TNF and type 2 diabetes mellitus: In our previous studies, the expression in inflammatory genes in BAT (such as TNFα, IL-6, and F4/80 etc.)increased in response to PM2.5 inhalation(Liu et al., 2014a), whereas, TNFα implicates a link between adiposity and the development of insulin resistance and is an important contributor to the pathogenesis of type 2 diabetes (Hotamisligil et al., 1993).