TNF and bronchitis: Macrophages ingesting exogenous materials produce interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) and, through the activation of signal pathways such as the mitogen-activated protein kinase (MAPK) pathways, expedite the elimination of particulate matter by inducing inflammatory responses; however, excessive or chronic macrophage activation results in inflammatory diseases such as bronchitis or pneumonia [18].