XRE (Xenobiotic Response Element) is a conserved cisregulatory DNA sequence specifically recognized and bound by the ligandactivated aryl hydrocarbon receptor (AhR)aryl hydrocarbon receptor nuclear translocator (ARNT) heterodimer. Upon AhR activation by xenobiotics, environmental pollutants, or endogenous ligands, the AhRARNT complex translocates into the nucleus, interacts with XRE motifs, and initiates transcription of downstream target genes.XRE(s) are highly conserved in species as it has only eight specific sequences found so far in humans, mice, and rats. Inhalation of toxicants like dioxins, gaseous industrial effluents, and smoke from burning fuel and tobacco leads to predominant damage to the lungs.