Figure 4.

Role of the pulmonary epithelium in cigarette smoke-induced inflammation. The pulmonary epithelium combats leukocyte-derived oxidants and free radicals in cigarette smoke via release of antioxidants. Serine proteases are blocked by low molecular weight inhibitors, SERPINS and TIMPs. Induction of cytokine release by macrophages and epithelial cells and autocrine/paracrine activation of the epithelium stimulates chemokine release and recruitment of monocytes, neutrophils and dendritic cells. In COPD the epithelial defense mechanisms are overwhelmed, leading to increased oxidative stress and proteolytic load, together with leukocyte recruitment, resulting in a chronic cycle of inflammation that may be independent of cigarette smoke exposure.