G2A Protects Mice against Sepsis by Modulating Kupffer Cell Activation: Cooperativity with Adenosine Receptor 2b.

G2A is a GPCR abundantly expressed in immune cells. G2A mice showed higher lethality, higher plasma cytokines, and an impaired bacterial clearance in response to a murine model of sepsis (cecal ligation and puncture), which were blocked by GdCl, an inhibitor of Kupffer cells. Anti-IL-10 Ab reversed the impaired bacterial clearance in G2A mice. Indomethacin effectively blocked both the increased i.p. IL-10 levels and the impaired bacterial clearance, indicating that disturbed PG system is the proximal cause of these phenomena. Stimulation with LPS/C5a induced an increase in phagocytosis and intracellular cAMP levels in G2A peritoneal macrophages but not G2A cells, which showed more PGE/nitrite release and intracellular reactive oxygen species levels. Heterologous coexpression of G2A and adenosine receptor type 2b (A2bAR) induced a synergistic increase in cAMP signaling in a ligand-independent manner, with the evidence of physical interaction of G2A with A2bAR. BAY 60-6583, a specific agonist for A2bAR, increased intracellular cAMP levels in Kupffer cells from G2A but not from G2A mice. Both G2A and A2bAR were required for antiseptic action of lysophosphatidylcholine. These results show inappropriate activation of G2A Kupffer cells to septic insults due to an impaired cAMP signaling possibly by lack of interaction with A2bAR.