Superantigen-primed T cells exposed to 2,3,7,8–tetrachlorodibenzo-p-dioxin (TCDD) replicate poorly following recall encounter

AhR Activation Leads to Massive Mobilization of Myeloid-Derived Suppressor Cells with Immunosuppressive Activity through Regulation of CXCR2 and MicroRNA miR-150-5p and miR-543-3p That Target Anti-Inflammatory Genes

The compound 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an environmental contaminant, is a potent ligand for aryl hydrocarbon receptor (AhR). In the current study, we made an exciting observation that naive C57BL/6 mice that were exposed i.p. to TCDD showed massive mobilization of myeloid-derived suppressor cells (MDSCs) in the peritoneal cavity. These MDSCs were highly immunosuppressive and attenuated Con A-induced hepatitis upon adoptive transfer. TCDD administration in naive mice also led to induction of several chemokines and cytokines in the peritoneal cavity and serum (CCL2, CCL3, CCL4, CCL11, CXCL1, CXCL2, CXCL5, CXCL9, G-CSF, GM-CSF, VEGF, and M-CSF) and chemokine receptors on MDSCs (CCR1, CCR5, and CXCR2). Treatment with CXCR2 or AhR antagonist in mice led to marked reduction in TCDD-induced MDSCs. TCDD-induced MDSCs had high mitochondrial respiration and glycolytic rate and exhibited differential microRNA (miRNA) expression profile. Specifically, there was significant downregulation of miR-150-5p and miR-543-3p. These two miRNAs targeted and enhanced anti-inflammatory and MDSC-regulatory genes, including IL-10, PIM1, ARG2, STAT3, CCL11 and its receptors CCR3 and CCR5 as well as CXCR2. The role of miRs in MDSC activation was confirmed by transfection studies. Together, the current study demonstrates that activation of AhR in naive mice triggers robust mobilization of MDSCs through induction of chemokines and their receptors and MDSC activation through regulation of miRNA expression. AhR ligands include diverse compounds from environmental toxicants, such as TCDD, that are carcinogenic to dietary indoles that are anti-inflammatory. Our studies provide new insights on how such ligands may regulate health and disease through induction of MDSCs.

Computational prediction and in vitro validation of VEGFR1 as a novel protein target for 2,3,7,8-tetrachlorodibenzo-p-dioxin

The toxic manifestations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an environmental contaminant, primarily depend on its ability to activate aryl hydrocarbon receptor (AhR), which is a ligand-dependent transcription factor belonging to the superfamily of basic-helix-loop-helix DNA-binding proteins. In the present study, we aimed to identify novel protein receptor targets for TCDD using computational and in vitro validation experiments. Interestingly, results from computational methods predicted that Vascular Endothelial Growth Factor Receptor 1 (VEGFR1) could be one of the potential targets for TCDD in both mouse and humans. Results from molecular docking studies showed that human VEGFR1 (hVEGFR1) has less affinity towards TCDD compared to the mouse VEGFR1 (mVEGFR1). In vitro validation results showed that TCDD can bind and phosphorylate hVEGFR1. Further, results from molecular dynamic simulation studies showed that hVEGFR1 interaction with TCDD is stable throughout the simulation time. Overall, the present study has identified VEGFR1 as a novel target for TCDD, which provides the basis for further elucidating the role of TCDD in angiogenesis.

The effects of vitamin E on NK cell activity and lymphocyte proliferation in treated mice by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The study was conducted to investigate the effects of vitamin E on NK cell activity and lymphocyte proliferation in tr eated female mice by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In chronic TCDD trial, 45 mice were divided into 5 groups, and the levels of TCDD and vitamin E were 0 and 0, 100 and 0, 100 and 20, 100 and 100, and 100 ng/kg/d and 500 mg/kg/d, respectively. In acute TCDD trial, 24 mice were divided into three groups, and the levels of TCDD and vitamin E were 0 and 0, 30 and 0, and 30 microg/kg and 100 mg/kg, respectively. The results showed chronic TCDD-treatment caused decrease tendencies of spleen NK cell activity and lymphocyte proliferation, and vitamin E 100mg/kg alleviated the decreases tendencies caused by chronic TCDD-treatment, and the lymphocyte proliferation in the group given vitamin E 100mg/kg was significantly higher than that of the chronic TCDD-treated group. Acute TCDD-treatment suppressed the NK cell activity and lymphocyte proliferation, and vitamin E 100mg/kg significantly alleviated the decrease caused by acute TCDD-treatment. These results suggested that TCDD resulted in immunotoxicity, and the toxicity of acute TCDD-treatment was severe compared with chronic TCDD, while vitamin E alleviated the immunotoxicity from TCDD.