Afferent selective vagus nerve stimulation reduces TLR7 induced acute lung inflammation
Authors: Murray Kaitlin , Cremin Michael , Schreiber Sierra , Baumgarth Nicole , Reardon Colin 
Published: May 2023

Background: Vagus nerve stimulation (VNS) has recently been introduced as a nonpharmacological therapy for disease characterized by an exacerbated immune response, with clinical trials demonstrating its efficacy for autoimmunity and sepsis by reducing inflammatory proteins and improving disease scores. To date, much of these anti-inflammatory effects have been attributed to vagal efferent (motor) signaling in a mechanism referred to as the cholinergic anti-inflammatory pathway (CAIP). Recent studies from our lab, as well as others, have begun to highlight alternative neuro-immune regulation by the vagus nerve, independent from the CAIP. The scope of these neuro-immune interactions, including target tissues and cell types, however, is still unclear. Although the lung is densely innervated, it is unknown how VNS can reduce acute TLR7 agonist-induced lung inflammation. Hypothesis: We sought to determine whether VNS was effective at reducing acute lung inflammation induced by viral mimetic and TLR7/8 agonist Resiquimod (R848). Methods: The right cervical vagus nerves of C57BL/6 mice were stimulated electrically (5V, 5Hz) for 20 minutes. A 0.25mg/kg dose of R848 was instilled 10 minutes after beginning VNS. 1 hour post-R848 challenge, relevant tissues were prepared for qPCR, flow cytometry, or ELISA. Results: Stimulation of the right vagus nerve was able to significantly decrease R848-induced mRNA expression of pro-inflammatory cytokines TNFα and IFNβ, as well as chemokines CCL4 and CXCL1 within the lung. This decrease occurred independently of the cells responsible for the CAIP (CD4+ ChAT+ T-cells), indicating a novel neuro-immune mechanism with a new target organ. Flow cytometry revealed that alveolar macrophages and neutrophils were the primary immune cell populations responding to R848 and subsequently modified by VNS, with significant reductions in intracellular staining for TNFα. Epinephrine and norepinephrine were significantly elevated within the serum during the first 5 minutes of VNS, but fluid from bronchoalveolar lavage revealed significant increases of only epinephrine within the lung. Subsequently, removal of the adrenal glands, the primary source of epinephrine, eliminated the anti-inflammatory effect of VNS. Elevation of epinephrine suggests an immunomodulatory role for the β2AR, with further studies using a highly selective antagonist ICI 118 551 or β2AR KO mice eliminating VNS-induced protection. Finally, using optogenetics we were able to identify vagal afferent neurons as the fibers responsible for modulating immune cell activation within the lung. Conclusion: These studies highlight a novel neuro-immune mechanism within the lung capable of regulating viral mimetic-induced inflammation. Facilitated by vagal afferent neurons, we show that VNS elicits adrenal gland-derived epinephrine release that acts through the β2AR to reduce macrophage activation and neutrophil recruitment in the lung. Chan-Zuckerberg Initiative (2020-217656); Graduate Student Support Program (UC Davis: School of Veterinary Medicine); NIH T32 GM (GM099608, GM144303) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.