Protection from Pulmonary Fibrosis in the Absence of CCR2 Signaling

Abstract

Pulmonary fibrosis can be modeled in animals by intratracheal instillation of FITC, which results in acute lung injury, inflammation, and extracellular matrix deposition. We have previously shown that despite chronic inflammation, this model of pulmonary fibrosis is lymphocyte independent. The CC chemokine monocyte-chemoattractant protein-1 is induced following FITC deposition. Therefore, we have investigated the contribution of the main monocyte-chemoattractant protein-1 chemokine receptor, CCR2, to the fibrotic disease process. We demonstrate that CCR2−/− mice are protected from fibrosis in both the FITC and bleomycin pulmonary fibrosis models. The protection is specific for the absence of CCR2, as CCR5−/− mice are not protected. The protection is not explained by differences in acute lung injury, or the magnitude or composition of inflammatory cells. FITC-treated CCR2−/− mice display differential patterns of cellular activation as evidenced by the altered production of cytokines and growth factors following FITC inoculation compared with wild-type controls. CCR2−/− mice have increased levels of GM-CSF and reduced levels of TNF-α compared with FITC-treated CCR2+/+ mice. Thus, CCR2 signaling promotes a profibrotic cytokine cascade following FITC administration.

Negative Regulation of Lung Inflammation and Immunopathology by TNF-α during Acute Influenza Infection

“…MCP-1 has previously been reported to be a major profibrotic chemokine involved in various fibrotic processes, including recruitment of fibrocytes, induction of collagen synthesis, and up-regulation of TGF-␤1 expression in various models. 50,51,[55][56][57][58][59][60][61][63][64][65][66][67][68] Indeed, we observed that MCP-1 responses preceded the responses of fibrogenic growth factor TGF-␤1, 51,52 which were significantly higher in the lung of infected TNF Ϫ/Ϫ lungs and were well correlated with fibrotic tissue remodeling seen in TNF Ϫ/Ϫ lungs at later time points during influenza infection. Thus, depletion of MCP-1 in influenza-infected TNF Ϫ/Ϫ hosts markedly reduced lung immunopathology and tissue remodeling, and such MCP-1 depletion-improved welfare was associated with diminished production of bioactive TGF-␤1.…”

“…51,[62][63][64][65][66][67][68] Thus, given the dysregulated MCP-1 and its association with heightened TGF-␤1 production seen in influenza-infected TNF Ϫ/Ϫ lungs (Figure 7), we further investigated the role of MCP-1 in heightened immunopathology and fibrotic reaction in the lung of TNF Ϫ/Ϫ mice by means of MCP-1 depletion. To this end, MCP-1 anti-serum (anti-MCP-1) or the control serum was administered intraperitoneally to TNF Ϫ/Ϫ mice on days 2, 5, and 9 following influenza infection, and the mice were sacrificed at day 21 after infection for morphometric quantification of lung immunopathology and fibrotic remodeling ( Figure 8A).…”

CCR2-Mediated Recruitment of Fibrocytes to the Alveolar Space after Fibrotic Injury

“…8 Briefly, mice were anesthetized with sodium pentobarbital. The trachea was exposed and entered with a needle under direct visualization.…”

“…9, 10 We previously demonstrated that mice that are deficient in CCR2 (CCR2 Ϫ/Ϫ mice) are protected from the development of experimental pulmonary fibrosis induced either by FITC or bleomycin. 8 However, recruitment of classical inflammatory cells (monocytes, macrophages, eosinophils, neutrophils, T, B, or NK cells) to the lung in response to FITC was not diminished when CCR2 Ϫ/Ϫ mice were compared to CCR2 ϩ/ϩ mice. 8 Because altered recruitment of classical inflammatory cells was not noted, we determined whether CCR2 played a role in mesenchymal cell recruitment to the lung in response to injury.…”

“…[1][2][3][4][5][6] In animals, the disease process can be modeled via the intratracheal administration of fluorescein isothiocyanate (FITC). 7,8 Soluble monocyte chemoattractant protein-1 (CCL2) levels in the bronchoalveolar lavage (BAL) fluid peak by day 1 after FITC and remain elevated until day 7; 8 matrix-bound CCL2 is bioactive and evident through day 21 after FITC. CC chemokine receptor 2 (CCR2) is the high-affinity receptor for CCL2.…”