The formation of adenosine dampens inflammation by inhibiting most cells of the immune system. Among its actions on neutrophils, adenosine suppresses superoxide generation and regulates chemotactic activity. To date, most evidence implicates the Gs protein-coupled A2A adenosine receptor (AR) as the primary AR subtype responsible for mediating the actions of adenosine on neutrophils, by stimulating cAMP production. Given that the A2BAR is now known to be expressed in neutrophils and that it is a Gs protein-coupled receptor, we examined in this study whether it signals to suppress neutrophil activities using BAY 60-6583, a new agonist for the human A2BAR that was confirmed in preliminary studies to be a potent and highly selective agonist for the murine A2BAR. We found that treating mouse neutrophils with low concentrations (10-9 & 10-8 M) of BAY 60-6583 inhibited fMLP-stimulated superoxide production by either naive neutrophils, TNF-α-primed neutrophils, or neutrophils isolated from mice treated systemically with lipopolysaccharide. This inhibitory action of BAY 60-6583 was confirmed to involve the A2BAR in experiments using neutrophils obtained from A2BAR gene knock-out mice. Interestingly, BAY 60-6583 increased fMLP-stimulated superoxide production at higher concentrations (>1 μM), which was attributed to an AR-independent effect. In a standard Boyden chamber migration assay, BAY 60-6583 alone did not stimulate neutrophil chemotaxis or influence chemotaxis in response to fMLP. These results indicate that the A2BAR signals to suppress oxidase activity by murine neutrophils, supporting the idea that this low-affinity receptor for adenosine participates along with the A2AAR in regulating the pro-inflammatory actions of neutrophils.
- Received March 17, 2011.
- Revision received June 16, 2011.
- Accepted June 16, 2011.
- The American Society for Pharmacology and Experimental Therapeutics