Synergistic Immunosuppression by PAHs and Arsenite

描述（由申请人提供）：这些研究的目的是评估与多环芳烃（PAHs）和亚砷酸钠（As+3）联合暴露相关的小鼠和人类免疫抑制机制。众所周知，免疫系统的抑制与抵抗感染和癌症的能力下降有关。初步数据表明，小鼠体内通过食物和饮用水暴露于As+3和PAHs时，表现出协同免疫抑制作用。我们还提供了初步数据，表明在饮用水中发现的与环境相关的钠As+3水平下，人外周血单个核细胞（hbmc）会受到免疫抑制。PAHs也增加了As+3诱导的免疫抑制量。因此，了解这些药物单独或联合暴露时产生免疫抑制的机制非常重要。在本应用中要测试的中心假设是多环芳烃和As+3通过DNA损伤和修复途径产生协同免疫抑制。重要的是建立动物模型来研究协同免疫抑制，并进行与人类暴露相关的机制研究。这些研究将确定，在小鼠模型中，饮用水中的砷+3和饮食中的多环芳烃（存在于我们呼吸的空气和吃的食物中）共同暴露是否会比之前发现的单独暴露这两类物质产生更大的抑制作用。我们将确定这些相互作用的潜在生化机制，我们将确定饮用水中存在的Zn+2是否可以保护小鼠免受As+3的暴露。最后，由于我们发现人类血液T淋巴细胞对美国和世界其他地方许多人群饮用水中存在的低浓度As+3极其敏感，我们将确定不同人群（不同年龄和种族的男性和女性）对这些暴露的敏感性。我们将获得这些个体的外周血细胞，以确定他们的免疫反应是否被单独或联合给予As+3和PAH体外抑制。这些研究的结果将对了解调节人体免疫系统的环境因素做出重要贡献，并可能为砷+3饮用水暴露的干预提供方法。

DESCRIPTION (provided by applicant): The purpose of these studies is to evaluate the mechanisms of immunosuppression in mice and humans associated with combined exposures to polycyclic aromatic hydrocarbons (PAHs) and sodium arsenite (As+3). Suppression of the immune system is known to be associated with a decreased ability to fight infections and cancer. Preliminary data is presented that mice demonstrate synergistic immunosuppression when exposed to As+3 and PAHs in vivo through their food and drinking water. We also present preliminary data demonstrating that human peripheral blood mononuclear cells (HPBMC) are immunosuppressed at environmentally relevant levels of sodium As+3 found in drinking water. PAHs were found to increase the amount of As+3 induced immune suppression as well. Therefore, it is important to understand the mechanism(s) of immunosuppression produced by these agents when exposures occur alone or in combination. The central hypothesis to be tested in this application is that PAHs and As+3 produce synergistic immunosuppression through DNA- damaging and repair pathways. It is important to develop animal models to study synergistic immunosuppression and to pursue mechanistic studies of relevance to human exposures. These studies will determine whether co-exposures from As+3 in drinking water and PAHs in the diet (which are present in the air we breathe and the food we eat) in mouse models result in greater suppression than has previously been found for either class of agents on their own. We will determine the biochemical mechanisms potentially responsible for these interactions, and we will determine whether Zn+2 present in drinking water can protect mice from As+3 exposures. Finally, because we found that human blood T lymphocytes are extremely sensitive to low concentrations of As+3 that are present in drinking water in many populations in the U.S. and elsewhere in the world, we will determine the sensitivities of various humans (males and females of different ages and ethnicities) to these exposures. We will obtain peripheral blood cells from these individuals to determine whether their immune response are suppressed by As+3 and PAH given in vitro alone or in combination. The results of these studies will make an important contribution to understanding environmental agents that modulate the human immune system and perhaps provide an approach to intervention for As+3 drinking water exposures. PUBLIC HEALTH RELEVANCE: The purpose of these studies is to evaluate the mechanisms of immunosuppression in mice and humans associated with combined exposures to polycyclic aromatic hydrocarbons (PAHs) and sodium arsenite (As+3). Suppression of the immune system is known to be associated with a decreased ability to fight infections and cancer. Preliminary data is presented that mice demonstrate synergistic immunosuppression when exposed to As+3 and PAHs in vivo. We also present preliminary data demonstrating that human peripheral blood mononuclear cells (HPBMC) are extremely sensitive to T cell immunosuppression by environmentally relevant levels of exposure to sodium As+3 and that PAHs interact significantly with As+3 as well. Therefore, it is important to understand the mechanism(s) of immunosuppression produced by these agents when exposures occur alone or in combination. The central hypothesis to be tested in this application is that PAHs and As+3 produce synergistic immunosuppression through genotoxic pathways resulting from DNA adduct formation and inhibition of DNA repair. It is important to develop in vivo models to study synergistic immunosuppression and to pursue mechanistic studies of relevance to human exposures. In SA1 we will utilize our established mouse model for studies of the combined effects of PAHs, on the T-dependent antibody response (TDAR) in murine spleen and pre-B and granulocyte/monocyte (GM) progenitor cell activity of bone marrow (BM) cells. We provide exciting new in vitro data demonstrating that Zn+2 can overcome the immunosuppression (spleen TDAR) produced by exposures to As+3, perhaps based on the zinc finger protein theory discussed below. We know that genotoxicity and p53 signaling are important mechanisms of immunosuppression produced by PAHs, and perhaps for As+3 in mice. Therefore, we will examine the p53- dependence of spleen and BM suppression using p53 null mice. In SA2 we will determine whether the mechanism of synergy is due to inhibition of DNA repair. Our preliminary data show that As+3 inhibits DNA repair and that co-exposures to PAHs and As+3 may lead to an increase in PAH bulky and oxidative stress adducts resulting in increased p53 signaling. In our previous studies we showed that As+3 binds to the zinc finger proteins, PARP-1 and XPA, leading to inhibition of DNA repair in both Nucleotide Excision Repair (NER) and Base Excision Repair (BER) pathways. We will test the hypothesis that Zn+2 supplementation can reverse the effects of As+3 in vivo in mice. In SA3, we will build on our preliminary data that human T cells are inhibited by low nanomolar (nM) concentrations of As+3 exposures in vitro. We will also examine the ability of Zn+2 to reverse this immunosuppression in HPBMC in vitro. Because we have found that there are significant inter-individual differences, we will perform initial characterization of As+3 and PAH exposure in 150 different individuals. Completion of these studies will yield critical new data relating to our central hypothesis and will determine th potential sensitivities of the human immune system to binary exposures of PAHs and As+3.