Regulatory T cells reduce acute lung injury fibroproliferation by decreasing fibrocyte recruitment

Acute lung injury (ALI) causes significant morbidity and mortality. Fibroproliferation in ALI results in worse outcomes, but the mechanisms governing fibroproliferation remain poorly understood. Regulatory T cells (Tregs) are important in lung injury resolution. Their role in fibroproliferation is unknown. We sought to identify the role of Tregs in ALI fibroproliferation, using a murine model of lung injury. Wild-type (WT) and lymphocyte-deficient Rag-1-/- mice received intratracheal LPS. Fibroproliferationwascharacterizedby histology and the measurement of lung collagen. Lung fibrocytes were measured by flow cytometry. To dissect the role of Tregs in fibroproliferation, Rag-1-/- mice received CD4 +CD25+ (Tregs) or CD4+ CD25- Tcells (non-Tregs) at the time of LPS injury. To define the role of the chemokine (C-X-C motif) ligand 12 (CXCL12)-CXCR4 pathway in ALI fibroproliferation, Rag-1-/- mice were treated with the CXCR4 antagonist AMD3100 to block fibrocyte recruitment. WT and Rag-1-/- mice demonstrated significant collagen deposition on Day 3 after LPS. WT mice exhibited the clearance of collagen, but Rag-1-/- mice developed persistent fibrosis. This fibrosis was mediated by the sustained epithelial expression of CXCL12 (or stromal cell-derived factor 1 [SDF-1]) that led to increased fibrocyte recruitment. The adoptive transfer of Tregs resolved fibroproliferation by decreasing CXCL12 expression and subsequent fibrocyte recruitment. Blockade of the CXCL12-CXCR4 axis with AMD3100 also decreased lung fibrocytes and fibroproliferation. These results indicate a central role for Tregs in the resolution of ALI fibroproliferation by reducing fibrocyte recruitment along the CXCL12-CXCR4 axis. A dissection of the role of Tregs in ALI fibroproliferation may inform the design of new therapeutic tools for patients with ALI

Macrophage A2A adenosinergic receptor modulates oxygen-induced augmentation of murine lung injury

Acute respiratory distress syndrome (ARDS) causes significant morbidity and mortality. Exacerbating factors increasing the risk of ARDS remain unknown. Supplemental oxygen is oftennecessary inbothmild and severe lung disease. The potential effects of supplemental oxygen may include augmentation of lung inflammation by inhibiting antiinflammatory pathways in alveolar macrophages. We sought to determine oxygen- derived effects on the anti-inflammatory A2A adenosinergic (ADORA2A) receptor in macrophages, and the role of the ADORA2A receptor in lung injury. Wild-type (WT) and ADORA2A-/- mice received intratracheal lipopolysaccharide (IT LPS), followed 12 hours later by continuous exposure to 21% oxygen (control mice) or 60% oxygenfor1to3days. Wemeasuredthephenotypic endpoints of lung injury and the alveolarmacrophage inflammatory state.We tested an ADORA2A-specific agonist, CGS-21680 hydrochloride, in LPS plus oxygen-exposed WT and ADORA2A-/- mice. We determined the specific effects of myeloid ADORA2A, using chimera experiments. Compared with WT mice, ADORA2A-/- mice exposed to IT LPS and 60%oxygen demonstrated significantly more histologic lung injury, alveolar neutrophils, and protein. Macrophages from ADORA2A-/- mice exposedto LPS plus oxygen expressed higher concentrations of proinflammatory cytokines and cosignaling molecules. CGS- 21680 prevented the oxygen-induced augmentation of lung injury after LPS only in WT mice. Chimera experiments demonstrated that the transfer of WT but not ADORA2A-/- bone marrow cells into irradiated ADORA2A-/- mice reduced lung injury after LPS plus oxygen, demonstrating myeloid ADORA2A protection. ADORA2A is protective against lung injury after LPS and oxygen. Oxygen after LPS increases macrophage activation to augment lung injury by inhibiting the ADORA2A pathway