Background: Chronic obstructive pulmonary disease (COPD) is a global health problem. Currently, there is a lack of knowledge about the pathobiology of this disease and available therapies are ineffective. Cigarette smoking is the leading cause of COPD; however, not all smokers develop COPD. Exacerbations of COPD caused by microbes are common and detrimental. Approximately 20-50% of patient exacerbations are caused by bacterial colonization in the lower airways. It is generally accepted that epigenetic mechanisms, especially DNA methylation, play an important role during progression of COPD. Thus, we hypothesized that DNA methylation patterns vary significantly following smoke exposure and during exacerbations caused by bacterial infections. To test our hypothesis, we used an in vitro study model that mimics COPD exacerbations and performed extensive studies to understand the role of CpG promoter methylation of NF-