Auto/paracrine control of inflammatory cytokines by acetylcholine in macrophage-like U937 cells through nicotinic receptors

Although acetylcholine (ACh) is well known for its neurotransmitter function, recent studies have indicated that it also functions as an immune cytokine that prevents macrophage activation through a ‘cholinergic (nicotinic) anti-inflammatory pathway’. In this study, we used the macrophage-like U937 cells to elucidate the mechanisms of the physiologic control of cytokine production by auto/paracrine ACh through the nicotinic class of ACh receptors (nAChRs) expressed in these cells. Stimulation of cells with lipopolysaccharide up-regulated expression of α1, α4, α5, α7, α10, β1 and β3 subunits, down-regulated α6 and β2 subunits, and did not alter the relative quantity of α9 and β4 mRNAs. Distinct nAChR subtypes showed differential regulation of the production of pro- and anti-inflammatory cytokines. While inhibition of the expression of the TNF-α gene was mediated predominantly by the α-bungarotoxin sensitive nAChRs, that of the IL-6 and IL-18 genes—by the mecamylamine-sensitive nAChRs. Both the Mec- and αBtx-sensitive nAChRs regulated expression of the IL-1β gene equally efficiently. Upregulation of IL-10 production by auto/paracrine ACh was mediated predominantly through α7 nAChR. These findings offer a new insight on how nicotinic agonists control inflammation, thus laying a groundwork for the development of novel immunomodulatory therapies based on the nAChR subtype selectivity of nicotinic agonists.