Adenosine receptor A 3 is a critical mediator in LPS-induced pulmonary inflammation

Adenosine receptor A 3 (A 3 ) regulates directed movement of polymorphonuclear cells (PMNs) to sites of inflammation and has been implicated as a relevant mediator in models of inflammatory diseases. Here, we sought to characterize the role of A 3 in a murine model of lung inflammation. Initial studies revealed that pulmonary A 3 transcript levels were elevated following LPS exposure in vivo. In addition, inhalation of LPS increased the accumulation of PMNs in wild-type and A 3 −/− mice in all lung compartments. Pretreatment with the specific A 3 -agonist Cl-IB-MECA significantly decreased migration of PMNs into lung interstitium and alveolar air space of wild-type mice but not of A 3 −/− mice. Lower PMN counts were associated with reduced levels of TNF-α and IL-6 in the alveolar space of wild-type mice that received Cl-IB-MECA. In addition, Cl-IB-MECA attenuated LPS-induced microvascular permeability in wild-type mice as assessed by the extravasation of Evans blue. In pulmonary microvascular endothelial cells, Cl-IB-MECA reduced LPS-induced cytoskeletal remodeling and cell retraction, consistent with a specific role of A 3 for maintaining endothelial integrity. Migratory activity of human PMNs across an endothelial or epithelial monolayer was reduced when A 3 was activated on PMNs. Studies in chimeric mice, however, revealed that Cl-IB-MECA required A 3 on both hematopoietic and nonhematopoietic cells to reduce transmigration in vivo. Together, our results shed new light on the role of A 3 in LPS-induced PMN trafficking in the lung and suggest pharmacological modulation of A 3 -dependent pathways as a promising approach in lung inflammation.