CD11c⁺/CD11b⁺ Cells Are Critical for Organic Dust–Elicited Murine Lung Inflammation

Abstract

Organic dust exposure in the agricultural industry results in significant lung disease. Macrophage infiltrates are increased in the lungs after organic dust exposures, yet the phenotype and functional importance of these cells remain unclear. Using an established intranasal inhalation murine model of dust-induced lung inflammation, animals were treated once or daily for 3 weeks with swine confinement organic dust extract (DE). Repetitive DE treatment for 3 weeks resulted in significant increases in CD11c(+)/CD11b(+) macrophages in whole lung-associated tissue. These cells displayed increased costimulatory molecule (CD80 and CD86) expression, enhanced phagocytic ability, and an increased production of IL-6, CXCL1, and CXCL2. Similar findings were observed with the CD11c(+)/CD11b(+) macrophage infiltrate after repetitive exposure to peptidoglycan, a major DE component. To determine the functional importance of macrophages in mediating DE-induced airway inflammation, lung macrophages were selectively depleted using a well-established intranasal clodronate liposome depletion/suicide strategy. First, macrophage depletion by clodronate liposomes resulted in significant reductions in airway neutrophil influx and TNF-α and IL-6 production after a single exposure to DE. In contrast, after repetitive 3-week exposure to DE, airway lavage fluid and lung tissue neutrophils were significantly increased in clodronate liposome-treated mice compared with control mice. A histological examination of lung tissue demonstrated striking increases in alveolar and bronchiolar inflammation, as well as in the size and distribution of cellular aggregates in clodronate-liposome versus saline-liposome groups repetitively exposed to DE. These studies demonstrate that DE elicits activated CD11c(+)/CD11b(+) macrophages in the lung, which play a critical role in regulating the outcome of DE-induced airway inflammation.

Neutrophilic oxidative stress mediates organic dust-induced pulmonary inflammation and airway hyperresponsiveness

“…Animals exposed to OD display severe neutrophilia (34), and when the kinetics have been studied, previous studies have shown that repeated OD exposure in mice results in a marked increase in pulmonary neutrophil populations that peak 24 h following OD exposure (33). Due to the efficacy of 100 g of OD in inducing AHR as well as increased macrophage and neutrophil numbers in BAL in the present study, this dose was well-suited for all subsequent experiments, as both macrophages and neutrophils have been shown to be important in mediating the OD response (32).…”

“…Similarly, OD exposure induces pulmonary inflammation in humans typified by an increase in neutrophils and macrophages in BAL fluid (19,29,32). Animals exposed to OD display severe neutrophilia (34), and when the kinetics have been studied, previous studies have shown that repeated OD exposure in mice results in a marked increase in pulmonary neutrophil populations that peak 24 h following OD exposure (33).…”

Organic Dust, Lipopolysaccharide, and Peptidoglycan Inhalant Exposures Result in Bone Loss/Disease

“…Aqueous ODE was collected and prepared as previously described (14), and as described in the online supplement. To broaden the applicability of systemic ODE-induced lung injury bone consequences, comparison experiments were performed with LPS (100 ng per 30 ml, which is approximately double the concentration of detectable LPS in 12.5% ODE, from Escherichia coli O55:B5; Sigma Chemical Co., St. Louis, MO) and Staphylococcus aureus PGN (100 mg per 30 ml; Sigma Chemical Co.), which also remains consistent with our previous work comparing ODE-induced responses to PGN (6).…”

“…The organic dust exposure is complex, involving a wide diversity of microbial motifs (e.g., peptidoglycans [PGNs] and endotoxin) and particulate matter, which elicit airway inflammatory responses in mice (7,13). Namely, repetitive organic dust exposures induce the development of lymphoid aggregates and peribronchiolar/ vascular inflammation, comprised of T and B lymphocytes and macrophages with associated neutrophil recruitment (5,14,15). Although LPS remains an important component, the inflammatory lung response is not entirely dependent on LPS (6,16), and moreover, Gram-positive components, including PGN (7,13,17), appear to be the major factors driving lung consequences.…”

Flow Cytometric Analysis of Macrophages and Dendritic Cell Subsets in the Mouse Lung

“…In recent studies, several groups of investigators suggested that these two populations of lung macrophages play opposing roles in lung injury. Alveolar macrophages appear to limit neutrophil influx into the lung during acute lung injury (9) or chronic exposure to organic dust (10), whereas interstitial macrophages promote neutrophil extravasation (11,12). An additional layer of complexity is added by the phenotypic plasticity of macrophages.…”