DNA methylation in whole blood but these studies did not adjust for cell mixture. In this study, we examined the relationship between arsenic in maternal drinking water collected ≤ 16 weeks gestational age and DNA methylation in cord blood (n = 44) adjusting for leukocyte-tagged differentially methylated regions. DNA methylation was quantified using the Infinium HumanMethylation 450 BeadChip array. Recursively partitioned mixture modeling examined the relationship between arsenic and methylation at 473,844 CpG sites. Median arsenic concentration in water was 12 µg/L (range<1- 510 µg/L). Log 10 arsenic was associated with altered DNA methylation across the epigenome (P = 0.002); however, adjusting for leukocyte distributions attenuated this association (P = 0.013). We also observed that arsenic had a strong effect on the distribution of leukocytes in cord blood. In adjusted models, every log 10 increase in maternal drinking water arsenic exposure was estimated to increase CD8+ T cells by 7.4% (P = 0.0004) and decrease in CD4+ T cells by 9.2% (P = 0.0002). These results show that prenatal exposure to arsenic had an exposure-dependent effect on specific T cell subpopulations in cord blood and altered DNA methylation in cord blood. Future research is needed to determine if these small changes in DNA methylation alter gene expression or are associated with adverse health effects.

Arsenic immunotoxicity: a review

Exposure to arsenic (As) is a global public health problem because of its association with various cancers and numerous other pathological effects, and millions of people worldwide are exposed to As on a regular basis. Increasing lines of evidence indicate that As may adversely affect the immune system, but its specific effects on immune function are poorly understood. Therefore, we conducted a literature search of non-cancer immune-related effects associated with As exposure and summarized the known immunotoxicological effects of As in humans, animals and in vitro models. Overall, the data show that chronic exposure to As has the potential to impair vital immune responses which could lead to increased risk of infections and chronic diseases, including various cancers. Although animal and in vitro models provide some insight into potential mechanisms of the As-related immunotoxicity observed in human populations, further investigation, particularly in humans, is needed to better understand the relationship between As exposure and the development of disease.

Vaccine specific immune response to an inactivated oral cholera vaccine and EPI vaccines in a high and low arsenic area in Bangladeshi children

BACKGROUND

Immune responses to the inactivated oral whole cell cholera toxin B (CTB) subunit cholera vaccine, Dukoral(®), as well as three childhood vaccines in the national immunization system were compared in children living in high and low arsenic contaminated areas in Bangladesh. In addition, serum complement factors C3 and C4 levels were evaluated among children in the two areas. VACCINATIONS: Toddlers (2-5 years) were orally immunized with two doses of Dukoral 14 days apart. Study participants had also received diphtheria, tetanus and measles vaccines according to the Expanded Program on Immunization (EPI) in Bangladesh.

RESULTS

The mean level of arsenic in the urine specimens in the children of the high arsenic area (HAA, Shahrasti, Chandpur) was 291.8μg/L while the level was 6.60μg/L in the low arsenic area (LAA, Mirpur, Dhaka). Cholera specific vibriocidal antibody responses were significantly increased in the HAA (87%, P<0.001) and the LAA (75%, P<0.001) children after vaccination with Dukoral, but no differences were found between the two groups. Levels of CTB specific IgA and IgG antibodies were comparable between the two groups, whereas LPS specific IgA and IgG were higher in the LAA group, although response rates were comparable. Diphtheria and tetanus vaccine specific IgG responses were significantly higher in the HAA compared to the LAA group (P<0.001, P=0.048 respectively), whereas there were no differences in the measles specific IgG responses between the groups. Complement C3 and C4 levels in sera were higher in participants from the HAA than the LAA groups (P<0.001, P=0.049 respectively).

CONCLUSIONS

The study demonstrates that the oral cholera vaccine as well as the EPI vaccines studied are immunogenic in children in high and low arsenic areas in Bangladesh. The results are encouraging for the potential use of cholera vaccines as well as the EPI vaccines in arsenic endemic areas.

Age-related effects of sodium arsenite on splenocyte proliferation and Th1/Th2 cytokine production

Aging is associated with immune dysfunction and conditions such as inflamm-aging and immunosuppression. Arsenic, an environmental contaminant distributed worldwide, affects the immune system. This study tested the hypothesis that arsenic has distinct effects on T cell proliferation and the production of cytokines by activated T cells. Murine splenocytes from young (2 months) and aged (24-26 months) C57BL/6 mice were exposed to arsenite (As(3+)), the most toxic form of inorganic arsenic, and stimulated with concanavalin A (Con A) or anti-CD3 antibody. T cell proliferation decreased significantly in response to Con A and anti-CD3 at subtoxic doses of arsenite in splenocytes from both young and aged mice. Arsenite, added concurrently with Con A or anti-CD3, significantly inhibited the production of interleukin-2 (IL-2), interferon-γ (IFN-γ), and interleukin-4 (IL-4) by splenocytes from young mice and significantly reduced the production of IL-10 by splenocytes from aged mice. In contrast, the production of IL-2 and IL-4 by splenocytes from aged mice was only slightly affected by arsenite. The results show that arsenic exposure reduces the immune response in splenocytes. Moreover, this effect may be influenced by aging.

Sodium arsenite mediated immuno-disruption through alteration of transcription profile of cytokines in chicken splenocytes under in vitro system

Arsenic is a ubiquitously found metalloid that commonly contaminates drinking water and agricultural food. To understand the ecotoxicological effects of arsenic in environment, it is essential to ameliorate the deleterious effects on human and animal health, particularly on the immune response. We investigated the effects of inorganic arsenic (iAs) on the immune response of chicken splenocytes. Both 1 and 10 mM concentrations of sodium arsenite treatment significantly reduced (P<0.001) splenocyte proliferation and phagocytic activity compared to concanavalin A (ConA) stimulated cells at 24, 48 and 72 h of incubation. Nitrous oxide (NO) production was significantly higher (P<0.001) at 24 h and subsequently declined in the higher dose group, while there was a gradual decline from 24 to 72 h in the lower dose group. Comparison of two different concentration of arsenic treatment also revealed time dependent differences. Relative quantification of expression of IFNγ and IL2 revealed that both genes were significantly down regulated (P<0.001) at both concentrations at each time point. iNOS gene was rapidly down regulated in splenocytes at 24 h at the high doses of As treated splenocyte, a gradual decreasing trend at low doses. Down regulation of IL-2 gene expression in response to As was further evidenced by a significant reduction (P<0.001) in the release of IL-2 into the splenocyte culture medium. We suggest that arsenic, a potent immunotoxic agent, modulates non-specific immune responses and alters the expression of cytokines in a dose and time dependent manner.

Effect of arsenic on regulatory T cells

INTRODUCTION

Arsenic (As) affects the function and survival of lymphocytes, and some arsenic compounds exert a relevant antineoplastic effect. We have explored the effect of As on T regulatory cells.

RESULTS AND DISCUSSION

In vitro experiments with peripheral blood mononuclear cells from healthy subjects showed that low concentrations of As tended to increase the number of natural T regulatory (nTreg) lymphocytes, whereas concentrations >5.0 muM had an opposite effect. Furthermore, rats exposed to As showed redistribution of nTreg cells, and As administration to rats with experimental allergic encephalomyelitis increased the levels of nTreg cells in spleen and diminished the severity of this condition. On the other hand, in 47 apparently healthy subjects chronically exposed to As, we found significant inverse correlation between urinary As levels and the number and function of nTreg lymphocytes. Although most of these individuals showed enhanced levels of apoptotic lymphocytes in peripheral blood, with a diminution of mitochondrial membrane potential, no significant correlation between these parameters and urinary As was detected.

CONCLUSION

Our data indicate that As seems to have a relevant and complex effect on nTreg cells.

Helper T cell subpopulations from women are more susceptible to the toxic effect of sodium arsenite in vitro

Arsenic is known to produce inhibition as well as induction of proliferative responses in animal and human cells depending on the doses. Despite the amount of information on the immunotoxic effects of arsenic exposure in different animal models, little is known in humans. Arsenic susceptibility of lymphocyte subpopulations (T helper (Th), CD4+; T cytotoxic (Tc), CD8+) and whether arsenic effects are gender related are still to be determined. This work evaluated the in vitro toxicity of sodium arsenite on human T lymphocyte subpopulations from men and women. Peripheral blood mononuclear cells (PBMC) obtained from healthy young men and women were treated with sodium arsenite (0.01, 0.1, and 1 microM). We assessed cell viability, cell proliferation, and the proportion of Th and Tc cells after 48 or 72h of arsenic exposure in resting and phytohemagglutinin M (PHA)-activated PBMC. We observed that sodium arsenite at 1 microM was more toxic for Th than for Tc cells in PBMC from women. Besides, T lymphocytes from women were more affected by the cell proliferation inhibition induced by arsenic, suggesting that women could be more susceptible to the toxic and immunotoxic effects caused by arsenic exposure.

A study on behavioral, neurotoxicological, and immunotoxicological effects of subchronic arsenic treatment in rats

Male Wistar rats were treated for 4, 8, and 12 wk with 3.33, 6.66, 13.3, or 26.6 mg/kg of inorganic arsenic (NaAsO(2)) per os by gavage. Changes in behavioral and electrophysiological parameters (spontaneous open-field exploration; electrocorticogram mean frequency and power spectrum; latency and duration of somatosensory, visual, and auditory evoked potentials; conduction velocity; and relative and absolute refractory period of a peripheral nerve) were determined. Treated rats exhibited hypoactivity of horizontal ambulation in the open field and showed depressed rates of grooming. The electrophysiological data, recorded from anesthetized rats, did not show any significant dose- and time-dependent changes. Changes in humoral immune response, tested after 4 wk of treatment, were not marked. The weight of organs responsible for immune response (thymus, spleen, adrenals), was significantly reduced, as were delayed-type hypersensitivity (DTH) reaction and mean cell volume (MCV) of red blood cells a hematological parameter. Plaque-forming cell (PFC) assay proved to be insensitive in this short-time exposure. These results suggest that subchronic low-level exposure to arsenic can affect immune responses and/or spontaneous behavior of rats.

Redox-linked cell surface-oriented signaling for T-cell death

T-cell death, which occurs either for ontogenic T-cell selection or for activated T-cell elimination, is normally induced through binding of a specific ligand to cell-surface T-cell receptor for crosslinkage. Heavy metals and carbonyl compounds that bind to protein-reactive groups such as cysteine sulfhydryl groups and lysine epsilon-amino groups may also induce crosslinkage of cell-surface proteins, in part replacing or modifying the ligand-mediated action. This chemical event has been found to accompany clustering of membrane rafts, to which signal-transducing elements such as glycosylphosphatidylinositol-anchored proteins and Src family protein tyrosine kinases (PTKs) are attached, and to trigger the signal transduction for apoptotic T-cell death, inducing mitochondrial membrane potential reduction, caspase activation and DNA fragmentation. As signals potentially upstream of this signaling, activations of PTKs and mitogen-activated protein (MAP) family kinases and production of reactive oxygen species (ROS) were induced following the cell-surface event, and crucial roles of activation of c-Jun amino-terminal kinase and apoptosis signal-regulating kinase 1 by a redox-linked mechanism in the cell-death signaling were demonstrated. Intriguingly, ROS production as well as PTK/MAP family kinase activation occurred in a membrane raft integrity-dependent manner. The redox-linked and cell surface-oriented signal delivery pathway demonstrated here may play an important role in induction of immune disorders by protein reactive group-binding chemicals.

Mitogenic activity of (-)epigallocatechin gallate on B-cells and investigation of its structure-function relationship

(-)Epigallocatechin gallate (EGCg), the main constituent of green tea, strongly enhanced the direct plaque-forming cell (PFC) response to sheep red blood cells (SRBC) in vitro and showed strong mitogenic activity for mouse splenic B-cells but not for splenic T-cells and thymocytes. The enhancement of B-cell proliferation was not mediated by macrophages since their removal did not eliminate the activity. Among the derivatives of catechin examined, (+)catechin (C); (-)epicatechin (EC); (-)-epigallocatechin (EGC); (-)epicatechin gallate (ECg); (-)epigallocatechin gallate (EGCg); and theaflavin digallate (TF3), only the derivatives with the galloyl group (ECg, EGCg, and TF3) displayed significant enhancement of the spontaneous proliferation of B-cells. Structural analogs of the catechin and galloyl groups were also examined in the system. Gallic acid and tannic acid induced some enhancement, but rutin, pyrogallol and caffeine did not. The results indicate that the galloyl group on EGCg was responsible for enhancement. However, the basic conformations of the catechins are also important, because ECg, EGCg, TF3, gallic acid, and tannic acid had quite different potencies to induce B-cell proliferation.

Involvement of antigen and I-J determinants in the induction of effector T suppressor cells by immune B cells

Immune B cells induce effector T suppressor cells in vitro. The B cells act as antigen-presenting cells, and express both I-A and I-J determinants. Antigen and I-J determinants are required for the induction of suppressor T cells by immune B cells, but I-A determinants are not. These findings indicate that precursors of suppressor T cells appear to recognize antigen in the context of I-J determinants on the surface of immune B cells.