Inhibition of acute lung inflammation by a neuroimmune circuit induced by vagal nerve stimulation

Vagus nerve stimulation (VNS) has been shown to limit immune cell activity across several pathologies ranging from sepsis to auto-immune diseases. While stimulation of vagal efferent neurons has been previously demonstrated to reduce maladaptive host responses during endotoxemia, only selective stimulation of vagal afferent neurons was able to inhibit TLR7-induced macrophage activation and neutrophil recruitment in the lung. These anti-inflammatory actions are facilitated by systemic increases in epinephrine, as VNS significantly increased epinephrine in the serum and bronchoalveolar lavage fluid, and inhibition of epinephrine production eliminated the protection afforded by VNS. Selective afferent VNS induced activation in the nucleus tractus solitarius and the rostral ventrolateral medulla. Inhibition of neuronal activity in this brain region that controls peripheral sympathetic nervous system activity rendered VNS ineffective. Activation of the β₂-adrenergic receptor (β₂AR) is critical for innate immune cell suppression, as the anti-inflammatory effects of VNS were eliminated in β₂AR-knock out mice, and with pharmacological inhibition of the β₂AR. Analysis of the immune cells responding to R848 critically identified that plasmacytoid dendritic cells were refractive to inhibition by VNS, and this corresponded to lack of β₂AR expression. These findings demonstrate a novel neuro-immune circuit elicited by VNS that can control acute lung inflammation.