Elucidating the effects of TCDD on the polymorphic human hs1,2 enhancer

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent environmental toxin known to inhibit immunoglobulin (Ig) gene expression in various animal studies. We have identified the mouse 3\u27Ig heavy chain regulatory region (3\u27IgH RR) as a sensitive transcriptional target of TCDD, which may mediate the inhibitory effect of TCDD on Ig expression. Interestingly, the human hs1,2 enhancer is polymorphic and has been associated with a number of autoimmune diseases. Suggesting a species difference, TCDD inhibited mouse hs1,2 enhancer activation and activated basal human hs1,2 (hs-hs1,2) enhancer activity in the mouse B-cell line. The objective of this study was to elucidate the effects of TCDD on the polymorphic human hs1,2 enhancer using a human B-cell line (CL-01) and luciferase reporter constructs regulated by each of the human hs1,2 alleles. Our results verify that TCDD alone activates each of the hu-hs1,2 alleles. Surprisingly, B-cell stimulation through the Toll-like receptors (TLR) 7, 8, and 9, and the AhR antagonist inhibited basal activity of the hu-hs1,2 alleles and TCDD co-treatment reversed TLR-induced inhibition. Contrary to this, TLR stimulates IgM secretion as well as class switching to IgG secretion. These results suggest that the hu-hs1,2 enhancer may be a negative regulator of 3\u27IgH RR activity and Ig expression