Smoking-Related Interstitial Fibrosis and Smoker's Macrophages.

Smoking-related interstitial lung diseases (SRILDs) are a group of heterogeneous diffuse pulmonary parenchymal diseases associated with tobacco exposure. Smoking-related interstitial fibrosis (SRIF) is relatively recent, a pathologically defined form of SRILDs. SRIF is characterized by the accumulation of macrophages in the alveolar spaces, which is associated with interstitial inflammation and fibrosis. The macrophages frequently contain light brown pigment and are called 'smoker's macrophages'. Patients with SRIF who have clinical evidence of interstitial lung disease are most commonly relatively young, heavy smokers with abnormalities on chest computed tomography showing ground-glass opacities, peripheral consolidation, and reticulation. Although SRIF is caused by cigarette smoking, the exact pathophysiological mechanisms by which smoking causes this type of interstitial fibrosis remain unknown. The degree of fibrosis and appearance of macrophage aggregates are important points of distinction when evaluating and diagnosing SRIF. Macrophage heterogeneity, particularly the activation and function of monocyte-derived alveolar macrophages (Mo-AMs) and interstitial macrophages (IMs), has important implications for the pathogenesis of SRIF and developing treatments. Further researches focused on smoker's macrophages are needed to understand of the pathogenesis of SRIF.