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Bisphenol A (BPA) is commonly used in the manufacturing of a wide range of consumer products, including polycarbonate plastics, epoxy resin that lines beverage and food cans, and some dental sealants. Consumption of food and beverages containing BPA represents the primary route of human BPA exposure, which is virtually ubiquitous. An increasing number of studies have evaluated the effects of BPA on immune responses in laboratory animals that have reported a variety of effects some of which have been contradictory. To address the divergent findings surrounding BPA exposure, a comprehensive chronic treatment study of BPA was conducted in Sprague-Dawley rats, termed the Consortium Linking Academic and Regulatory Insights on Toxicity of BPA (CLARITY-BPA). As a participant in the CLARITY-BPA project, our studies evaluated the effects of BPA on a broad range of immune function endpoints using spleen cells isolated from BPA or vehicle treated rats. This comprehensive assessment included measurements of lymphoproliferation in response to mitogenic stimuli, immunoglobulin production by B cells, and cellular activation of T cells, NK cells, monocytes, granulocytes, macrophages and dendritic cells. In total, 630 different measurements in BPA treated rats were performed of which 35 measurements were statistically different from vehicle controls. The most substantive alteration associated with BPA treatment was the augmentation of lymphoproliferation in response to pokeweed mitogen stimulations in 1 year old male rats, which was also observed in the reference estrogen ethinyl estradiol treated groups. With the exception of the aforementioned, the statistically significant changes associated with BPA treatment were mostly sporadic and not dose-dependent with only one out of five BPA dose groups showing a statistical difference. In addition, the observed BPA-associated alterations were mostly moderate in magnitude and showed no persistent trend over the one-year time period. Based on these findings, we conclude that the observed BPA-mediated changes observed in this study are unlikely to alter immune competence in adult rats.

Bisphenol A (BPA) is extensively used in manufacturing of a broad range of consumer products worldwide. Due to its widespread use, human exposure to BPA is virtually ubiquitous. Broad human exposure coupled with a large scientific literature describing estrogenic activity of BPA in animals has raised public health concerns. To comprehensively evaluate the health effects of BPA exposure, a chronic toxicity study using a wide-range of BPA doses (2.5–25000 μg/kg bw/day) was conducted jointly by the NTP, thirteen NIEHS-supported grantees, and the FDA, which is called the Consortium Linking Academic and Regulatory Insights on Toxicity of BPA (CLARITY-BPA). As a participant in the CLARITY-BPA project, the objective of the current study was to evaluate the effects of chronic BPA exposure in Sprague-Dawley rats on the relative number and proportion of defined leukocyte populations in the spleen and the thymus. Toward this end, lymphoid tissues from a total of 641 rats were assayed after being continuously dosed with BPA or controls for up to one year. To comprehensively evaluate the effects of BPA on leukocyte compositions, extensive endpoints that cover major populations of leukocytes were assessed, including B cells, T cells, NK cells, granulocytes, monocytes, macrophages and dendritic cells. In total, of the 530 measurements in BPA-treated rats, 10 measurements were statistically different from vehicle controls and were mainly associated with either the macrophage or dendritic cell populations. Most, if not all, of these alterations were found to be transient with no persistent trend over the one-year time period. In addition, the observed BPA-associated alterations were mostly moderate in magnitude and not dose-dependent. Due to the aforementioned, it is unlikely that the observed BPA-mediated changes alone would adversely affect immune competence.

The homeostasis of peripheral B cell compartment requires lifelong B lymphopoiesis from hematopoietic stem cells (HSC). As a result, the B cell repertoire is susceptible to disruptions of hematopoiesis. Increasing evidence, primarily from rodent models, shows that the aryl hydrocarbon receptor (AHR) regulates hematopoiesis. To study the effects of persistent AHR activation on human B cell development, a potent AHR agonist and known environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was utilized. An in vitro B cell development model system was established by co-culturing human cord blood-derived HSCs with irradiated human primary bone marrow stromal cells. Using this in vitro model, we found that TCDD significantly suppressed the total number of hematopoietic stem and progenitor cells (HSPC) in a concentration-dependent manner. Cell death analysis demonstrated that the decrease in cell number was not due to cytotoxicity by TCDD. In addition, TCDD markedly decreased CD34 expression on HSPCs. Structure-activity relationship studies using dioxin congeners demonstrated a correlation between the relative AHR binding affinity and the magnitude of decrease in the number of HSPCs and CD34 expression, suggesting that AHR mediates the observed TCDD-elicited changes in HSPCs. Moreover, a significant reduction in lineage committed B cell-derived from HSCs was observed in the presence of TCDD, indicating impairment of human B cell development. Similar effects of TCDD were observed regardless of the use of stromal cells in cultures indicating a direct effect of TCDD on HSCs. Collectively, we demonstrate that AHR activation by TCDD on human HSCs impairs early stages of human B lymphopoiesis.

The aryl hydrocarbon receptor (AHR) has been extensively characterized for the essential role it plays in mediating the toxic responses elicited by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Despite similarities across animal species, species-specific differences exist in the profile of toxicity and sensitivity to TCDD owing, in part, to differences in the AHR. Newer reports have implicated the importance of AHR in the development and regulation of the immune system. Our present studies seek to further explore the essential role of AHR in lymphoid tissue composition, B cell function and the immunological responses after TCDD administration using the recently established AHR KO rats. Comprehensive immune cell phenotyping showed a decrease in the CD8+ T cell, CD11c+ populations and an increase in NKT cells in 3-week-old AHR KO rats compared to the WT controls. The lipopolysaccharide-induced IgM response and proliferation was markedly suppressed in the WT but not in the AHR KO B cells in the presence of TCDD. However, the percentage of LPS-activated IgM+ B cells was significantly higher in the AHR KO B cells as compared to that of WT suggesting the role of AHR in regulating the IgM response. The use of an AHR antagonist further alluded to the endogenous role of AHR in regulating B cell responses in the rat. Overall, the studies report for the first time, comprehensive immune cell phenotyping of the AHR KO rat and the endogenous role of AHR in the regulation of B cell function in the rat.