Cigarette smoke contributes to many diseases. The actions of second and third hand smoke, which have implications for non-smokers and the very young, are just beginning to be appreciated. The overarching hypothesis of this project is that cigarette smoke has different injurious actions on alveolar cells based on chronological age. The purpose here was to learn more about the susceptibility of alveolar cells to cigarette smoke extract (CSE)- induced injury by performing studies on pulmonary alveolar and endothelial cells derived from neonatal, young, and old rats. The aims involved: 1. Developing cell culture models to study age-related effects of cigarette smoke on alveolar type I cells and microvascular endothelial cells from the lung, and 2. Using these models to examine the effects of CSE on markers of oxidative stress, inflammation and aging in alveolar cells harvested from neonatal, young and old rats. Descriptive and experimental studies involved using a variety of cell culture, biochemical and molecular techniques, including gene expression arrays. The most significant findings were that: 1. primary proliferating alveolar type I cells were used to develop novel cell culture model systems, including single culture, co-culture and three-dimensional cultures that were used to study the effects of CSE; 2. Hydrogen peroxide production by endothelial cells was markedly reduced by co-culturing with AT I cells; 3. Gene expression profiling of oxidative stress-specific pathways suggest that genes responsible for both stopping production of H2O2 or mopping-up H2O2 are involved; and 4. Cigarette smoke shortens telomeres of cells from neonates, but unexpectedly preserves telomere length of cells from young and old rats. Data from telomeric pathway-specific gene expression arrays suggest that there are age-related differences in response to gene expression to CSE. The significant conclusions are: 1. Contrary to prior observations, alveolar type I cells demonstrate prolonged proliferative capacity; 2. Alveolar type I cells likely play an important role in ameliorating CSE-induced oxidative stress; and 3. Neonatal alveolar cells may be more susceptible to the deleterious effects of CSE including telomere shortening. These novel model systems and observations provide new ways to study cigarette smoke-associated lung dysfunction.