Effects of 2,3,7,8-TCDD and PCB 126 on human thymic epithelial cells in vitro

Abstract

2,3,7,8-Tetrachloro-dibenzo- p-dioxin (TCDD) is a ubiquitously distributed xenobiotic. The adverse effects of TCDD on the mammalian immune system have been studied for decades, but it is still unclear whether TCDD has direct effects on T-lymphocytes or whether it acts via the thymic microenvironment. We have studied the effects of TCDD on primary cultures of human thymic epithelial cells (TEC) focusing on differentiation markers, integrins and adhesion molecules involved in cell-cell and in cell-matrix interactions. TEC were treated with TCDD at concentrations of 0.001, 0.01, 0.1, 1.0 or 10.0 nM or with 100 nM PCB 126 (3,3',4,4',5-pentachlorobiphenyl) for 3 days, and were then analysed by flow cytometry for expression of surface antigens using monoclonal antibodies against Hassall's bodies (TE-8, TE-16) or against surface structures such as CD29, CD49b, CD49e, CD49f, CD51, CD54, CD58, CD61 and CD106. At TCDD concentrations as low as 0.01 nM we found a significant increase in terminally differentiated, TE-16-positive TEC; at a ten-fold greater concentration the number of cells marked with the TE-8 antibody was also increased. With both markers the most pronounced effect (approximately +15%) was observed at 1 nM TCDD. An increase of cells expressing the integrin alpha-chains CD49b, CD49e and CD51 as well as CD54 was observed at concentrations of 0.1 nM TCDD or higher. The proportion of cells expressing CD106 or CD49f decreased significantly upon treatment with TCDD. No effects on the integrin beta-chains CD29 and CD61 could be detected. Overall, PCB 126 induced similar changes to TCDD. In summary, TCDD and a coplanar PCB induced terminal differentiation of human TEC along with changes of integrins and other adhesion molecules. These receptors and their interplay with the extracellular matrix have key functions in the maturation of T-lymphocytes and it is plausible that their alteration would be involved in TCDD-induced immunotoxicity.

The aryl hydrocarbon receptor (AhR) pathway as a regulatory pathway for cell adhesion and matrix metabolism

“…1). In the monocytic leukemia THP-1 cell line, mRNA levels of β7 and α5 integrins are increased following AhR activation, whereas expression of α6 is decreased in human thymic epithelial cells (23). The increase in β7 integrin is also observed in primary human macrophages and developing T-lymphocytes (24,25).…”

“…(1) AhR pathway alters the expression of ECM proteins, including types I and IV collagen and fibronectin in fetal heart and marmoset myocardium and thymocytes (17–20). (2) Expression of several integrin subtypes, including the β7 subtype is altered following AhR signaling in cytotoxic T-cells (22), thymic epithelial cells (23), macrophages (24), T-lymphocytes (25) and human amniotic epithelial cells (26). (3) Focal adhesion kinase (FAK) phosphorylation in HUVECs (29).…”

The aryl hydrocarbon receptor links integrin signaling to the TGF-β pathway

“…The TGF-β pathway, in turn, is controlled by the activity of αv integrins in glioma cells (11). AhR has been described as a regulator of the composition of integrins at the cell surface (13,(20)(21)(22)(23), but inhibitory effects of AhR on FAK phosphorylation, a central mediator of integrin signaling, have also been observed (14,24). These findings provided the rationale for the present study, which aimed at elucidating a possible link between the AhR and integrin signaling pathways in modulating the activity of the TGF-β pathway in glioblastoma.…”

Contributions of Nonhematopoietic Cells and Mediators to Immune Responses: Implications For Immunotoxicology

“…TSC function within the realm of toxicology has intensely focused on the role of the aryl hydrocarbon receptor (AhR) and toxicity due to AhR ligation. Early evidence and follow-up studies suggest that AhR agonists, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), affect thymic epithelial cells but not thymocytes nor thymic dendritic cells (DCs) to cause thymic involution (Camacho et al, 2005;De Heer et al, 1994;De Waal et al, 1992;Greenlee et al, 1985;Kremer et al, 1994;Laiosa et al, 2003;Riecke et al, 2003). Since then, reports found precursor (Fine et al, 1990) or hematopoietic cells (including thymocytes) (Kamath et al, 1997;Kurl et al, 1993;Laiosa et al, 2010;McConkey et al, 1988;Rhile et al, 1996;Staples et al, 1998) to be the direct targets for AhR-mediated thymic involution.…”