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Ly6Chi monocytes direct alternatively activated profibrotic macrophage regulation of lung fibrosis.

TitleLy6Chi monocytes direct alternatively activated profibrotic macrophage regulation of lung fibrosis.
Publication TypeJournal Article
Year of Publication2011
AuthorsGibbons MA, Mackinnon AC, Ramachandran P, Dhaliwal K, Duffin R, Phythian-Adams AT, van Rooijen N, Haslett C, Howie SE, A Simpson J, Hirani N, Gauldie J, Iredale JP, Sethi T, Forbes SJ
JournalAm J Respir Crit Care Med
Date Published2011 Sep 1
KeywordsAnimals, Bleomycin, Disease Models, Animal, Disease Progression, Female, Humans, Immunity, Cellular, Macrophage Activation, Macrophages, Alveolar, Mice, Monocytes, Phenotype, Pulmonary Fibrosis

RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a devastating disease. Antiinflammatory therapies, including corticosteroids, are of no benefit. The role of monocytes and macrophages is therefore controversial.

OBJECTIVES: To define the role of monocytes and macrophages during lung fibrogenesis and resolution, and explore the phenotype of the cells involved.

METHODS: We used multiple in vivo depletional strategies, backed up by adoptive transfer techniques. Further studies were performed on samples from patients with IPF.

MEASUREMENTS AND MAIN RESULTS: Depletion of lung macrophages during fibrogenesis reduced pulmonary fibrosis as measured by lung collagen (P = 0.0079); fibrosis score (P = 0.0051); and quantitative polymerase chain reaction for surrogate markers of fibrosis Col1 (P = 0.0083) and a-smooth muscle actin (P = 0.0349). There was an associated reduction in markers of the profibrotic alternative macrophage activation phenotype, Ym1 (P = 0.0179), and Arginase 1. The alternative macrophage marker CD163 was expressed on lung macrophages from patients with IPF. Depletion of Ly6Chi circulating monocytes reduced pulmonary fibrosis (P = 0.0052) and the number of Ym1- positive alternatively activated lung macrophages (P = 0.0310). Their adoptive transfer during fibrogenesis exacerbated fibrosis (P = 0.0304); however, adoptively transferred CD45.1 Ly6Chi cells were not found in the lungs of recipient CD45.2 mice.

CONCLUSIONS: We demonstrate the importance of circulating monocytes and lung macrophages during pulmonary fibrosis, and emphasize the importance of the alternatively activated macrophage phenotype. We show that Ly6Chi monocytes facilitate the progression of pulmonary fibrosis, but are not obviously engrafted into lungs thereafter. Finally, we provide empirical data to suggest that macrophages may have a resolution-promoting role during the reversible phase of bleomycin-induced pulmonary fibrosis.

Alternate JournalAm. J. Respir. Crit. Care Med.
PubMed ID21680953
Grant ListG0600033 / / Medical Research Council / United Kingdom
G0601401 / / Medical Research Council / United Kingdom
G0601409 / / Medical Research Council / United Kingdom
G1000868 / / Medical Research Council / United Kingdom
/ / Medical Research Council / United Kingdom