1,2,3,4,7,8,9-Heptachlorodibenzofuran (1,2,3,4,7,8,9-HpCDF) is a chemical compound known for inducing the expression of CYP1A1 and CYP1B1 genes in human peripheral blood lymphocytes, while also enhancing the expression of the aromatic hydrocarbon receptor repressor (AhRR). In isolated human peripheral blood lymphocytes, it boosts ethoxyresorufin-O-deethylase (EROD) activity—a marker for CYP1A1 activity—in a concentration-dependent manner. Additionally, 1,2,3,4,7,8,9-HpCDF exhibits immunosuppressive properties, reducing the number of plaque-forming cells in mouse spleens and increasing aromatic hydrocarbon hydroxylase (AHH) activity in the liver microsomes of mice injected with sheep red blood cells. This compound is pertinent to research in the fields of immunology, metabolic diseases, and environmental toxicology.