Acute ethanol intoxication suppresses the host immune responses against Streptococcus pneumoniae. As interleukin 17 (IL-17) is a critical cytokine in host defense against extracellular pathogens, including S. pneumoniae, we hypothesized that ethanol impairs mucosal immunity against this pathogen by disrupting IL-17 production or IL-17 receptor (IL-17R) signaling. A chronic ethanol feeding model in simian immunodeficiency virus (SIV)-infected rhesus macaques and acute ethanol intoxication in a murine model were used. Transcriptome analysis of bronchial brushes in the nonhuman primate model showed downregulation of the expression of IL-17-regulated chemokines in ethanol-fed animals, a finding also replicated in the murine model. Surprisingly, recombinant CXCL1 and CXCL5 but not IL-17 or IL-23 plus IL-1 rescued bacterial burden in the ethanol group to control levels. Taken together, the results of this study suggest that ethanol impairs IL-17-mediated chemokine production in the lung. Thus, exogenous luminal restoration of IL-17-related chemokines, CXCL1 and CXCL5, improves host defenses against S. pneumoniae.
Bacterial pneumonia is a complication of ethanol abuse, and this susceptibility was documented both in animal models and in human studies more than a century ago (1, 2). Excessive ethanol consumption remains a public health problem responsible for approximately 79,000 deaths in the United States each year and for an estimated economic cost of $223.5 billion in 2006 (3).Streptococcus pneumoniae is a Gram-positive bacterium and the leading etiology of community-acquired pneumonia, especially in older adults and alcoholic patients. Innate immune responses are important to control infections by S. pneumoniae, as evidenced by the roles of Toll-like receptors, MyD88, and IRAK4 in both humans and animal models (4, 5). More recently, evidence has emerged to support the fact that interleukin 17 (IL-17) plays a critical role in the regulation of S. pneumoniae colonization and infection. IL-17 and CD4 ϩ T cells, and specifically the Th17 subset, are important for clearance of nasopharyngeal colonization with S. pneumoniae (a prerequisite of pneumococcal pneumonia) during primary and secondary infection (6, 7).IL-17 is a cytokine produced by activated CD4 ϩ T cells and innate lymphocytes (␥␦ ϩ T cells, NK cells, and innate lymphoid cells) and drives inflammation and autoimmunity (8). In the lung, the airway epithelium plays an important role in orchestrating the production of C-X-C chemokines, and these cells express both IL-17RA and IL-17RC and can produce both C-X-C chemokines and granulocyte colony-stimulating factor (G-CSF) in response to IL-17, leading to neutrophil recruitment in vivo (9-11).As the lung epithelium is a major site of chemokine production during bacterial pneumonia (12), we examined the effect of ethanol on gene expression in the airway epithelium during experimental S. pneumoniae infection in a nonhuman primate model of ethanol consumption and pneumococcal infection (13,14). We analyzed bronchial b...