Adenosine receptor A2b on hematopoietic cells mediates LPS-induced migration of PMNs into the lung interstitium.

Uncontrolled transmigration of polymorphonuclear leukocytes (PMNs) into the different compartments of the lungs (intravascular, interstitial, alveolar) is a critical event in the early stage of acute lung injury and acute respiratory distress syndrome. Adenosine receptor A(2b) is highly expressed in the inflamed lungs and has been suggested to mediate cell trafficking. In a murine model of LPS-induced lung inflammation, we investigated the role of A(2b) on migration of PMNs into the different compartments of the lung. In A(2b)(-/-) mice, LPS-induced accumulation of PMNs was significantly higher in the interstitium, but not in the alveolar space. In addition, pulmonary clearance of PMNs was delayed in A(2b)(-/-) mice. Using chimeric mice, we identified A(2b) on hematopoietic cells as crucial for PMN migration. A(2b) did not affect the release of relevant chemokines into the alveolar space. LPS-induced microvascular permeability was under the control of A(2b) on both hematopoietic and nonhematopoietic cells. Activation of A(2b) on endothelial cells also reduced formation of LPS-induced stress fibers, highlighting its role for endothelial integrity. A specific A(2b) agonist (BAY 60-6583) was effective in decreasing PMN migration into the lung interstitium and microvascular permeability. In addition, in vitro transmigration of human PMNs through a layer of human endothelial or epithelial cells was A(2b) dependent. Activation of A(2b) on human PMNs reduced oxidative burst activity. Together, our results demonstrate anti-inflammatory effects of A(2b) on two major characteristics of acute lung injury, with a distinct role of hematopoietic A(2b) for cell trafficking and endothelial A(2b) for microvascular permeability.