From Suppressor T Cells to Regulatory T Cells: How the Journey that Began with the Discovery of the Toxic Effects of TCDD Led to Better Understanding of the Role of AhR in Immunoregulation

Aryl hydrocarbon receptor (AhR) was identified in the early 1970s as a receptor for the ubiquitous environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), which is a member of halogenated aromatic hydrocarbons (HAHs). TCDD was found to be highly toxic to the immune system, causing thymic involution and suppression of a variety of T and B cell responses. The fact that environmental chemicals cause immunosuppression led to the emergence of a new field, immunotoxicology. While studies carried out in early 1980s demonstrated that TCDD induces suppressor T cells that attenuate the immune response to antigens, further studies on these cells were abandoned due to a lack of specific markers to identify such cells. Thus, it was not until 2001 when FoxP3 was identified as a master regulator of Regulatory T cells (Tregs) that the effect of AhR activation on immunoregulation was rekindled. The more recent research on AhR has led to the emergence of AhR as not only an environmental sensor but also as a key regulator of immune response, especially the differentiation of Tregs vs. Th17 cells, by a variety of endogenous, microbial, dietary, and environmental ligands. This review not only discusses how the role of AhR emerged from it being an environmental sensor to become a key immunoregulator, but also confers the identification of new AhR ligands, which are providing novel insights into the mechanisms of Treg vs. Th17 differentiation. Lastly, we discuss how AhR ligands can trigger epigenetic pathways, which may provide new opportunities to regulate inflammation and treat autoimmune diseases.

Iodine decorated-UiO-67 MOF as a fluorescent sensor for the detection of halogenated aromatic hydrocarbons

An iodine-decorated UiO-67 MOF, UiO-67(I)2 is constructed via the incorporation of iodine groups into the BPDC linker. This decorated MOF exhibited a strong fluorescence response towards halogenated aromatic hydrocarbons (HAHs).

Comparative sorption and desorption of benzo[α]pyrene and 1,2,3-trichlorobenzene by biochar in the presence of dissolved organic matter

Sorption and desorption of benzo[α]pyrene (BaP) and 1,2,3-trichlorobenzene (TrCB) on biochar prepared from maple wood shavings heated at 500°C were studied in the presence of dissolved organic matter (DOM), including citric acid, l-phenylalanine (L-PH), and peptone. Compared to TrCB, BaP exhibited more nonlinear and stronger sorption on biochar. Nonlinearity of the sorption isotherms increased in the presence of DOM. The presence of citric acid enhanced the sorption capacity and desorption hysteresis of BaP and TrCB on biochar mainly due to the strong sorption of citric acid on the biochar surface. Moreover, there were positive relations between the concentration dependent sorption capacity coefficient (K_d) values of BaP and TrCB and the citric acid concentration (P < 0.01). In contrast, peptone reduced the sorption capacity and increased the sorption reversibility because of the partition of BaP and TrCB in the peptone solution. L-PH at 50–200 mg/l also leads to a decrease in the sorption capacity and irreversibility attributed to solubilization, although the sorbed L-PH on the biochar surface can slightly increase the BaP and TrCB sorption. At the same concentration, peptone leads to a higher decrease in the BaP and TrCB sorption than L-PH. Also, negative correlations were found between the K_d values of BaP and TrCB, and the L-PH and peptone concentration (P < 0.05). Our results may help understand the different impacts of DOM on the transport and fate of halogenated aromatic hydrocarbons in aquatic environments polluted with biochars.