The aim of this review was to delineate how the current research involving the role of AhR in immunoregulation, specifically T cells, and its repercussion on the regulation of inflammatory and autoimmune diseases, originated from the field of immunotoxicology in the late 1970s and the early 1980s, when immunologists discovered that TCDD, an environmental pollutant, suppressed the immune response. The gene discussed is AHR; the disease is autoimmune disease.