Pro-inflammatory responses in human monocytes are β1-adrenergic receptor subtype dependent

Stress induced circulating catecholamines are hypothesized to selectively activate adrenergic receptors (ARs) on immunocompetent cells modulating their inflammatory response to trauma or environmental toxins. We characterized changes in expression of a pro-inflammatory cytokine modulated by β-AR activation in human primary and immortalized monocytes that had been simultaneously stimulated with lipopolysaccharide (LPS). Results from cytokine antibody arrays demonstrated that half-maximal effective concentrations of the selective β-AR agonist isoproterenol (Iso) qualitatively increased LPS-mediated expression of the soluble cytokine, interleukin-1β (IL-1β). Semi-quantitative immunoblot techniques confirmed a synergistic increase of IL-1β production in both LPS stimulated THP-1 cells and primary human monocytes co-incubated with Iso. Immunoblot techniques as well as radioligand binding studies were also used to characterize the heterogeneous expression of β1- and β2-AR subtypes on THP-1 cells. β-AR activation is classically associated with generation of cAMP in many tissues and cell types. Therefore, using the method of Schild, we generated Iso concentration-response curves in the presence of fixed subtype-selective β-AR antagonist concentrations to demonstrate that β1-AR activation was exclusively linked with the generation of cAMP in THP-1 cells. Furthermore, use of a selective kinase inhibitor demonstrated that Iso potentiated the expression of soluble IL-1β through activation of cAMP-dependent protein kinase A. Finally, discriminating concentrations of subtype-selective β-AR antagonists revealed that β1-AR stimulation alone accounted for the synergistic production of IL-1β in LPS stimulated monocytes co-incubated with Iso. These results demonstrate a unique synergistic pro-inflammatory response mediated through a β1-AR cAMP-dependent mechanism in LPS-challenged monocytic cells.