AHR and autoimmune disease: The combination of epidemiological data that associated PM, as well as cigarette smoke, with increased risk and/or exacerbated autoimmune diseases and the in vitro studies in mice that demonstrated PM and its chemically-extracted organic fraction (63, 100), cigarette smoke extract (63), individual PAHs (63), and synthetic PAH mixtures (100), enhanced Th17 differentiation suggest that PAHs present in PM are candidate components that may activate the AHR, shift T cell balances, and alter autoimmune disease status.