Objective & Clinical Relationship: Our long-term goal is to identify the alcohol-mediated tissue injury mechanisms observed in individuals with alcohol-use disorders (AUDs) so that better early biomarkers of injury can be developed leading to enhanced approaches to minimize pathogen susceptibility and prevent the high costs of pneumonia. Research Design & Methodology: Alcohol abuse causing increased susceptibility to pneumonia has been known for over 200 years. NIAAA publications state that hospitalized individuals with alcohol use disorders (AUDs) have a 3-fold risk of mortality from pneumonia. Alcohol modulates both the innate and adaptive immune systems of the lung resulting in increased susceptibility and decreased resolution of infection. For 20 years, our research group has been a recognized leader in studying the chronic effects of alcohol on the innate immunity provided by the mucociliary transport apparatus. Because the majority (>90%) individuals with AUDs smoke cigarettes, we have chosen to take the public health relevant approach of studying the combination lung injury effects of both cigarettes and alcohol. In our previous funding cycle, we identified that the lungs represent a unique environment for the formation of stable malondialdehyde-acetaldehyde protein adducts (MAA adducts), but only under conditions of combined cigarette smoke and alcohol exposure. These MAA adducts cause airway epithelial cell cilia slowing and impair the innate pathogen clearance from the lung. Our published and preliminary data demonstrate that surfactant protein D (SPD) is a major lung protein that gets adducted when lung aldehyde concentrations are elevated during combined smoke and alcohol exposure. Using human samples derived from the NIAAA-supported Colorado Pulmonary Alcohol Research Consortium, we have found that MAA adducts are detected in the lung lavage macrophages and fluid only in individuals with AUDs who also smoke. We have observed that the AUD smokers have decreased lung mucosal sIgA and that MAA adduct treatment of airway epithelium blocks transcytotic processing of sIgA mucosal secretion. Because of these important and novel observations, we now propose to extend our research on the pathogenesis of the MAA adduct to lung macrophages, mucosal sIgA, and SPD. Our overall hypothesis is that MAA adducts uniquely form in the lungs of individuals who consume both alcohol and smoke cigarettes, leading to alterations in innate lung defense. We will investigate this hypothesis through 3 aims: Aim 1: MAA adducted lung SPD (MAA-SPD) binds to lung macrophages via scavenger receptor A leading to alterations in macrophage function; Aim 2: MAA-SPD prevents sIgA mucosal secretion in lung by altering epithelial cell processing of dimerized IgA; and Aim 3: MAA adduction of SPD decreases its anti-microbial action.