Modulation of Cytokine Secretion from Thp‐1 Macrophages by Adenosine Receptors

Abstract

Macrophages serve a major role in the innate immune system by directing the inflammatory response in tissues. By secreting cytokines and chemokines, macrophages direct other immune cells to sites of inflammation. Once inflammatory stimuli are removed, macrophages play a major role in initiating resolution of inflammation by secreting anti‐inflammatory cytokines, greatly influencing immune function and chemotaxis. However, the signals which tune cytokine production towards resolution of inflammation are not yet fully understood. Small metabolites such as adenosine can initiate cell signaling pathways which direct cytokine secretion. Adenosine acts on four cell surface g‐protein coupled receptors (A1, A2A, A2B, and A3 adenosine receptors) and is understood to be a potent immunosuppressive molecule by stimulating IL‐10 secretion. However, the full influence of adenosine receptor agonism on cytokine secretion is not known. Therefore, our primary aim was to determine how adenosine alters the pattern of cytokines secreted during an inflammatory response. We used a multiplex immunoassay to measure secretion of several cytokines in conditioned medium from LPS‐stimulated THP‐1 monocyte derived macrophages treated with adenosine or a vehicle control. We also used siRNAs directed against each adenosine receptor to determine which receptor mediated the effect of adenosine on each of these cytokines. LPS‐stimulated THP‐1 macrophages treated for four hours with adenosine showed increased IL‐10 and IL‐1β secretion and reduced IL‐6 and MCP‐1 secretion. We found the A1 receptor is required for the stimulatory effect of adenosine on IL‐10 and IL‐1β secretion while the A2B receptor is required for the inhibitory effect of adenosine on IL‐6 and MCP‐1 secretion. We also show that under basal adenosine concentrations the adenosine receptors serve to suppress and modulate various cytokines. These data show adenosine receptors are important regulators of cytokine secretion in macrophages. Adenosine, by signaling through the A1 and A2B adenosine receptors, stimulates IL‐10 and IL‐1β secretion while reducing IL‐6 and MCP‐1 secretion which signals priming of immune cells and tips the balance towards a pro‐resolution state which is of value in the context of several pathologies involving chronic inflammation such as metabolic syndrome, arthritis, and cancer. Future studies should determine how adenosine, by altering cytokine patterns, may affect other aspects of macrophage phenotype including ROS production and phagocytic function.Support or Funding InformationFunded by the UF/IFAS Agricultural Experiment Station.