– 1,2,3,6,7,8-Hexachlorodibenzo-p-dioxin, a polychlorinated dibenzodioxin (PCDD), acts as an agonist for the aryl hydrocarbon receptor (AhR; EC50s = 5.4 and 9.3 nM at 4 and 8 h, respectively, in a reporter assay). It has been observed to reduce antibody production against sheep red blood cells in mice at doses of 0.5 and 2 µg/kg. This compound has been detected in animal feed and in the vicinity of municipal waste incinerators.