MOLECULAR MECHANISM OF IMMUNOTOXIC ACTION OF TCDD & DTT

一些环境污染物如2.3.7.8

Some environmental contaminants such as 2.3.7.8 tetrachlorodibenzoparadioxin (TCDD) and 1.1.1-trichloro-2-(2- chlorophenyl)-2-(4-chlorophenyl)ethane (o,p'DTT), are known to have steroidal actions as well as immunotoxic actions in animals and humans. These compounds bind to intracellular receptor proteins similar to those for glucocorticoids and estrogens. Since the immune system plays a crucial role in host resistance and homeostasis, the immunomodulation induced by the xenobiotics may be the basis for adversed health effects. Monocytes/macrophages have various key functions in initiating the immune regulation, mediating through antigen presentation, monokine production, and formation of arachidonate metabolites, and these functions are known to be affected by glucocorticoids and estrogens. In the projects proposed herein, we aim to investigate the molecular mechanism of actions of steroids and xenobiotics on function of monocytes/macrophages and subsequently, of cell mediated immunity. The specific aims are to examine (a) whether these xenobiotics and steroids bind to the same or different receptors, (b) whether they induce or block the synthesis of second messenger proteins of steroids, (c) what are their actions on the gene expression of IL 1, TNF, HLA-DR and lipocortin and (d) whether these effects on IL 1, TNF, HLA-DR and lipocortin are attributed to alteration of arachidonate metabolism or of gene regulation by the xenobiotic- receptor complex or both. Xenobiotics and steroids will be incubated in vitro with fractionated human peripheral monocytes/macrophages in the absence and presence of specific and nonspecific activators such as gamma-lFN, LPS and phorbol esters. Metabolites of arachidonate will be quantitatively analyzed by high performance liquid chromatography. The binding analysis will be performed by competitive ligand binding assays. Identification of newly induced proteins will be carried out by two dimensional electrophoresis using (35S)methionine and their biological actions on monocytes and T lymphocytes will be examined. The regulation of IL 1, TNF, lipocortin (putative second messenger of glucocorticoids) and HLA-DR gene expression will be investigated by the Northern Blot using their cDNA clones as probes. To exploit not only the mechanism of immunotoxicity of xenobiotics but also the mechanism of immunoregulation leading to the immunosuppression (acquired immune deficiency), we propose to establish the mechanism of action of xenobiotics on the biochemical and cellular functions of monocytes/macrophages.