Emphysema is caused by the cigarette smoke (CS)-induced destruction of alveolar wall septa, and CS is the main risk factor for chronic obstructive pulmonary disease (COPD). To study the mechanisms of response to this insult, we focused on oxidant-induced lung injury and the potential role of nuclear erythroid 2-related factor-2 (Nrf2), which is a key regulator of the antioxidant defense system. We studied the protective role of N-acetylcysteine (NAC) against the injury of alveolar type II (ATII) cells induced by CS in vivo and in vitro. ATII cells were isolated and purified using magnetic MicroBeads (Miltenyi Biotec, Auburn, CA) from Nrf2 2/2 mice and wild-type mice. We analyzed pulmonary injury, inflammation, glutathione (GSH) concentrations, the expression of glutathione cysteine ligase catalytic subunit mRNA, glutathione cysteine ligase modifier subunit mRNA, and glutathione reductase mRNA, and Nrf2, heme oxygenase-1, and nicotinamide adenine dinucleotide phosphate-reduced:quinone oxireductase levels by Western blotting, TUNEL assay, and immunocytofluorescence for 4-hydroxynonenal as a marker of oxidative stress. We found that CS induced greater injury in ATII cells obtained from Nrf2 2/2 mice than from wild-type mice. Furthermore, NAC attenuated the injuries by CS in ATII cells obtained from wild-type mice both in vivo and in vitro. Moreover, NAC decreased the injury of ATII cells obtained from Nrf2 2/2 mice. Our results suggest that Nrf2-GSH signaling is important for the protective activity of NAC. In addition, in ATII cells deficient in Nrf2, this compound can provide partial protection through its reactive oxygen species-scavenging activities. Targeting the antioxidant system regulated by Nrf2 may provide an effective strategy against lung injury in COPD.Keywords: murine alveolar type II cells; lung; Nrf2; NAC; cigarette smoke Chronic obstructive pulmonary disease (COPD) is currently the third-leading cause of death in the United States (1, 2), and mortality rates continue to rise. Emphysema is caused by the destruction of the alveolar wall septa, which is brought about by cigarette smoke (CS) and its associated lung inflammation (3, 4). CS is a complex mixture of different chemicals, including free radicals and other oxidants. Cell death (both apoptosis and necrosis) by CS has been shown to produce oxidant injury both in vitro and in vivo (5-7). However, the exact mechanism underlying CS-induced alveolar epithelial cell death in COPD remains unclear.The nuclear erythroid 2-related factor-2 (Nrf2) transcription factor is a key determinant of COPD susceptibility (8-11), and one of the critical regulators of cellular redox status (12, 13). Nrf2 is required for the constitutive and inducible expression of the glutathione cysteine ligase catalytic subunit (GCLC) and the glutathione cysteine ligase modifier subunit (GCLM), which are required for glutathione (GSH) synthesis (14). Nrf2 also regulates the expression of other cellular antioxidant genes, such as heme oxygenase-1 (HO-1) and nicotinamide adenine din...