Cholinergic receptors modulate immune complex-induced inflammation in vitro and in vivo

Cholinergic neural output has been shown to modulate innate immune responses to infection, injury and ischemia through stimulation of α7 nicotinic acetylcholine receptors (α7nAChR) on mononuclear phagocytes. We tested the hypothesis that cholinergic neurotransmitters, similar to those released through activation of a neural reflex, regulate responses to products of the adaptive immune system, specifically immune complex (IC)-mediated activation of effector cells. In this study, we show that stimulation of α7nAChR on human polymorphonuclear neutrophils (PMNs) and blood mononuclear phagocytes in vitro attenuates C5aR- and FcγR-triggered generation of reactive oxygen species, expression of leukocyte markers involved in cell recruitment and adhesion, and release of TNF-α and other proinflammatory cytokines. We show that this pathway is operative in vivo. Ligation of cholinergic receptors blunts IC-triggered responses in the reverse peritoneal Arthus reaction in mice. The selective 7nAChR agonist GTS21 decreased PMN accumulation and release of cytokines and chemokines at sites of IC deposition. In addition, mice lacking α7nAChR had exaggerated responses to reverse peritoneal Arthus reaction characterized by increased infiltration of PMNs and elevated of levels of TNF-α and CXCL1 in peritoneal fluid compared with wild-type mice. Taken together, these findings suggest that cholinergic output has the potential to exert tonic inhibitory activity that dampens responses to ICs and C5a and thus may be a target to minimize tissue damage in autoimmune diseases.