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Effect of Concentrated Ambient Particles on Macrophage Phagocytosis and Killing of Streptococcus pneumoniae

Department of Environmental Health, Harvard School of Public Health; and Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts

Correspondence and requests for reprints should be addressed to Dr. Lester Kobzik, Department of Environmental Health, Molecular and Integrative Physiological Sciences Program, Harvard School of Public Health, 665 Huntington Ave, BLDG 2, Rm. 221, Boston, MA 02115. E-mail: lkobzik{at}hsph.harvard.edu

Particulate air pollution is linked to increased pneumonia epidemiologically and diminished lung bacterial clearance experimentally. We investigated the effect of concentrated ambient particles (CAPs, PM_2.5) on the interaction of murine primary alveolar macrophages (AMs) and the murine macrophage cell line, J774 A.1, with Streptococcus pneumoniae. We found that CAPs increased binding of bacteria by both primary AMs and J774 cells (66.7 ± 10.6% and 58.9 ± 4.0%, respectively, n = 4). In contrast to bacterial binding, CAPs decreased internalization in both AMs and J774 (55.4 ± 8.5% and 54.7 ± 5.1%, respectively, n = 4). The rate of killing of internalized bacteria was similar, but CAPs caused a decrease in the absolute number of bacteria killed by macrophages, mainly due to decreased internalization. Additional analyses showed that soluble components of CAPs mediated the enhanced binding and decreased internalization of S. pneumoniae. Chelation of iron in soluble CAPs substantially reversed, while addition of iron as ferric ammonium citrate restored inhibition of phagocytosis of S. pneumoniae in vitro. The results identify phagocytic internalization as a specific target for toxic effects of air pollution particles on AMs.

Key Words: concentrated ambient particles • macrophages • Streptococcus pneumoniae • phagocytosis • killing

CLINICAL RELEVANCE The data identify details of how air pollution particles reduce lung macrophage antibacterial function. This may lead to therapies to protect people from the increased risk of pneumonia that is linked to particulate air pollution.