Background: In models of sepsis and postoperative ileus, vagus nerve (VN) stimulation dampens inflammation via acetylcholine interacting with alpha7 nicotinic receptors (α7nAChR) on macrophages. This so-called cholinergic anti-inflammatory system is also involved in modulating colitis, as evidenced by increased severity of colitis in mice that underwent vagotomy (VGX). To what extent this effect is also mediated by α7nAChR remains however to be defined. Methods: The role of VN and α7nAChR in oral tolerance and experimental colitis was studied using respectively VGX and α7nAChR knock-out mice (Chrna7-/-). To induce oral tolerance, mice were fed with ovalbumin (OVA) and then systemically immunized against OVA. One week later, mice were challenged with OVA by footpad injection and 48hours later, swelling was measured to assess the induction of oral tolerance. Moreover, in vivo antigen specific T regulatory cells (Tregs) conversion of transfused OTII T cells was performed in wild type (WT) and Chrna7-/mice. Additionally, the role of VN and α7nAChR was investigated in DSS (dextran sulfate sodium) and T cell transfer colitis. Results: OVA oral feeding resulted in oral tolerance and absence of footpad swelling in WT and Chrna7-/mice. In contrast, VGX mice developed footpad swelling indicating loss of oral tolerance (Figure 1). In line, OVA specific naive T cells revealed a similar proliferation and conversion rate into Tregs in the small intestine lamina propria of both Chrna7-/and WT mice arguing against α7nAChR in mucosal immune homeostasis. During DSS colitis, VXG mice developed more severe disease as shown by increased body weight loss (Figure 2), higher pro-inflammatory cytokine gene expression and reduced Treg subset in the colon, while no difference was observed between WT and Chrna7-/mice. To further study the role of α7nAChR, adoptive transfer of naive T cells from WT mice into Chrna7-/-Rag1-/and Chrna7+/+Rag1-/recipient mice was performed. Three weeks after T cell transfer, WT→Chrna7-/-Rag1-/and WT→Chrna7+/+Rag1-/-mice showed similar body weight (respectively 90,4±1,5% vs 90,7±1,0 % of initial body weight, not significant) and comparable disease severity assessed by means of colon length, pro-inflammatory cytokine gene expression and T cell subsets in the colon. In accordance, adoptive transfer of naive Chrna7-/and WT T cells into Rag1-/recipients also showed equivalent severity of colitis confirming no role for α7nAChR. Conclusion: VGX impairs the ability to develop oral tolerance and results in increased severity of DSS colitis however these effects are not observed in Chrna7-/mice. Additionally, no role for α7nAChR could be proven (either on transferred T cells or in the recipient) in transfer colitis. These data indicate that the endogenous anti-cholinergic input to the intestinal immune system is independent of α7AChR.
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Sep 1, 2024
Shantala S Herlekar + 3
Open Access