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Interaction with Epithelial Cells Modifies Airway Macrophage Response to Ozone
Bauer, R., L. Mueller, L. Brighton, K. Duncan, AND I. Jaspers. Interaction with Epithelial Cells Modifies Airway Macrophage Response to Ozone. AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGY. American Thoracic Society, New York, NY, 52(3):285-294, (2015).
Inhalation of 03 causes immediate nociceptive decreases in lung function and increased airway inflammation that can exacerbate preexisting diseases, such as asthma and chronic obstructive pulmonary disease (I). Despite regulations to reduce ambient 03, in 2008 approximately 36.2% of the U.S. population lived in counties that did not meet the National Ambient Air Quality 8-hour 03 standard (0.075ppm averaged per 8 hours) (2). Though the adverse health effects of 03 are well known, the cellular mechanisms by which 03 alters immune responses in the lung remain unclear. The induction of airway inflammation following 03 exposure suggests an ongoing innate immune response in the lung. Since 03 is an oxidant gas, the innate immune response to 03 is not likely mediated by recognition through discreet receptors (3). Rather, 03 reacts with components of the airway lining fluid and cellular membrane, such as surfactants and phospholipids,generating reactive intermediates that damage the respiratory epithelium, inducing endogenous danger signals that initiate innate immune responses (1, 4, 5). For example, short fragments of hyaluronic acid (HA), an extracellular matrix glycosaminoglycan produced by airway epithelial cells, have been shown to serve as danger signals in the response to 03 (6, 7). HA fragments induce airway hyperreactivity and activate inf1ammatory responses via pattern recognition receptors such as CD44 (6). Quantities of HA are elevated in the airways of mice and atopic asthmatics after in vivo 03 exposure (6, 8).
The initial innate immune response to ozone (03) in the lung is orchestrated by structural cells, such as epithelial cells, and resident immune cells, such as airway macrophages (Macs). We developed an epithelial cell-Mac coculture model to investigate how epithelial cell-derived signals affect Mac response to 03. Macs from the bronchoalveolar lavage (BAL) of healthy volunteers were cocultured with the human bronchial epithelial (16HBE) or alveolar (A549) epithelial cell lines. Cocultures, Mac monocultures, and epithelial cell monocultures were exposed to 03 or air and Mac immunophenotype , phagocytosis, and cytotoxicity were assessed. Quantities of hyaluronic acid (HA) and IL-8 were compared across cultures and in BAL fluid from healthy volunteers exposed to 03 or air for in vivo confirmation. We show that Macs in coculture had increased markers of alternative activation, enhanced cytotoxicity, and reduced phagocytosis compared with Macs in monoculture that differed based on roculture with A549 or 16HBE. Production of HA by epithelial cell monocultures was not affected by 03, but quantities of HA in the in vitro coculture and BAL fluid from volunteers exposed in vivo were increased with 03 exposure, indicating that 03 exposure impairs Mac regulation of HA. Together, we show epithelial cell-Mac coculture models that have many similarities to the in vivo responses to 03, and demonstrate that epithelial cell-derived signals are important determinants of Mac immunophenotype and response to 03.